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463 Cards in this Set

  • Front
  • Back
What are viruses?
Genetic intracellular parasites
What is the basic composition of a virus?
Nucleic acid - DNA or RNA
Protein shell
Envelope (some viruses)
What are the classes of virus by host?
1) Animal viruses
2) Bacteriophages
3) Plant viruses

This Classification is determined by selective binding
What are systems viruses completely dependent on the host cells for?
1) Protein synthesis
2) Some components for nucleic acid replication or transcription
3) Energy producing systems
Definition of Capsid?
Protein shell that encloses the nucleic acid
Definition of Nucleocapsid?
Capsid + nucleic acid
Definition of Capsomers?
Protein structural units of the capsid
Definition of Envelope?
Encloses the nucleocapsid in some viruses - membrane
Definition of Virion?
Complete infective virus particle
What are the major virus morphologies, and what are they common to?
1) Helical structure - open. Many plant viruses (TMV)
2) Cubic symmetry - Icosahedron, closed structure, stable. Regular polyhedron with 20 triangular faces and 12 corners. ***Many animal viruses (papilloma, herpes, adenovirus)
3) Complex viruses - Multiple surface layers (lipid bilayer, lipid layer), surface tubules, many other structures. Huge particles.
Example of a double caspid shell?
Reoviruses
What unique structure do Reoviruses have?
Double capsid shell
Example of Icosahedron head and tail?
Phage T4
What unique structure do Phage T4 have?
Icosahedron and Tail
What are the types of DNA viruses?
Generally classified as double stranded (d.s.) or single stranded (s.s.)

linear d.s.
circular d.s.
supercoiled d.s.
linear s.s.
circular s.s.
Types of RNA viruses?
***Most animal RNA viruses have s.s. RNA

s.s. RNA can be Positive (+) sense or Negative (-) sense.

Positive sense - The virion RNA = mRNA

Negative sense = The virion RNA = mirror image of the mRNA

The RNA genome can be in one piece or ***segmented
How is the genome localized on the RNA of an animal RNA virus?
It can be localized in one piece, or ***segmented
How is compression of information accomplished on viral genomes?
Overlapping coding sequences
Splicing
Use of two strands
What are the two types of proteins virions can code for?
1) Structural - Protection of the genome, bind cellular receptors, antigenic properties

2) Enzymes and regulatory proteins - transcription control, replication

Sometimes enzymes are part of the virion structure brought in with the virion
Where are lipids in the virion? Why?
In the envelope. They:

~Confer sensitivity to agents that dissolve lipids (ethers)
~Mostly belong to the host cell membrane, and are pinched off during budding
Where are carbohydrates located in the virion?
Glycoproteins in the envelope - ***virus encoded
What are the classification factors of viruses?
1) DNA or RNA
2) Symmetry - Helix, icosahedron, complex
3) Envelope - yes or no
4) Number of capsomers
5) Antigenic relationship
6) Nucleic acid sequence homologies
What are the classification criteria of the herpes simplex virus?
DNA - d.s.
Icosahedron
Envelope - yes
162 capsomers
2 antigenic types
What are the classification criteria of the polio virus?
RNA - s.s.
Icosahedron
Envelope - no
32 capsomers
3 antigenic types
What are the methods of virus detection?
1) Identification of the virus particles by physical methods - electron microscopy
2) Identification of viral components by immunological methods
3) Measurement by biological methods: measurement of viral infective properties in host cells - experimental animals, embryonated eggs, cell culture
What are the types of cell cultures used in virus detection?
1) Primary cultures
2) Immortalized cell cultures
3) Transformed cell lines
What is in the culture medium used for virus detection?
-Approximates blood plasma
-Contains most amino acids since animal cells can't synthesis many AA
-Vitamins
Glucose, as an energy source
-Antibiotics to preclude microbial contamination
-Blood serum, contains growth factors
What is the difference between a permissive and non-permissive cell?
Permissive cells have the proper machinery required to replicate the virus.

Non-permissive cells don't have the proper machinery to replicate the virus.
What cells are used for isolation and propagation of Herpes simplex?
Several primary, immortalized, and transformed cells
What cells are used for isolation and propagation of cytomegalovirus?
Primary human fibroblast cells
What cells are used for isolation and propagation of Polio?
Primate kidney cell lines
What cells are used for isolation and propagation of Influenza?
Primary and immortalized primate kidney cells or chick embryo fibroblasts
What cells are used for isolation and propagation of Hepatitis B?
Cannot be grown in tissue culture (duck HBV: immortal duck cell lines)
What cells are used for isolation and propagation of human retroviruses?
Immmortalized B and T cells
How are viruses detected?
1) Cytopathic effect
2) Proliferation foci
3) No visible changes in the cells - other means
Detecting virus-infected cells by the cytopathic effect is based on?
a) Cell lysis
b) Inclusion body formation
c) Giant cell formation
d) Cytoplasmic vacuolization
What is a proliferation foci?
Important for detecting virus infected cells.

Present with oncogenic viruses. Results from loss of contact inhibition, and cells pile up.
If there are no visible changes in a cell upon infection with a virus, how can it be detected?
1) Appearance of virus-encoded proteins (detection by antisera)
2) Hemadsorption
3) Interference by non-cytopathogenic viruses withr eplication or CPE induced by a "challenge" virus
How is quantification of a virus done?
1) Infectivity based assays - 50% end point, plaque assay
2) Hemagglutination
3) Assays based on antigenic properties - serologicla detection of viral infections, identification of viral antigens using labeled antibodies (RIA, ELISA
4) Identification of nucleic acids
What is the 50% end point, and what is it used for?
It is a test used to quantify a sample of viruses.

the ID50 or infectious dose 50, is the reciprocal of the dilution of virus that produces the effect in 50% of the cells or animals inoculated.

i.e. if 10^-5 dilution produces 50% of the effect, then the ID50 is 10^5
What is a plaque assay?
The most common assay used to quantify viruses. It is performed in semi-solid medium to limit the spread of the virus. In it, a virion infects a single cell replicating and infecting other cells. The net result is a plaque of dead cells in the lawn where the virus has grown. The virus population in a plaque is therefore the offspring of one virion, and a pure genetic clone.

PFU - plaque forming unit. 1-1000 virions = 1 PFU
What is hemagglutination?
Some viruses can agglutinate RBC with hemagglutinin, an external viral component.

In this test, the viruses are plated in a microtitre well with a sample of RBC. If hemagglutination occurs, the appearance of the RBCs in the microtitre well will be that of a large red dot.

If the same viruses and RBCs are plated into a well with antibodies against the hemagglutinin, then the appearance of the RBCs in the microtitre well will be a much smaller dot.

***This is not a sensitive method. Better used for detection then for quantification.

Hemagglutination units = reciprocal of the last hemagglutinating dilution. Many virions = 1 HA unit
What are the methods of detection of viruses by labeled antibodies?
1) Immunofluorescence - antibodies labeled by a fluorescent marker. Under stimulation by certain light, the marker gives off light of a different wavelength, which is detected. This makes possible identification of viruses ***inside*** the cell.
2) Radioimmunoassay (RIA) - Antibodies labeled by radioactive isotope (I-125). Advanted are ~Rapid, ~Sensitive (can detect small amounts of (ng), ~Specific - can distinguish between viral subtypes
3) ELISA - Enzyme linked immunosorbent assay - antibodies are labeled with an enzyme that participiates in a colorimetric or light-emitting reaction. ~Rapid, ~Sensitive, ~Specific, ~Non-radioactive
How can viruses be identified/detected by nucleic acids?
1) Hybridization with a radioactive probe. DISADVANTAGE - limited amount of nucleic acid in biological samples

2) Amplification of nucleic acids via PCR. ADVANTAGE - Can get large amounts of nucleic acid from minute amounts present in the sample, in a short time. DISADVANTAGE - Beward of amplification of lab contaminants.
For RNA viruses: RT-PCR (Reverse transcriptase PCR). First reverse transcribe RNA to DNA, then do PCR.
What are the steps of the replication cycle for viruses?
1) Attachment (adsorption)
2) Penetration
3) Uncoating
4) Gene expression
5) Replication
6) Assembly and mutation
7) Release of progeny particles
What are the common features of the reproductive cycles of a virus?
Eclipse phase - Initial decrease in percent of the virion population (compared to final yield)
Maturation phase - Increase in population until peaks at final yield
Inactivation or loss of virus - Decrease in population following peak
Does infection of a susceptible cell automatically ensure viral multiplication?
No, infection can be:

Productive - in permissive cells
Abortive - In non-permissive cells, allowing only partial virus gene expression OR as a result of infection with defective viruses.
Restrictive - In transiently permissive cells - the virus may persist in the cell until it becomes permissive, OR only a few cells in the population will produce virus
What is important about non-productiveinfections?
They may lead to latency or oncogenic transformation
Infection of a susceptible cell may lead to?
Productive - in permissive cells
Abortive - In non-permissive cells, allowing only partial virus gene expression OR as a result of infection with defective viruses.
Restrictive - In transiently permissive cells - the virus may persist in the cell until it becomes permissive, OR only a few cells in the population will produce virus
How is attachment of a virion to a host cell mediated?
Animal cell surface proteins, glycoproteins, sugars and glycolipids, all normal cell constituents, can be selected as a receptor by a virion.

They are not designed by the cell as virus receptors, but rather virus parasitize them.

Some viruses have many receptors and a broad host range, such as influenza which binds to sialic acid

Some viruses have very specific receptors and a narrow host range, such as:
HIV to CD4 on T-cells
EBV to CD21 on B cells
Measles to CD46
Rabies to Ach receptor on neurons
Vaccinia - EGFR
What virus is specific for the Ach receptor on neurons?
Rabies
What virus is specific for the EGFR?
Vaccinia
What virus is specific for CD21 on B cells?
EBV
What virus is specific for CD46 (complement receptor)?
Measles
What are Picornaviruses?
Polio and rhinoviruses. Both use an immunoglobulin like receptor
What is the virus-receptor interaction in human rhinovirus?
Intracellular Adhesion Molecule I (ICAM-I), a cellular adhesion molecule whose normal function ist o bind cells to adjacent substrates. It is similar to an immunoglobulin molecule with constant and variable domains.

Polio receptor is also an immunoglobulin-like molecule
What is the canyon hypothesis?
The rhinovirus attachment molecule is buried in a canyon like area. It is inaccessible to a neutralizing antibody, but accessible to the viral receptor, because it is narrow enough to reach the bottom of the canyon.
What happens if during attachment of viruses to cells?
Most of the time leads to irreversible changes in the structure of the virion.

In some cases, if no penetration occurs the virus can detach and readsorb to another cell.
How do energy and temperature play a roll in virion attachment to cells?
Attachment is usually an energy and temperature independent process
What are the three general mechanisms of viral penetration?
1) Translocation of the entire virus across the membrane
2) Direct fusion of enveloped capsids (envelope joins normal cell membrane)
3) Endocytosis - capsids, enveloped capsids. Virion then escapes endosome.

***Penetration is an energy dependent process.
What is uncoating?
The term for events where the capsid is completely or partially removed and the virus genome is exposed - usually in the form of a nucleoprotein complex.

**One of the least studied and poorly understood aspects of virus replication

****Eclipse preiod - the infecting virion is disrupted, loss of measurable infectivity
What are a virions two major problems, in regards to replication?
1) How to make mRNA from a genome
2) How to replicate the genome
What is replication?
The process of making more copies of the input particle. Replication strategy of any virus depends on both the nature of its genome and on cellular constraints
What are three major replicative constraints on viruses imposed by the cell?
1) Transcription and post-transcriptional events happen only in the nucleus. Only DNA viruses that multiply in the nucleus can use the cellular transcriptases

2) Eukaryotic cell protein synthesis machinery translated monocistronic messages from mRNA. Therefore, viruses must either synthesize seperate mRNA for each protein they want produced, OR a single mRNA that encodes a polyprotein that is then cleaved into several smaller proteins

3) Expression of the viral genome competes with expression of the host genes. Viruses overcome this by either: achieving a competitive advantage, or abolishing the synthesis or translation of cellular mRNAs.
What are the three general functions of viral encoded proteins?
1) Ensure replication of viral genomes
2) Package the genomes
3) Alter the structure and/or function of the infected cell
How is the viral genome replicated?
In most instances (picornaviruses, herpes) viral proteins replicate the genome, but use some host enzymes in the process.

In some cases, viral proteins assist host enzymes that replicate the viral genome
How are viral genomes packaged into virions?
ALWAYS viral proteins package the genome into virions, and sometimes host proteins may associate with viral genomes.
Virus Class I?
double stranded DNA
Virus Class II?
single stranded (+) DNA
Virus Class III?
double stranded RNA
Virus Class IV?
single stranded (+) RNA
Virus Class V?
single stranded (-) RNA
Virus Class VI?
single stranded (+) RNA with DNA intermediate
Virus Class VII?
double stranded DNA with RNA intermediate
What are the virus classes?
Class I - double stranded DNA
Class II - single stranded (+) DNA
Class III - double stranded RNA
Class IV - Single Stranded (+) RNA
Class V - Single Stranded (-) RNA
Class VI - single stranded (+) RNA with DNA intermediate
Class VII - double stranded DNA with RNA intermediate
What are examples of Class I viruses?
Class I - Double stranded DNA

Pox viruses (Vaccinia)
Adenoviruses
Herpes viruses
What are the characteristics of Vaccinia? How does it enter the host? How does it operate in the host and what are the effects?
Vaccinia is a large (230-300 nm) complex virus. d.s. DNA.

It binds to EGFR and is taken up in phagocytic vacuoles.

Complete life cycle is in the cytoplasm, where it established a "virus factory" = inclusion bodies

It is effectively independant of cellular mechanisms, needing only ribosomes, membranes, and small molecular weight precursors.

It packages many virus enzymes in the virion. Each virion has more then 100 different proteins.
What are the early genes of Vaccinia?
About 50% of the genome, they are expressed before replication inside a partially uncoated core particle. 5'-capped, 3'-polyA, but unspliced mRNA.
How does mRNA synthesis occur in Vaccinia?
By enzymes imported in the virion
What are the early proteins induced in Vaccinia infection?
***Proteins that stop cellular DNA and protein synthesis.

Transcriptional regulators.

Enzymes for DNA replication
How does replication of Vaccinia occur?
Replication is semi-conservative, by viral enzymes in the cytoplasm
What are the late genes in Vaccinia?
Expressed AFTER the genome replicates. Late proteins include mostly structural proteins and virion enzymes.
What events does maturation of Vaccinia entail?
Polypeptide modification, new membranes, virion assembly.
What are the characteristics of the Adenovirus?
Medium size, d.s. DNA virus.
Naked icosahedron.
Heavily dependent on cell machinery.

Encodes a strong multifunctional transcription regulator (E1A), and uses the cellular transcription machinery.
What are the functions of E1A, and how does it work?
Functions:
1) Transcriptional activator
2) Transcriptional repressor (some enhancers)
3) Cell-cycle regulator
4) Viral oncogene (together with E1B)

In an uninfected cell, Rb binds to E2F and blocks transcription. Normally, a kinase phosphorylates Rb at the G1/S border, releasing E2F to stimulate transcription.

E1A selectively binds Rb, freeing E2F to activate transcription.
How does Adenovirus shut-off the host cell?
1) Block of mRNA transport from nucleus to cytoplasm
2) Translational block
What are the characteristics of the Herpesviruses?
d.s. DNA viruses.
Enveloped Icosahedron
Less reliant on cellm achinery than adenoviruses and smaller DNA viruses

Encode many transcription regulators, but use cellular Pol II.

Encode many enzymes of DNA metabolism (TK, ribonucleotide reductase)

Encode own replication system: Herpes DNA polymerase as a target for anti-viral drugs.

Herpesvirus - Induces host cell shut-off

Maturation entails budding out of the nuclear membrane
For Herpesviruses, where does DNA replication occur?
In the nucleus
For Herpesviruses, where does virion assembly occur?
In the nucleus
What are the Herpesviruses subfamilies?
Alpha - Infect neurons
Beta - Infect monocytes, lymphocytes, and T-cells
Gamma - Infect B-cells
In Herpesvirus, what is the alpha/beta/gamma dynamic?
The virion initially promotes Alpha directly

Alpha then promotes both Beta and Gamma directly.

Beta promotes Gamma directly.

Gamma then blocks both Alpha and Beta directly.

Gamma also promotes the virion.
What type of virus is Picornavirus?
Polio, it is a Class IV - s.s. RNA (+) virus.
What type of virus is Rabies?
Class V - s.s. RNA (-)
What type of virus is Ebola?
Class V - s.s. RNA (-)
What type of virus are Reoviruses?
Class III - Double stranded RNA
What type of virus are Orthomyxoviruses
Influenza.

Segmented RNA
How does a Class IV virus replicate?
s.s. RNA (+)

It must use RNA dependent RNA polyemerase, to first create a RNA (-) template strand.

It then uses RNA dependent RNA polymerase to make RNA (+) strand progeny to be packaged into virions.

Because it can use host ribosomes to translate its genome directly, it only need encode RNA dep RNA pol, and not package it into the virion for replication to occur.
How does polycicstronic mRNA work in Class IV viruses?
Picornaviridae, Caliciviridae, Flaviviridae.

Polycicstronic mRNA makes polyprotein that is subsequently cleaved into smaller proteins.
What are the 4 common feature to all (+) strand RNA viruses?
1) Purified genomic RNA is infectious
2) Genomes look like mRNA
3) Replication enzymes are made ***after infection***, and not brought in with the virion
4) Encode for a huge polyprotein that is subsequently processed by viral proteases
How were Picornaviruses classically grouped?
By buoyant density and sensitivity to acid pH
What are 4 subtypes of Picornaviruses?
Enteroviruses: poliovirus
Rhinoviruses: common cold
Hepatoviruses: hepatitis A
Aphtoviruses: foot and mouth disease viruses
What are the characteristics of the Poliovirus?
27 nm.
Class IV - (+) RNA virus
Icosahedron
No envelope

Attachment by the canyon hypothesis

Synthesis of components all takes place in the cytoplasm.

Viral protein VPg is covalently linked to the 5' end of genomic RNA
What is IRES? Where is it located? What is it for?
IRES - Internal Ribosome Entry Site

Present in Poliovirus

It ensures cap-independent translation.

However, it still has to compete for common translation factors
What does the multifunctional enzyme encoded by Poliovirus do?
First it enhances specifically translation of mRNAs containing the polio 5' UTR.

Second, it functions as a viral protease to cleave the callular CAP-binding protein p220. Thus, cellular capped mRNAs cannot be translated
How does translation of the Poliovirus genome occur?
One large polypeptide is translated from the genomic mRNA, which is then cut into approximately 10 smaller proteins of distinct functions, such as VP1-VP4 (viral coat proteins), and RNA dep RNA pol.
How does Poliovirus cause host cell shut-off?
1) Cleavage of p220, the CAP-binding protein (thus blocking translation of host mRNA)

2) Inhibition of cellular transcription
How does RNA replication and virion release occur in Poliovirus?
A replicative intermediate, the (-) strand is copied from the (+) strand using RNA dep. RNA pol. This is accomplished using viral enzymes.

Maturation of the virion involves protein cleavage and assembly.

Progeny virions are released via cell destruction - the cell bursts releasing many virions
What types of Viruses carry RNA dep. RNA pol?
Class V - RNA (-) viruses
What must Class V viruses carry inside the virion to successfully replicate?
RNA dep. RNA pol.
What are the characteristics of Orthomyxovirus: Influenza?
Class V - RNA (-) virus
RNA is segmented - 8 segments
Helical structure
Enveloped
What are the major virion components of Orthomyxovirus: Influenza?
NA - Neuraminidase
HA - Hemagglutinin
Lipid Bilayer
M1 - Matrix Protein
M2 - Ion channel
How does the Influenza virus enter the host cell?
Adsorption - HA (Hemagglutinin) binds cell receptor

Penetration - by endocytosis and fusion
How and where does transcription and replication occur with the Influenza virus?
Both occur in the nucleus

1) Each segment is formed separately
2) mRNA is synthesized by virion enzymes: needs cellular CAP structures
3) RNA replication: by the same polymerases.
What is and is not co-terminal with genomic RNA in Influenza?
(+) RNA (antigenome)
mRNA is not
What determines the balance between transcription and translation in Influenza virus?
Nucleocapsid protein levels
How does maturation occur in the Influenza virus?
Two stages - nucleus and cell surface

Selection of a full complement of segments for each virion
What are antigenic drift and antigenic shift, and what do they most commonly affect in Influenza virus?
Antigenic drift is a gradual change in antigenicity due to point mutations that affect major antigenic sites. It results in a slow decrease in serological relatedness.

Antigenic shift is an abrupt change due to genetic re-assortment with an unrelated strain.

Most commonly affects Hemagglutinin (HA) and Neuraminidase (NA) in Influenza
What are the two types of genetic changes that occur in Influenza?
Antigenic Drift - slow
Antigenic Shift - sudden
What is the process of viral replication for Class VI viruses?
Retroviruses - Genome is a (+) sense RNA but uniquely diploid, and does NOT serve as mRNA

Genome is a template for reverse transcription

The integrated provirus DNA is a template for synthesis of genomic RNA (for the progeny) as well as mRNA for translation of viral proteins needed to completely form progeny.
What are examples of retroviruses?
Oncogenic viruses, HIV
What does the viral genome of retroviruses consist of?
RNA (+) strand attached to RNA dep DNA pol, also known as reverse transcriptase (RT)
How is the retroviral genome unique from other viruses?
1) The only diploid genome
2) The only one synthesized and processed by the cell's mRNA processing machinery
3) The only one associated with a specific RNA whose function is to prime replication
4) The only (+) strand RNA genome that does not serve as mRNA early in infection
How does reverse transcriptase work?
tRNA primer binds to the 5' primer binding site. RT binds to the tRNA and copies the 5' end of the RNA template.

At this point, the RNA that was copied to DNA is digested with RNase. The copy DNA now moves downstream to the 3' end of the RNA where it aligns, and RT again copies the remaining template.

RNase then digests the 5' and 3' ends of the RNA until the polypurine tract. RT then uses the DNA to make a DNA copy of what was the 3' end of the template RNA.

At this point, RNase digests the polypurine tract and tRNA.

there now exists a complementary sequence between the two strands, and they form a circular structure.

RT then uses the inner circle to finish copying the partial outer circle (was in the spot of the RNA template. Now the LTRs of the outer DNA are complete. The RT then jumps to the other DNA strand and completes the LTR of that strand.

The net result is a d.s. DNA with complete LTRs on both ends.
What is an LTR and where is it located?
Long Terminal Repeats

Present on the DNA provirus that is made in retroviruses
What is the basic schematic of Reverse Transcriptase action?
Virion (+) RNA ~~> s.s. DNA (-) ~~> d.s. DNA (+) ~~> Integration: provirus
How does transcription work for retroviruses?
The integrated viral DNA provirus is transcribed by the host RNA Pol II and other factors.

The products are:
1) mRNA (splicing)
2) Genomic RNA
What are the protein products Gag, Pol, and Env in retroviruses?
Gag - core proteins. Cleavage of a polyprotein

Pol - Polymerase and Integrase. Frameshift suppression: UUUAAAC

Env - Envelope proteins. mRNA obtained by splicing
What are the three fundamental strategies to assembly, maturation, and release of viruses?
1) Intracellular assembly and maturation: non-enveloped viruses such as picornaviruses and adenoviruses: in cytoplasm or nucleus. This class requires cell disintegration release

2) Enveloped viruses, including all (-) RNA viruses and retroviruses: viral proteins are inserted in the plasma membrane, nucleocapsids bud through. Cell disintegration is not required.

3) Herpesvirus: assembly in the nucleus, budding through the nuclear membrane. Cytolytic to the cell.
How does assembly work, and what are the processes for different viruses?
Critical concentration of components triggers assembly. Local high concentrations of components are visualized as "inclusion bodies"

~Helical structures assemble around strands of nucleic acid

~Icosahedral capsids are generally built as empty shells and stuffed with the genome

Complex viruses - subassembly lines to generate heads, tails, etc. before the final assembly
What is gD and what virus uses it?
gD is produced by HSV. It binds to the cell surface to new viruses cannot attach
How does neuraminidase work?
Present in influenza.

Neuraminidase strips off sialic acid on cell surfaces.

Required for virion release.
What are the properties of a transformed cell?
1) Change sin growth properties: high density, fast division rate, decreased requirement for growth factors, decreased adhesion to ECM, anchorage independance, loss of contact inhibition

2) Changes in cell membranes - Higher transport efficiency, protease secretion, antigenic changes

3) Changes in intracellular processes - higher metabolic rate, activation and repression of various genes, changes in the cytoskeleton, cells are more round

4) Tumorigenicity - cells injected into animals give rise to tumors. however, not every transformed cell in tissue culture can produce tumors in animals.
What are oncogenes?
Components of signal transduction pathways that control cell growth and differentiation
Where were oncogenes first discovered?
Retroviruses
Activation of oncogenes can lead to what 3 things?
1) Overexpression of a gene

2) Constitutive expression at the wrong time or in the wrong tissue

3) Mutations can change the interactions between a protein and other proteins or nucleic acids
What are the mechanisms of activation of oncogenes?
1) Transduction by Retroviruses
2) Insertional Mutagenesis
3) Translocation
4) Amplification
5) Mutations
How does activation of an oncogene by transduction with a retrovirus work?
Some retroviruses have an extra gene that is an oncogene, and others have an oncogene in the place of one of their normal genes.

Upon integration, the provirus can constitutively express the oncogene
How does activation of an oncogene by insertional mutagenesis with a retrovirus work?
Integration of a retrovirus can activate a downstream or upstream oncogene via a promoter or enhancer contained within the provirus.

***The virus does not have to be inserted upstream
What is Rb?
The retinoblastoma gene, binds to EF2 and inhibits G1/S progression of the cell cycle
What virus interferes with Rb, and what protein does it use to do so?
Adenovirus creates protein E1A that binds to Rb, allowing the cell cycle progression through G1/S
What is p53, and how does it work?
A transcription factor that controls expression of genes regulating cell cycle progerssion.

p53 is induced by DNA damage, and arrests the cell cycle in G1 to facilitate DNA damage repair prior to replication. If damage is unable to be repaired, p53 cause apoptosis.

In humans, p53 is mutated in at least 50% of cancers
How do Hepatitis C and Papilloma interfere with p53 function?
Hepatitis C produces a protein that binds to p53 and prevents it from binding to DNA, thus allowing replication to proceed.

Papilloma produces a protease that degrades p53, thus allowing replication to proceed.
What is the difference betwee RNA and DNA tumor viruses?
RNA tumor viruses activate oncogenes

DNA tumor viruses inactivate tumor suppressor genes.
What are endogenous retroviruses?
Exist as an integrated state in the DNA of the host cell.

Are inherited.

The cells don't produce a virus unless exposed to signals that can activate the virus, such as radiation, mutagens, or hormones.

Do not cause oncogenic transformation and do not carry oncogenes.
What are exogenous retroviruses?
Infest the host from the outside.

Some are tumorigenic.
What are rapidly transforming viruses?
Cause tumors within 2-4 weeks (sarcomas, leukemias, carcinomas)

Carry oncogenes

Most of them are replication-defective viruses. They acquired and oncogene that replaced genetic information of the virus. The exception is the Rous Sarcoma Virus

Can transform tissue culture cells as well
What are slowly transforming viruses?
Long latent period, the tumor appears months or years after the infection.

They do not carry oncogenes
What is a Cis-activating retrovirus?
The retrovirus integrates the provirus near a c-onc and activates it.

This occurs in Avian leukemia virus that integrates near c-myc
What is a trans activating retrovirus?
A virus gene encodes a transcriptional activator, and activates cellular genes elsewhere in the genome

Integration near a proto-oncogene is a rare event. Usually there is a long latent period, and additional mutations are required.

Slowly transforming viruses don't transform cells in tissue culture.
What is it called when virus gene encodes a transcriptional activator, and activates cellular genes elsewhere in the genome?
A trans acting retrovirus
What are the two types of Slow transforming viruses?
Cis-activating retroviruses
Trans activating retroviruses
What is the cause of ATL?
Adult T cell Leukemias/Lymphomas

HTLV-1 - Human T Cell Lymphotropic Virus
What is the classification of HTLV-1?
Trans-activating (slow transforming) virus.

**Tax - the viral transactivator, required for viral replication, and may cause activation of cellular genes (e.g. NFkB)

Transgenic mice that contain HTLV-1 Tax expressed from the viral promotor developed mesenchymal tumors.
What is Tax, and where is it found?
Tax is the viral transactivator in HTLV-1 (Human T Cell Lymphotropic Virus). It is an oncogene
What areas have HTLV-1 disease?
Japan, Carribeans, Middle Africa
How is HTLV-1 transmitted, and what is the chances of developing a disease out of it?
From mother to baby through breast feeding
By blood transfusions
Needles
Sexual Intercourse

After 20-40 years, 0.1% of carriers develop ATL
What is the link between HTLV-1 and ATL?
The virus is a co-factor and is responsible for only one of the stages in cancer development. Other factors are required.
How does HTLV-1 integrate into the genome, and how does it affect neoplastic transformation?
HTLV-1 integrates into a provirus at random chromosomal locations, but in all cells of a specific tumor the provirus DNA is integrated at the same site, generating a **monoclonal tumor**
What is different about the oncogenes of DNA viruses compared to RNA viruses?
The oncogenes of DNA tumor viruses are required for viral replication, whereas in RNA viruses they are not.
How do DNA tumor virus oncogenes work?
They bind cellular regulators and affect their activity.

They rarely produce tumors in their natural hosts.

However, DNA tumor viruses associated with human tumors are all human viruses
What are the five families of DNA tumor viruses?
1) Papovaviruses
2) Adenoviruses
3) Herpesviruses
4) Hepadnaviruses
5) Poxviruses
What is the natural host of Papova SV40 viruses? Where do they cause neoplastic transformation? How do they affect humans?
The natural host is monkeys

They cause tumors in rodents. Polyoma replicates in mouse cells, and causes tumors in newborn mice

First polio vaccines were contaminated with SV40. SV40 genomes were found in brain tumors
What is HPV, and what strains are important?
Human Papiloma Virus, a DNA tumor virus.

Around 50 strains, that cause benign and malignant tumors in animals and humans.

In humans, warts on hands, genitals, larynx, etc.

***Strains 16 and 18 are considered high risk for cervical carcinoma, which appears decades after the initial infection.
What are the likely co-factors that cause cells infected with HPV to become cancer?
~Smoking
~Co-infection with Herpes Simplex virus type 1 or 2
~Sexual intercourse with multiple partners
~The HPV oncogenes (E6, E7) inactivate pRb, p53
What is the evidence for a link between HPV infection and cervical carcinoma?
1) Positional link between areas of HPV infection and neoplastic transformation
2) HPV early proteins (E6, E7) found in neoplastic biopsies
3) HPV DNA strains 16 and 18 are found in cervical carcinomas. The viral DNA is episomal normally, but in tumor cells there are integrated copies in the chromosome.

***In 93% of cervical carcinomas there is evidence for presence of HPV
What diseases do the Herpesviruses cause in chickens and humans?
Marek Disease in chickens, a lymphoproliferative disease.

Herpes Simplex 2 has a connection with cervical carcinoma
What is the connection between Herpes Simplex 2 and cervical carcinoma?
1) There is no known oncogene in Herpes Simplex 2, but it is observed that women who have genital herpes develop cervical carcinoma with a higher frequency then women in control groups

2) Women with cervical carcinoma have a high titer of antibodies to the virus

3) Herpesvirus DNA was found in cervical carcinoma cells, but not in cells from a normal tissue
What causes infectious mononucleosis?
Epstein-Barr virus (EBV)
What disease does EBV cause?
In developed countries causes infectious mononucleosis.

It infect B-lymphocytes.

There is an established link between EBV and Burkitt's lymphoma in children in central africa.

There is a link between EBV and nasopharyngeal carcinoma, particularly in males in China.

**No link has been found between EBV and sporadic cases of Burkitt's lymphoma outside of Africa
What is the pathogenesis of EBV induced Burkitt's Lymphoma in Africa?
EBV exists as an episome in all cells, and does not produce virus.

All cells express EBNA1, early EA, VCA, MA, but ***do not*** express EBNA2, LMP that can be recognized by T-cells.

***Infection of B cells with EBV causes cellular immortalization

In malignant cells, there are typical chromosomal translocations, 8:14, 2, 22. The c-Myc gene is brought near the immunoglobulin locus.

There are additional p53 mutations.
What is the typical chromosomal translocation associated with EBV Burkitt's Lymphoma?
8:14
What are the three stages that George Klein suggested that Burkitt's Lymphoma develops in?
1) EBV infection leads to enhanced cellular proliferation
2) Environmental factors - malaria infection inhibits T-cell action against infected cells
3) Chromosomal translocations that activate c-Myc
What virus is associated with Kaposi's sarcoma?
Human Herpesvirus 8 is found in these tumors at a high frequency, and is believed to have a role in induction of the tumor.
What is the mechanism of oncogenic transformtion in Kaposi's sarcoma?
The mechanism by herpesvirus is unclear.

EBV has a gene (EBNA) that is a suspected oncogene, but transformation of cells in cultures occurs at a very low frequency.

It is believed herpesvirus contributes to one stage of the tumorigenic process.
What do Pox viruses cause in humans?
Benign tumors, by an unknown mechanism
What is a likely candidate for Pox viruses ability to cause tumors in humans?
They have a gene encoding a growth factor that has similarities to EGF and TGF, which may play a role in transformation.
What disease is associated with HBV?
Hepatitis B virus

High risk for developing hepatocellular carcinoma (HCC) in humans.

Carriers have a 200-fold higher risk of developing HCC
What are the characteristics of HBV diseases?
Carriers have a 200-fold higher risk of developing HCC.

Long latent period of 20-40 years.

In 80% of HCC cases, integrated viral DNA is found
What is the oncogenic process of HBV induced HCC?
Oncogenic process is unclear, though it is suggested that viral replication over a long period of time (chronic infection state) can induce inflammatory reaction and release of oxidants that cause DNA damage.

Oxidative damage requires enhanced liver proliferation of hepatocytes, which enhances the accumulation of mutations.

HBX is a trans-activator of viral and cellular promoters. It works by interacting with cellular transcription factors, amongst other mechanisms.
What is HBX, and how does it work?
A viral protein encoded by HBV that is suspected at playing a role in development of HCC.

HBX is a trans-activator of viral and cellular promoters. It works by interacting with cellular transcription factors.

It also causes cellular proliferation and inhibits apoptosis (binds p53)

It interacts with the cellular DNA damage repair system, and delays or prevents damage repair, causing accumulation of mutations.

HBV, with its X gene, causes genetic instability at the site of integration (duplications and translocations)
What are additional factors and elements regarding HCC?
Carcinogens and alcoholism are environmental factors that increase likelihood of HCC.

Some evidence that HCV also causes cancer.

An effective vaccine against HBV would prevent HCC.
What are the problems with proving that a human cancer is caused by a specific virus?
~Long latent periods
~Viral infection being only one stage ina multi-stage process (chromosomal changes, chemical carcinogens, additional mutations, etc.)
What are the 5 major problems with proving a human cancer is caused by a specific virus?
1) It is not possible to test involvement of a virus by transfer from one individual to another (Koch's postulate).
 
2) The viral genome may not necessarily stay in the tumor: it may have contributed at an early stage and then disappeared.
 
3) A virus can be found in a tumor, but be there because the tumor cells facilitate its replication, and not because it is essential for tumor development.
 
4) Circumstantial evidence: testing transformation of cells in tissue culture or tumorigenesis in laboratory animals.
 
5) The best evidence would be: developing effective vaccines against viral infection and find that it also inhibits appearance of tumors.
What viruses mostly target the respiratory tract?
Influenza
Parainfluenza
RSV
When was the first pandemic of influenza described?
1580
What two findings led to the development of inactivated vaccines for Influenza?
1) Influenza virus can be cultivated in embryonated eggs

2) Hemagglutination is discovered
What are the rates of epidemics and pandemics for Influenza?
Epidemics every 1-3 years

Pandemics every 10-20 years
What are the internal antigens of Influenza?
NP, M
There is cross-reactivity within the group.
There is no cross reactivity between the groups.
What are the external antigens of Influenza?
NA, HA
Division into subtypes based on the antigenic properties of HA (16), and NA (9) in Influenza A
How is Influenza named?
***A, B, or C = major subtype, classified based on NP antigen

Country of Origin

Strain Number

Year of Isolation

HA

NA

All in that order
What are the natural hosts for Influenza types A, B, and C?
A - Humans, horses, pigs, birds, etc.
B - Humans
C - Humans, pigs
How is the Influenza genome encoded? How does this breed antigenic diversity?
Genome is in 8 segments (7 in C strains) of ssRNA.

Reassortment after replication creates new antigenic strains.
How do birds spread Influenza?
In their droppings
What is different between Antigenic shift and drift in Influenza?
Drift is small accumulated mutations in one strain.

Shift is dramatic change to antigenic composition from reassortment of genes of different strains.
What is the target of neutralizing antibodies in Influenza?
HA, not NA
What are the three major Influenza pandemics of the last century?
1918 - H1N1 "Spanish" flu
1957 - H2N2 Asian
1968 - H3N2 Hong Kong
What gives rise to Pandemic strains of influenza?
Genetic reassortment between different strains (antigenic shift)
Who is the chief distributor of Influenza in the populations?
School children
Who has the highest morbidity for Influenza?
Preschool age children and old people
What causes systemic signs in Influenza patients?
The result of disintegrated infected cells
What are the complications of Influenza infection?
Mainly in the lungs - primary influenza viral pneumonia mainly in high risk groups.

Secondary bacterial pneumonia is also well-recognized: biphasic illness
Antibodies against what are the most important in protecting against Influenza?
HA

Antibodies to NA may help reduce severity of disease
Changes in HA result in what?
No immune protection in previously exposed hosts
What are the most important Ig's for Influenza infection? What is their timeline?
Secretory IgA in nose and airways, and local IgGs are more important then circulating IgGs.

Local antibodies appear shortly after infection, peak at 14-21 days, and ***disappear fast***.
What is the Influenza vaccine?
A mixture of strains that were prevalent in the previous year.

Preparation is from infected embryonated eggs or tissue culture, then inactivated with formalin.

Efficacy is 70%
When should the Influenza vaccine be given?
To people in high risk groups, every 1-2 years in the fall.
What drugs are Neuraminidase inhibitors?
Oseltamivir
Zanamivir
What drugs are given for Influenza A infections when its not advisable to vaccinate?
Amantadine or Rimantadine
What type of virus is Influenza?
Orthomyxovirus
What are paramyxoviruses?
Negative ssRNA viruses
Unsegmented - no antigenic shift
What are the two surface glycoproteins on Paramyxoviruses?
HN - has both hemagglutinin and neuraminidase activity

F protein - mediates cell fusion, causes apperance of giant cells and facilitates cell-to-cell spread of the virus.
What is the main clinical symptom of Paramyxoviruses that leads to hospitazlization?
Laryngotracheobronchitis - Croup - respiratory difficulty and a harsh cough
What are the 4 parainfluenza strains?
Type 3 - mainly in infants
Type 1, 2 - in children
What is the transmission of Parainfluenza?
Aerosol and hand-to-nose
What is the treatment for parainfluenza?
Mostly symptomatic. Today Ribavirin, a synthetic nucleoside is given by aerosol.
What is RSV?
Respiratory Syncytial Virus

The most important cause of lower respiratory tract illness in infants and young children.
What is the most important cause of lower respiratory tract illness in infants and young children?
RSV
What is the presentation of RSV?
Babies under 1 year of age - pneumonia, a severe disease

Older children - bronchitis, bronchiolitis, and upper respiratory tract infections

Adults - colds
What is the transmission and treatment of RSV?
Transmission by contact with contaminated hands or surfaces

Ribavirin treatment by aerosol in severe cases

Fast diagnosis available by IF, ELISA of nasopharynx secretions
What are the top 5 agents that cause the common cold?
1) Rhinovirus - Picorna viruses, over 100 serotypes, 20-45% of colds
2) Adenoviruses
3) Coronaviruses
4) Myxoviruses
5) paramyxoviruses
What is measles?
Belongs to Paramyxovirus family.

An enveloped, helical nucleocapsid.

ssRNA genome with negative polarity.

Encodes hemagglutinin and fusion protein (causing giant cell formation)

Infects humans and primates
How does measles progress?
Infection begins at the respiratory tract. Virus spread to lymphatic tissues, and then by viremia to other epithelial surfaces.

Incubation period of 10-14 days.

First clinical stage - fever and symptoms of upper respiratory tract infection, Koplik spots.

Later - rash, appearance of antibodies, disappearance of viremia
How is diagnosis of measles made?
Mainly serological. Increase in antibody titer, or identification of specific IgM antibodies.
How is measles prevented?
Attenuated live vaccine, gives a life-long protection. 95% efficient.

Given as MMR at age 12 months, and a boost at 6 years.
What is MMR?
Measles
Mumps
Rubella

A mixture of live attenuated vaccines.

Given at 12 months, and a booster at 6 years.
What are the complications of measles?
1) Pneumonia
2) Encephalitis, probably caused by an autoimmune reaction
3) Myocardial damage
4) Increased mortality linked to malnutrition. Measles is one of the leading causes for mortality of children in third world countries.
What is SSPE?
Subacute Sclerosing Panencephalitis

A rare degenerative disease of the nervous system, caused by a persistent latent infection of the brain by the Measles virus.

CSF contains a high titer of antibodies to measles.

Occurs 5-15 years after the measles infection. Can also be caused by the attenuated vaccine (lower frequency)
What disease occurs as a result of a persistent infection of measles in the brain?
Subacute Sclerosing Panencephalitis (SSPE)
What is the main clinical symptom of Mumps?
Parotitis, though 30% of infections are subclinical
What are the additional symptoms of Mumps, aside from Parotitis?
Aseptic Meningitis
Meningoencephalitis
Orchitis (mostly in post-pubescent age)
Pancreatitis
Thyroiditis
Myocarditis
Ovarian Infections
How is diagnosis of mumps made?
Isolation of the virus from saliva, urine, CSF - identification by hemadsorption

Serological test - Increase in antibody titer, or identification of specific IgM
How is Mumps prevented?
MMR live attenuated vaccine

Given at 12 months and boost at 6 years
What are the various outcomes of viral infection?
1) Asymptomatic
2) Acute infection - disease
3) Chronic disease
4) Cancer
5) Slow neurological disease
What are inapparent infections?
Infections without clinical manifestations

They are of high prevalence, and high epidemiological importance
What are the factors affecting the outcome of a viral infection?
1. Number of infecting virions
2. Viral virulence
3. Transport of virions to susceptible cells.
4. Effect of infection on cellular functions
5. Speed of viral replication and spread in the body
6. Host response
What is the virulence of a virus?
The ability of the virus to cause a disease.
What are the genetic determinants of viral virulence?
Viral genes that promote the efficiency of:

Viral replication
Host injury
Viral transmission
Access to target cells
Escape from immune response
Production of ***virokines - viral products which interfere with the immune response
Where does the wild type and attenuated type of Polio virus replicate?
Wild Type - replicates in human intestinal epithelia and neurons

Attenuated virus - replicates in intestinal epithelia but NOT neurons
What are the modes of viral transmission?
Direct contact - hands, sexual
Indirect - food, fomites, injection
Airborne
Vertical
What are the stages in viral infection?
1) Entry into host and local replication
2) Systemic Infection
3) Localization of virus in target organ
4) Virus release from host
What are methods of viral penetration into the host?
1) Respiratory system
2) Digestive system
3) Genitourinary system
4) Skin - by sting, bite or needle stick
How does a virus develop a systemic infection?
1) Via lymph and blood stream
2) Via blood cells
3) Cell to cell
What is viremia?
Presence of the virus in the blood. The virus may be free int he plasma, or cell associated.

Viremia may be primary or secondary
What is primary viremia?
Viremia that brings the virus to internal organs for further replication
What is secondary viremia?
Viremia that is long lasting, with large quantities of virus. Brins virus to target organs
What is tropism in regards to a virus?
Specifying where the virus will target for infection, i.e. dermatotropic, neutrotropic, pneumotropic, enterotropic, etc.
What causes the clinical presentation in viral infection, and what mediates it?
Clinical presentation = Cellular injury

Injury is caused by viral replication or immune response
What are the incubation periods for different viral infections?
Incubation period is time between infection and clinical symptoms

1) 1-3 days for local infections
2) 10-20 days for systemic infections
3) Some viral infections have very long incubation periods, months to years.
What is the difference between a latent and chronic viral infection?
A latent infection produces periodic clinical manifestations, with latent periods without viral replication

A chronic infection is persistently producing virions
What are the non-specific forms of host resistance to infection (physiological factors)
Host species
Age
Hormones
Nutrition
What are the modes of host defense against infection?
1) Natural barriers - skin, low pH
2) Innate immune response - INF, NK, Macrophage, Cytokin
3) Specific immune response - cell mediated (CD8), humoral (Ig)

Viruses are good immunogens
What are the antibodies of specific immune response?
IgM - early
IgG - late, persists
IgA - mucous
What are the modes of action of antibodies against viruses?
1) Neutralization of viruses - prevent adsorption and penetration into cell
2) Cell lysis in presence of complement - in budding viruses, when viral proteins are present in the cell membrane
3) Antibody dependent cell mediated immunity. Activation of killer cells by Fc receptors
4) Antibodies which cover the virus particle serve as opsonins - phagocytosis and destruction by macrophages
What mediates cellular immunity?
CD4 and CD8 T cells
What form of immunity is part of the recovery process from viral disease?
Cell mediate immunity.

Role of Humoral mediated immunity in recovery is unclear - Agamaglobulinemia
What is Agamaglobulinemia?
No production of antibodies because of B lymphocytes malfunctioning - proper recovery, frequent infections
What does immunity depend on in a systemic viral infection?
Sufficient amount of antibodies
How does the immune response contribute to the pathogenesis of disease?
1) Destruction of cells presenting viral peptides on their surface - tissue damage associated with clinical symptoms
2) Immune complex mediated damage
3) Autoimmunity
What are short and long term immunity?
Short term immunity - Local infections with short incubation periods. Various viruses associated with the same clinical symptoms. Frequent antigenic change sin the causative viruses. Examples - common cold, influenza

Long term immunity - Viruses that cause viremia, long incubation time, stable antigenic composition. Examples - measles, mumps, varicella, polio, etc.
What are the three modes of activate immunization?
1) Live attenuated virus
2) Killed virus
3) Antigenic components of the virus produced by genetic engineering or by chemical methods
What is Passive immunization?
Administration of immune serum globulin, either total or specific.

In nature - transfer of antibodies from mother to fetus
What are the types of immunization?
Active - antigenic components provided to develop long term memory response

Passive - preformed Ab's given in immune serum globulin
What are routine immunizations?
Polio - live vaccine, killed vaccine. Several doses of vaccine in childhood.

Measles, Mumps, Rubella - MMR - Live vaccine, given at 12 months and booster at 6 years

HAV - Immunization at 18 months
What are the characteristics of the Herpes virus?
Family: Herpetoviridae
Size - 180-200 nm

1) Nucleocapsid
~Icosahedron capsid - protein
~Large ds DNA, encodes 60-80 proteins

2) Envelope - contains lipids that originate at the ***cell nucleus***

3) Tegument
How and what type of infection do herpes viruses produce?
All herpes viruses persist in the host in latent infection.

Herpes viruses code virokines and immune escape proteins that interfere with immune response, antigen presentation and apoptosis of infected cells.

***Cell mediated immunity important for controlling the infection
What are the 8 Human Herpes Viruses?
1) Herpes simplex type 1 (HSV-1)
2) Herpes simplex type 2 (HSV-2)
3) Varicella-Zoster virus
4) Epstein-Barr virus
5) Cytomegalovirus
6) Human Herpes virus 6 (HSV-6)
7) Human Herpes virus 7 (HSV-7)
8) Human Herpes virus 8 (KHSV)
What are the predominant infections of HSV-1 and HSV-2?
HSV-1 - Perdominantly orofacial infections. Internal organ infections in immunocompromised hosts. Herpes encephalitis.

HSV-2 - Predominantly genital infections. Most neonatal infections.
What is the epidemiology of HSV?
High prevalence world wide

High percentage of the population has recurrent infections (20-40%). Source for infection of susceptible individuals.

Many new genital herpes infections each year and millions with recurrent infections

In nature, man is the only reservoir
What are the primary infections of HSV?
1. Individuals without antibodies
2. Mostly in childhood
3. Often asymptomatic
4. May present a severe form
5. Virus penetration to epithelial cells. Virus replication and cell lysis.
6. Following primary infection - virus migration via sensorial nerves to regional ganglia.
7. Establishment of latent infection
8. 4-8 days post infection HSV antibodies are present. Antibodies do not prevent reactivation
What is the role in neurons in HSV-1 infection?
Following a productive infection, virions enter the neurons and move by retrograde transport to the ganglia.

Reactivation causes the virion to move by anterograde transport, back out of the neuron at the synapse.
How does recurrent infection of HSV-1 occur?
1) Infection in individuals with antibodies
2) Reactivation of latent infection
3) Migration of virus from ganglia to external area
4) Asymptomatic infection or lesions
5) Mostly milder symptoms
6) Infection with another type - possible
What factors are associated with reactivation of laten HSV-1?
1) Fever (fever blisters)
2) Hormonal changes
3) Stress
4) Exposure to sun (UV)
What are the clinical manifestations of orofacial HSV-1 infections?
Mainly in childhood, mostly asymptomatic.

Rarely severe complications, such as stomatitls, pharyngitis, many facial lesions.

Reactivation - mainly in the same region.

Stages of disease - red swelling, sensitivity, blister, crust.
Genital infection by HSV is mainly caused by what strain?
HSV-2
What are the differences in primary and recurrent genital infection by HSV-2?
Primary infection - Systemic symptoms, prolonged disease with virus excretion

Recurrent infection - Less severe, shorter period of virus shedding
What is herpes encephalitis
A very serious disease with 70% mortality if not treated in time. A very rare disease.

Clinical symptoms - headache, fever, behavioral changes, focal convulsion.

Infection mainly of the temporal lobe.

Treatment is with acyclovir.

Diagnosis by PCR.
What causes neonatal HSV infection, and how can it be prevented?
Occurs during delivery in a mother with active genital HSV infection at the time of birth. Severe infection of the newborn with high mortality rate.

Prevention by identifying mothers with active infection and C-section delivery
What occurs in HSV ocular infections?
Mainly herpes keratitis.

Both primary and recurrent infections. Invasion of the inner eye and blindness possible.
What occurs in HSV infection of immunocompromised hosts?
Disseminated severe infection.
Ulcerated lesions.
Invasion of visceral organs.
How is laboratory diagnosis of HSV performed?
1) Serological testing - limited value
2) Isolation of virus from infected tissue
~Identification of cellular changes CPE
~Final identification by specific antibodies

3) Direct identification of viral antigens (EIA, Immunofluorescence)

4) Direct identification of viral DNA by PCR
What causes chicken pox?
Varicella-Zoster virus (VZV)
What is the primary infection of VZV?
Chicken pox - mild disease - fever and vesicular rash. Secondary bacterial infection of lesions.

**Severe disease in neonates, patients with malignancies, or immune suppressed.
What is the recurrent infection of VZV called?
Herpes Zoster - reactivation of the virus, mainly in elderly people or immunocompromised patients.

Vesicles along the nerve fiber that is reactivated.

Severe pain results from damage to sensory nerves
What is the pathogenesis of VZV?
Infection by respiratory route of contact

Extremely contagious virus

Systemic infections by viremia

Most infections are symptomatic
How is VZV diagnosed?
Acute infection - IgM
Immunity - IgG
Isolation of virus from vesicular fluid or respiratory secretion
PCR of DNA from CSF, vesicular fluids or respiratory specimens
How is VZV prevented?
Passive Immunization - Pregnant women, leukemic children

Active Immunization - Attenuated live virus
What disease does EBV cause?
***Infectious mononucleosis

Also fever, lymphadenopathy, hepatitis, respiratory symptoms.

Rarely CNS damage.

In peripheral blood produces atypical lymphocytes
How does infection with EBV occur?
What is the incubation period?
What are the clinical symptoms?
Spread - Close contact via saliva
Incubation - 30-50 days
Clinical symptoms - Most infections in childhood are asymptomatic. In adolescents and young adults - Infectious Mononucleosis
What does EBV infect?
B lymphocytes - mainly produces a latent infection. Only some viral antigens are produced - EA, EBNA.
What is the EBNA antigen?
Produced in B lymphocytes infected with EBV

Immortalization of B lymphocytes as a result of EBV infection.
In what disease are B-cells immortalized?
EBV infection
What do the viral antigens on B-cells caused by EBV infection result in?
T-cell proliferation - ***Atypical lymphocytes
B-cells produce antibodies - ***heterophil antibodies
How is the diagnosis of EBV made?
For primary infection:
Detection of IgM antibodies to VCA or EA

VCA - Viral Capsid Antigen
EA - viral Early Antigen

For Past Infections:
IgG antibodies to EBNA antigens
IgG antibodies only
What malignancies is EBV associated with?
1) African Burkitt's Lymphoma
2) Nasopharyngeal Carcinoma
3) Lymphoproliferative disease in immune suppressed individuals
What does CMV cause in fetuses?
In fetuses, may cause congenital malformation.
What does acute infection of CMV present as?
Asymptomatic, mononucleosis, hepatitis, respiratory infection.

Latent infection in leukocytes and epithelial cells in kidney, glands, and other organs.

May be transmitted by transfusion and transplantation
What type of transplantation does CMV infection occur in?
Kidney transplantation
Bone marrow transplantation

Latent CMV may be present in transplanted organ (only from a donor with CMV antibodies). The virus can be reactivated in the recipient and cause severe disease.
How is diagnosis of CMV made?
1) Virus Isolation - in cell culture, specific identification of antibodies
2) Serology - in primary infections identification of IgM antibodies. In recurrent infection a rise in titer of IgG antibodies
3) PCR - identification of CMV DNA in body fluids, lymphocytes, etc.
4) pp65 antigenemia - detection of CMV antigen in peripheral leukocytes by monoclonal antibodies - viremia
What is therapy for CMV?
Both CMV and EBV are ***NOT affected by acyclovir

In severe CMV infection, treatment with Gancyclovir or Valgancyclovir. ***A drug with higher toxicity.
What are the different hepatitis viruses, and how are they transmitted?
HAV - Enteric Transmission
HBV - Paraenteral Transmission
HCV - Paraenteral Transmission
HDV
HEV - Enteric Transmission
HGV - Paraenteral Transmission
What to hepatitis viruses infect?
In nature - human infection only.

Infects only primates.

Because of this, most viruses cannot be grown in cell cultures.
How is most information about hepatitis gained?
Immunoassays
Electron Microscopy
Molecular Virology
What are the clinical manifestations of viral hepatitis?
1) Asymptomatic infection
2) Unicteric hepatitis
3) Icteric hepatitis
4) Fulminant hepatitis - Severe hepatic failure, pronounced jaundice, encephalopathy, high mortality rate

Rate of infection determined by seroepidemiological surveys. Large proportion of asymptomatic infections.
What are the stages of viral hepatitis?
1) Preicteric period - 5-10 days prior to appearance of jaundice. Fever, nausea, loss of appetite, gastrointestinal symptoms.

2) Icteric period - several weeks, dark urine, pale stool, jaundice

3) Convalescence
What is hepatitis A?
Previous name - infectious hepatitis

A Picornavirus
Diameter - 27 nm
ssRNA (+)
Non-enveloped
A large precursor protein that is proteolytically cleaved into small proteins (structural proteins VP1, VP2, VP3, VP4)
What are characteristics of Hep A disease?
Fecal-oral infection. Fecal excretion of virus at end of incubation period and beginning of clinical stage. Wide spread in poor sanitary conditions and crowding.

Incubation of 15-45 days.

Very stable virus.

Disease more severe in adults.

Serum antibodies seen at outset of clinical symptoms.

Clearance of the virus and immunity for life, with no chronic infections.
What is the HAV epidemiology.
Global distribution.

Childhood, mainly asymptomatic infection in developing countries.

In developed countries, many non-immune adults.

Rise in socioeconomic status = less infections at young age.

**High prevalence in mediterranean area.

In Israel, different epidemiological patterns in various populations
How is a laboratory diagnosis of HAV made?
IgM anti-HAV in serum.
How is HAV prevented?
1) Passive immunization (Immune serum globulin ISG)
2) Active immunization - inactivated vaccine
What is Hepatitis B?
Historically - Post-transfusion hepatitis (PTH)
Causes acute and chronic liver disease

d.s. DNA genome
DNA polymerase
Capsid (core) Hepatitis B core Ag
HBcAg
HBeAg
Enveloped
Hepatitis B surface antigens - HBsAg
What are Hepadnaviridae?
A number of animal viruses similar in structure and properties to HBV.

All of them cause acute and chronic liver disease.
How does HBV replication proceed?
Penetration of host cell and DNA release.

Transcription: mRNAs, pregenome RNA

The core proteins encapsulate the pregenomic RNA

Reversed transcription: Synthesis of viral DNA.

***Reversed transcription in a DNA virus - ONLY IN HEPADNAVIRUSES

HBsAg is produced in large excess. It is easy to identify by immunoassays. Serves as a marker for the presence of HBV.
How is HBV transmitted?
1) Paraenteral infection: Blood and blood products, needle sticks, sharp tools (medical personnel), syringe sharing (drug users) and in medical institutes w/o proper sterilization

2) Sexual transmission

3) Mother to offspring
What is the progression of HBV disease?
Prolonged incubation period of 1-5 months.

Asymptomatic infection - frequent

Acute symptomatic hepatitis in parts of the infections

Chronic infection: 5-10% of adult's infections. 90% of infants.
What are the aspects of HBV chronic infection?
1) Mostly asymptomatic
2) Chronic active hepatitis
3) Cirrhosis
4) Primary hepatocellular carcinoma

More then 300 million carriers worldwide, mostly in Africa and Asia.

Percent of carriers in the population vary in different countries.
How is a diagnosis of HBV made?
Identification of HBsAg in serum - HBV infection:

Presence of IgM anti-HBc = acute infection
Abscence of anti-HBc = chronic infection
The presence of IgM anti-HBc indicates?
HBV acute infection
What is the serological marker for HBV vaccination?
anti-HBs
What are the serological markers for acute, carrier, and past infection of HBV?
Acute - HBsAG +, anti-HBS -, anti-HBC -

Carrier - HBsAG +, anti-HBS -, anti-HBC -

Past Infection - HBsAG -, anti-HBS +, anti-HBC -
Identification of what in a patient is indicative of active replication of HBV?
HBV-DNA

BY dot blot hybridization, PCR, quantitative PCR
Identification of HBV-DNA in serum is an indication of what?
Active replication of the virus
How is HBV prevented?
1) Identification of blood units positive for HBsAg - ***Obligatory testing

2) Active immunization - high risk population or universal. Vaccine:

a. Purified HBsAg
b. Recombinant HBsAg

Since 1992 universal immunization of all newborns in Israel

3) Passive immunization - Hepatitis B Immune Globulin (HBIG) given immediately after exposure

4) Passive - Active immunization
What is HDV?
Delta Hepatitis or Delta Virus

Infections by HDV is **ALWAYS** associated with HBV infection.

It is an incomplete virus that replicates only in the presence of HBV
What does HDV require for establishing infection?
Co-infection by HBV, because HDV is an incomplete virus
What are the characteristics of HDV?
ssRNA (-) virus
Capsid - delta Ag
Envelope - HBsAg
What is the difference between co-infection and super-infection of HDV? Which is worse?
Co-infection - Occurs simultaneously with HBV

Super-infection - Infection in HBV carriers


Super infection is worse
What is the most important cause of PTH?
Post transfusion hepatitis

HCV
What is HCV the most important cause of?
PTH - Post Transfusion Hepatitis
What are the characteristics of HCV?
ssRNA (+)
Enveloped
Icosahedron

Enveloped RNA virus related to Flaviviruses

6 different genotypes, prevalent in various geographic regions
Who is HCV infection prevalent amongst?
1) Receivers of transfusion blood and blood products
2) IV drug abusers
3) Dialysis patients
4) Patients with chronic liver diseases.

The rate of infection among health care workers is low.
How is HCV transmitted?
Blood - primary
Sexual - low
Mother to child - low
What are the characteristics of HCV hepatitis?
Most infections are asymptomatic, with incubation time of 6-8 weeks.

Acute hepatitis mostly occurs post-transfusion.

A large proportion of infections become chronic - 85%

There is a strong associate with chronic liver diseases

Alcoholism, infection at older age, and male gender all = worse prognosis
What factors equate to a worse prognosis for HCV?
Alcoholism
Infection at old age
Male gender
How is HCV diagnosis made?
1) Testing for anti HCV antibodies mostly by EIA. The presence of antibodies is in most cases an indication for an active HCV infection.

2) Identification of viral RNA in the serum by RT-PCR - viral replication

3) Quantitative RT-PCR - Viral load, monitoring, response to therapy
The presence of what diagnostically means active HCV infection?
anti-HCV antibodies
Viral replication is diagnostically observed in HCV by?
RT-PCR
How is Viral load, monitoring, and response to therapy in HCV diagnostically done?
Quantitative RT-PCR
what is HEV?
Hepatitis E Virus

s.s. RNA (+)
Icosahedron
Non-enveloped
What is the epidemiology, transmission, and initial diagnosis of HEV?
1) Associated with epidemics
2) Transmission by fecal-oral route. Associated with contaminated water
3) Mode of transmission similar to HAV
4) Viral RNA was identified by molecular methods
What are important dates in the history of HIV and AIDS?
1981 - First description in San Francisco and New York, a disease of homosexual men

1982 - Similar disease in IV drug abusers, hemophiliacs, transfusion recipients

1983 - L. Montegnier, Franco, isolation of virus called LAV

1984 - R. Gallo, USA, isolation of virus called HTLV3

1987 - HIV-2
What are the characteristics of HIV?
Exogenic retrovirus
Uses cellular receptor CD4
s.s. RNA (+) Genome
Reversed Transcriptase
Enveloped

Lab growth - lymphocytes or cell lines of T-cell origin.

In cultured cells, CPE.
What are the 3 major genes of the HIV genome?
Gag - responsible for synthesis of core proteins

Env - responsible for synthesis of envelope proteins

Pol - responsible for synthesis of reversed transcriptase helicase integrase

Additionally, regulating genes are - tat, nef, vif, rev, etc.
What types of proteins are gP120 and gP41?
Env proteins of HIV

gP120 - extends outside
gP41 - trans-membrane
What is the most important Pol protein of HIV?
Reversed Transcriptase Helicase Integrase
What are the two types of HIV, and where are they prevalent?
HIV-1 - in most European, American, and African countries. Subtypes a, b, c, etc. in different geographic areas

HIV-2 in West Africa and some European countries. About 50% similarity between the two types.

HIV-0 - East Africa

Frequent antigenic changes in HIV - apperance of new strains. Antigenic similarity between strains.
What HIV01 subtype is prevalent in North America?
b
How does viral replication of HIV proceed?
1. Binding to CD4 and co-receptors
2. Membranes fusion
3. Penetration
4. Uncoating
5. Synthesis of provirus
6. Provirus integration
7. Synthesis of protein precursors
8. Cleavage of precursors protein
9. Assembly
10. Budding
How do gP120 and gP41 mediate HIV fusion?
gP120 binds to CD4. This triggers a conformational change, and a different region of gP120 binds to CCR5 (monocyte).

gP41 then changes conformation, and binds to a fusion domain.

The virion envelope then fuses with the cell membrane, release the nucleocapsid into the cell
How are individuals infected with HIV identified?
Identification of anti-HIV antibodies = infected individual

Antibody Assays:
Screening - mainly by ELISA
Confirmation - Western Blot

1) Virus isolation from lymphocytes or other cells
2) Identification of viral antigen (mainly p24) in serum or body fluids
3) Identification of viral nucleic acid - RT-PCR, PCR
How is HIV transmitted?
1) Sexual transmission
2) Blood borne transmission
3) Mother to infant/embryo
~Intrauterine
~At the time of delivery
~Via breast milk
Presently, what is responsible for most HIV infections?
Heterosexual sexual transmission
How does HIV spread and what are its target organs?
1) The first target cells are monocytes - macrophages and CD4 T-cells.

2) Dissemination to target organs through the blood: cell associated or free in plasma

3) Major targets are lymphoreticular organs and nervous system

4) Progressive damage to the immune system. Decline in the number of CD4 cells.

Reverse CD4/CD5 ratio
How does HIV produce nervous system infection?
HIV enters the brain through peripheral blood monocytes or plasma free virions

Damage to the brain is the result of cytokine secretion, viral proteins toxic to neural cells, direct cell destruction by the immune response

Brain damage caused by opportunistic infection
What is the immune response to HIV infection?
Both humoral and cell mediated:
~Neutralizing antibodies
~Antibody dependent cell cytotoxicity - ADCC
~Cytotoxic T Lymphocytes
How does HIV kill or injure CD4 cells?
Hypothesis:

Viral rpelication
Immune cytolysis
Accumulation of unintegrated proviral DNA
Increased cell permeability associated with viral budding.
Enhanced apoptosis
Induction of cell fusion events
Production of autoimmunity
What are the stages of HIV infection?
1) Acute primary infection. Symptomatic - mild or severe or asymptomatic
2) Latency, asymptomatic infection and persistent generalized lymphadenopathy
3) Symptomatic HIV infection
4) AIDS

HIV infection is a **chronic** infection
AIDS is a **lethal** infection
What are the clinical manifestations of HIV infection?
Chronic fevers
Night sweats
Diarrhea
Weight loss
Bacterial infections
Fungal infections
Parasitic infections
Viral infections
Malignant diseases
Wasting syndrome
Recurrent pneumonia
What malignancy is associated with HIV infection?
Kaposi's Sarcoma
What is the treatment for HIV/AIDS?
There is no therapeutic treatment. Treatment is designed to slow viral replication.

1) Inhibition of RT activity
~NRTI: AZT ddI 3TC, Tenofovir
~NNRTI

2) Protease inhibitors - inhibit activity of viral protease - required for cleavage of viral polyprotein precursors. Inhibit viral replication. used in combination with RT inhibitors.

3) E-inhibitors - fusion inhibitors, chemokine antagonists

4) Integrase inhibitor
~Slows the development of disease in **symptomatic patients**
~In **asymptomatic patients** with decline of CD4 cells, slows the development of symptomatic disease
What are problems associated with HIV treatments?
Resistant strains appear during treatment

Mutants with altered RT or protease

Serious side effects

Many different pills at different times

Poor compliance
What is the Western Pattern Epidemiology of HIV infection?
Risk Groups:
1) Homosexual men
2) I.V. drug abusers
3) Blood and blood products receivers - past
4) Sexual partners of above
5) Infants of infected mothers
6) Individuals with multiple sexual partners (prostitutes)

***Heterosexual transmission is responsible for most new infections

******Poverty is the most important risk factor (USA Blacks and Hispanics)
What is the most important risk factor for HIV acquisition?
Poverty (USA Blacks and Hispanics).

Low socio-economic status is associated with risk behavior
What is the epidemiology of HIV in Africa?
The central problem of the AIDS epidemic - recently together with Asia

Not associated with risk groups - 50% men, 50% women

Many childhood infections from infected mothers and from blood.

In parts of sub-saharan Africa, millions infected.

Some urban areas 30-40% infected of the 18-40 year old range.

Many AIDS orphans.
When and where has the AIDS epidemic in Asia been localized?
In the last 5-6 years, increase in number of infections and reported AIDS cases in Thailand and India
What is the epidemiology of HIV in South America?
Substantial spread, particularly in Brazil and Latin America. Not in traditional risk groups.
What are the important teratogenic viruses?
Rubella and CMV
Viral infections in pregnancy can present as?
1) Embryo uninfected
2) Embryo infection
3) Spontaneous abortion
What is the outcome of fetal viral infection?
1) Normal infant with antibodies
2) Death of fetus
3) Infant with congenital malformation - taratogenic effect
What are the most severe viral induced teratogenic defects associated with?
Infection at an early gestation age
How is a virus transmitted to the fetus?
1) Transplacental transmission during mother's viremia
2) Ascending infection
3) Invasive diagnostic procedure
4) During delivery
What causes the teratogenic effect?
Damage to fetal cells causing damage to developing organs

Placental damage
How will viral induced teratogenic defects be observed?
Some malformations are detected at birth.

Others, especially improper development, will be identified only later in life.
What are the characteristics of Rubella?
German measles
s.s. RNA (+)
Enveloped
Hemagglutinin
What are the clinical symptoms of Rubella infection?
1) Asymptomatic infection
2) Disease with rash 1-3 days
3) Incubation period 14-25 days
4) Enlargement of cervical lymph nodes
What is congenital rubella?
1) First diagnosed in 1941 by ophthalmologist Dr. N. Gregg, he described an association between cataracts in infants and rubella in the mother at the first trimester of pregnancy.

2) Most of information was gathered in large epidemics that occurred until the introduction of the vaccine.

3) most damage occurs when the mother is infected at the first trimester of pregnancy (early gestation age of infection = more severe teratogenic effect)
How is the diagnosis of Rubella made?
Many infections of children and adults are asymptomatic.

Clinical symptoms are NOT SPECIFIC. Clinical diagnosis is not enough.

Diagnosis of rubella infection required serological tests.
Lab tests:
1) Test for rubella IgG antibodies by ELISA - screening of woman at child bearing age - **status of immunity**
2) Acute infection - test for rubella IgM antibodies by ELISA
3) Infected embryo or infant - test for rubella IgM antibodies by ELISA
What are the characteristics of congenital infection of Rubella?
1) Infection at early gestation = many spontaneous abortions
2) Infection can occur at any stage
3) The fetus is infected when the mother has clinical or sub clinical infection
4) The earlier the infection - the more severe the damage
5) Prolonged excretion of the virus in infants with congenital infection despite the presence of antibodies
6) Infants have IgG antibodies (mother + infant) and IgM antibodies (***INFANT ONLY***)
In congenital infection with Rubella, who has IgM antibodies, and who has IgG antibodies?
IgM - Infant only
IgG - Mother and infant
In congenital infection with Rubella, what antibodies does the infant have? The mother?
Infant - IgG and IgM
Mother - IgG
What are the main malformations of congenital rubella syndrome?
Eyes
Large blood vessels and heart
Deafness
How is congenital rubella prevented?
Only by preventing maternal infection by IMMUNIZATION

Live attenuated vaccine MMR - given at 12 months and 6 years.

MMR - Measles, Mumps, Rubella

Possible revaccination of girls at puberty
What are the possible congenital infections of herpes viruses?
CMV or VZV - teratogenic potential
HSV - severe disease in neonate
EBV - no fetus infection
HHV-6 - no fetus infection
What is the most important teratogenic virus today?
CMV
What are the characteristics of congenital CMV disease?
Cytomegalovirus Inclusion Disease

1) Ocular damage
2) *****Damage to the CNS - microcephaly, brain calcification, encephalitis, motor abnormalities, physical and mental retardation, deafness, etc.
3) Hepato-splenomegaly
4) Delayed abnormalities
5) Prolonged virus excretion in urine and saliva
What are the characteristics of Fetal infection with CMV?
1) Most important teratogenic virus today
2) Most of the teratogenic effect in maternal primary infection. Reactivation in pregnancy is frequent
3) Not every maternal infection is associated with fetal infection
4) Not every fetal ifnection is associated with malformations 10%
5) Death of the embryo will occur in some of the fetal infections - most early in the pregnancy
How is the diagnosis of CMV infection in the mother made?
1) Virus isolation - urine, saliva in primary or recurrent infection

2) Serology:
~Seroconversion - primary infections
~Presence of IgM antibodies - mainly in the primary infection, but also in activation
~IgG avidity test:
Low avidity = primary infection
High avidity = past infection > 3 months
How is the diagnosis of CMF infection made in a newborn? In an embryo?
Newborn:
1) Isolation of virus from urine
2) IgM antibodies

Infected embryo:
1) Detection of virus in amniotic fluid. Isolation of virus or PCR
2) IgM antibodies in fetal blood
What are the characteristics of Picornaviruses?
Pico + RNA + viruses = small RNA virusess

Diameter 20-30 nm
Naked Icosahedron
s.s. RNA (+) - Class IV

Replication in cell cytoplasm
What are the Enteroviruses, and what is this a sub-family of?
Enteroviruses are a subfamily of Picornaviruses

1) Polioviruses types 1-3
2) Coxsackie A viruses types 1-24
3) Coxsackie B viruses types 1-6
4) Echoviruses types 1-34
5) Enteroviruses types 68-72
What are the epidemiological and pathogenesis characteristics of Enteroviruses?
One strain can cause different symptoms, and different strains can cause identical symptoms

Most infections are asymptomatic

Fecal-oral transmission

Wide spreading in poor sanitary conditions and crowding

***Highly prevalent viruses
In nature - Human entero viruses infect only humans

Incubation period of 1-3 weeks. Very stable viruses.

***Most severe disease occurs in infants and adults.
What is poliomyetlitis? What are the characteristics?
Infection of Polio in the neurons.

Viral spread either via blood stream or along axons (inefficient)

Neurons are the target organ, and virus causes destruction of the cells.

Incubation period average of 6-20 days, with a range of 3-35 days
What are the possible outcomes of infection by poliovirus?
1) Inapparent infection - 90-95%. Virus can be isolated from stool or throat swab

2) Abortive disease - 4-8%. Mild, febrile disease, flu like

3) Non paralytic poliomyelitis - 1-2%. Mild disease associated with viral invasion of the CNS - aseptic meningitis

4) Paralytic poliomyelitis - 1-2%. Paralysis associated disease. Paralysis is the result of neurons destruction. Inflammatory reaction around the nerve may also affect its function. Motor never damage is PERMANENT
What are the clinical symptoms of Poliomyelitis Paralytic disease?
1) Meningeal irritations
2) Asymmetric paralysis
3) Damage mainly to spinal cord nerve
4) In severe cases - invasion of the brain
5) Viral replication in nerve cells results in permanent destruction

***Adults and infants are severely affected. Children - mostly asymptomatic
What is the epidemiologic paradox of polio?
Improvement of sanitary conditions and hygienic levels brigns about a more severe form of the disease and large epidemics.

Reason: Infection at an older age and large non-immune populations (no previous exposure to develop Ab)

***Massive vaccination changes this phenomenon
What is the epidemiology of Polio?
Worldwide prevalence - in tropical areas all year, in moderate climate in the summer and fall.

**In nature, infects only humans

**Before the vaccination era:
1) Children are more susceptible. Adults have acquired immunity
2) In isolated areas (arctic zone) the population at all ages is susceptible - outbreaks
3) In developing countries infection at early childhood
What are the protective antibodies against polio?
Serum antibodies against each of the types (1, 2, 3)

Intestinal IgA antibodies provide protection at the port of entry

**The virus infects only man - it is possible to achieve global eradication with proper use of vaccination
What are the different polio vaccines?
IPV - Inactivated Polio Vaccine - inactivated vaccine - Salk
OPV - Oral Polio Vaccine - attenuated (mutants) vaccine - Sabin
What diseases are associated with Non-Polio enteroviruses?
Non-polio paralysis
Aseptic meningitis/encephalitis
Carditis
Rash
Acute hemorrhagic conjuctivitis
Upper respiratory illness
Neonatal infection
What type of virus is Polio?
Enterovirus
How is the laboratory diagnosis of Polio made?
1) Isolation of the virus, mainly from stool, in cell cultures.

2) Increase in the titer of neutralizing antibodies to the specific strain involved in the disease (1, 2, 3)
How is the laboratory diagnosis of Non-Polio Enteroviruses made?
1) Isolation of virus from stool
~Not necessary diagnostic
2) Isolation of virus from CSF, pericardial fluid etc.
~Diagnostic

***No good serological diagnosis
What are the three major causes of viral gastroenteritis?
Rotavirus
Enteric Adenoviruses
Norwalk virus
What is the presentation of viral gastroenteritis?
A limited disease - combination of diarrhea, nausea, vomiting, low grade fever, abdominal pains.

May be endemic or epidemic
What are the characteristics of Rotavirus?
d.s. RNA
Icosahedron
No Envelope
Several strains in man and animals
What are the epidemiology, clinical symptoms, and diagnosis of Rotavirus?
Epidemiology - Causes diarrhea mainly in infats and elderly people. In other age groups, the infection is a symptomatic

Clinical symptoms - Mild diarrhea to severe disease. Typical symptoms - vomiting

Diagnosis - Identification of the virus in stool by EM. Identification of antigen in stool by EIA
What are are the characteristics, epidemiology, and diagnosis of enteric adenoviruses?
Specific serological groups of adenoviruses 40 and 41.

Do not replicate in cell cultures.

Epidemiology and clinical features similar to Rotaviruses

Diagnosis - Identification of specific antigens in stool by ELISA
What are are the characteristics, epidemiology, and diagnosis of Norwalk like virus - noroviruses?
s.s. RNA (+) - Caliciviridae family
Non-enveloped
Icosahedron

Causes diarrhea in children and adults.

Outbreaks occur from contaminated food.

Repeat symptomatic episodes despite the presence of antibodies.

**Do not play an important role in infant gastroenteritis
What are the characteristics of HFVs?
All RNA viruses
All have Envelop
All have animal or insect reservoir in which they co-exist

Geographically restricted to their reservoir's natural habitat

Humans not natural reservoir but are infected via contact with the HFV hosts
How are HFVs transmitted?
Exposure to urine, fecal matter, saliva, or other body excretions from infected reservoir hosts or vectors
What HFVs are capable of human to human vector transmission?
Ebola, Marburg, Lassa and Crimean-Congo hemorrhagic fever
What are the shared clinical symptoms of HFVs?
Vascular system damage
Large hemorrhages from teh surface epithelium of the body, including mucous membranes
What is the pathogenesis of HFVs?
Pathogenesis not entirely clear
~Thrombocytopenia, leukopenia
~Strong hemorrhage - cause unclear
~Hypovolemic shock and death within hours - cannot be explained only by blood loss
~Liver necrotic damage
~In some cases: disseminated intravascular coagulation (CID)
What HFV presents with Maculopapulr rash?
Marburg disease
What is the vector for Lassa Hemorrhagic Fever, and where is it geographically distributed? What family is it part of?
Rodent, West Africa, Arenaviridae
What is the vector for Ebola, and where is it geographically distributed? What family is it part of?
Unknown, Africa, Filoviridae
What is the vector for Marburg, and where is it geographically distributed? What family is it part of?
Unknown, Africa, Filoviridae
What is the vector for New World Arenaviridae, and where is it geographically distributed? What family is it part of?
Rodents, Americas, Arenaviridae
What is the vector for Crimean-Congo Hemorrhagic Fever, and where is it geographically distributed? What family is it part of?
Tick
Africa, Central Asia, Eastern Europe, Middle East
Bunyaviridae
What is the vector for Rift Valley Fever, and where is it geographically distributed? What family is it part of?
Mosquito
Africa, Saudi Arabia, Yemen
Bunyaviridae
What is the vector for Hemorrhagic Fever with Renal Syndrome, and where is it geographically distributed? What family is it part of?
Rodent
Asia Balkans, Europe, Eurasia
Bunyaviridae
What are the HFVs of Bunyaviridae?
Crimean-Congo Hemorrhagic Fever
Rift Valley Fever
Hemorrhagic Fever with Renal Syndrome
What are the HFVs of Filoviridae?
Ebola, Marburg
What are the HFVs of Arenaviridae?
Lassa Hemorrhagic Fever, New World Arenaviridae
What are the diseases of Flaviviridae? What are their vectors and geographic locations?
Dengue Fever, Dengue hemorrhagic fever, Dengue shock syndrome
Vector - mosquito
Asia, Africa, Pacific, Americas

Yellow Fever
Vector - mosquito
Africa, Tropical Americas

Omsk Hemorrhagic Fever
Vector - Tick
Central Asia

Kyasnur Forrest Disease
Vector - Tick
India
What family do Hantaviruses belong to?
Bunyaviridae
What are the characteristics of Hantaviruses?
Small, s.s. RNA (-)
Genomic RNA is in 3 segments
Helical morphology
Enveloped

Replication occurs in cytoplasm

Rodents are natural hosts, but virus can transmit to humans. Rodents are asymptomatic, and each virus subtype specific to different rodent family
How and where was Hemorrhagic fever with Renal Syndrome identified?
In Korean war, thousands of soldiers got sick.

In 1978 the responsible virus was isolated from a field mouse in Korea, and called hantaan virus
What is the clinical progression of Hemorrhagic fever with renal syndrome?
A febrile phase of 3-7 days, followed by hypotensive phase (hrs to days) with hemorrhage, thrombocytopenia.

1/3 of the deaths occur from hypovolemic shock at this stage.

With return of BP to normal, 3-7 days oliguria phase: 1/2 deaths occur at this phase.

Then recovery, diuresis phase.

Major pathological lesions in fatal cases: disseminated hemorrhages and microscopic abnormalities in the kidneys
What are the characteristics of Lassa Fever Virus?
s.s. RNA (-)
Enveloped
Replication in cytoplasm

Part of Arenavirus family.

Infects specific rodents in West Africa. Endemic infection from rodent to human in rural areas in West Africa. Million of people have antibodies.

Most infections are asymptomatic. 20% have clinical symptoms with 5-15% mortality rate.

Social changes and population migrations caused large eruptions of the disease

***The disease can be transmitted from human to human. Nosocomial infections are very dangerous
How is Lassa Fever spread?
Endemic mice in West Africa can spread the disease to the local population

***The disease can be transmitted from human to human. Nosocomial infections are very dangerous
What is the clinical progression of Lassa Fever?
Infection by virus in rodent urine - by exposure to skin or aerosols

Incubation period of 1-2 weeks

Pantropic viruses - following viremia, several organs are infected - focal necrosis in the liver, pneumonia, heart and kidney damage, facial edema, encephalopathy. Hemorrhages in 1/3 of patients.

Sudden death from hypovolemic shock

Pathophysiology of the hemorrhagic disease and the shock syndrome are not understood
What is the possible treatment for Lassa Fever?
Ribavirin may be effective if given early
What are the characteristics of Filoviruses?
Long filaments, string like viruses
Sometimes wrapped around, or U-turns.
s.s. RNA (-)
Helical nucleocapsid
Enveloped

They can be propogated in vero cells in tissue culture (cells from African green monkeys)

They can infect Guinea pigs, Hamsters, and Monkeys
What are the two important HFVs of the Filovirus family?
Ebola virus - three subtypes
Marburg virus - one subtype

No antigenic cross-reactivity
What is the natural reservoir for Marburg Virus?
Unknown what the natural reservoir is

Discovered by infected monkeys imported from Uganda. Killed 31 lab workers. Checking indigenous monkeys in Uganda, no sera antibodies were found. Thus, not the natural host.
What are the major subtypes from the 1976 outbreaks of Ebola?
Ebola-Zaire - Aggressive, 88% mortality rate
Ebola-Sudan - 53% mortality rate

**Most infections are asymptomatic
How does the Ebola virus spread?
By close contact with patients.

***Many nosocomial infections resulting from contaminated syringes that were not sterilized properly

Both epidemics ended after institution of quarantine procedure, and correct sterilization protocols
What is Ebola-r
Ebola-Reston

Name for a virus identified in 1989-1990 that infected monkeys shipped from Phillipines to US. Virus was a Filovirus.

Ebola-r infects humans but does not cause disease.

Natural reservoir not known, but probably not monkeys
What is the clinical progression of Ebola?
Incubation period of 2-19 days

First, non-specific symptoms. Fever, headaches, stomach aches, muscle pains

In 2-3 days, deterioration, nausea, vomiting. Later, rash, hemorrhages in skin and mucous membrane and in internal organs. The reason for the hemorrhages is not known. It is accompanied by thrombocytopenia and thrombocyte aggregation.

6-9 days from appearance of disease - strong decreased in BP and death from hypovolemic shock. Not entirely explained by blood loss.

***Of all hemorrhagic disease, filovirus diseases have the highest mortality rates, the worst hemorrhages, and most liver necrosis
What are the worst hemorrhagic disease?
Filoviruses

Highest mortality rate
Worst Hemorrhages
Most liver necrosis
What is the epidemiology of Filoviruses?
Some infections of monkeys in nature and transmission from monkeys to humans

In large outbreaks of Marburg and Ebola, most of the infections were caused by contact with secretions

Nosocomial infections were an important factor in the virus spread

The natural reservoir has not been identified. It may be possible that some amplification is carried out in monkeys and transmitted from them to humans
How is the diagnosis of Filoviruses made?
Isolation of virus in Vero cells in tissue culture

Direct identification of virus particle sin secretions by EM

Identification of viral antigens or nucleic acids in tissues or in cell cultures

***Because of danger to lab workers, the analysis of suspected materials should be carried out in high-security labs (level 4)
What are the characteristics of Flaviviruses?
s.s. RNA (+)
Enveloped
Replicate in cytoplasm
Budding through intracytoplasmic membranes (ER)
Flavus = yellow, yellow fever

Infection vectors of mosquito or tick (usually). Vector is asymptomatic (usually)
What family does Dengue belong to?
Flaviviridae
Has 4 antigenic types
What is the most important mosquito vector for dengue?
Aedes aegypti - the virus replicates in mosquito cells.

There is also a natural reservoir for the virus in monkeys in Africa and South East Asia
How does Dengue transmit from human to human?
Mosquito must bit infected human during viremia to transmit to another human
What was the change in epidemiology following 1950 for Dengue?
After second WW, migraiton and urbanization created unfit living conditions, which were good conditions for the Aedes mosquito.

Rapid spread of the virus in dense populations
Where are endemic areas of Dengue? What factors contribute to large outbreaks?
Caribbean, South America, Pacific Ocean, China, Southeast Asia, Africa, mostly tropical areas.

Appearance of Aedes Aegypti and resistance to insecticides contributes to outbreaks.

Today, virus i endemic in 100 countries and endangers 2.5 billion people
How is Dengue life threatening?
Since the 1950s, appearance of new syndrome of Dengue Hemorrhagic Fever accompanied by Dengue Shock Syndrome - high mortality rate
What is thought to cause the more severe form of Dengue disease?
Dengue Hemorrhagic Fever accompanied by Dengue Shock Syndrome - high mortality rate

Because of higher mobility of people, co-appearance of more then one Dengue strain in same region. Infection with more then one strain thought to cause disease
What is the general trend in DHF cases in Thailand, Indonesia, and Vietnam?
Dramatic increase of cases to the present, contributed to by spread of vector.
What are the clinical signs of Dengue?
Incubation period from 2-7 days

Severe muscle and bone pains, anorexia, nausea, vomiting, extreme weakness

In some cases: dengue hemorrhagic fever with bad hemorrhages all over

Death from hypovolemic shock
Where is DHF localized to?
Africa, Southeast Asia, Americas

Every year 100 million people have disease by Dengue, and 250,000 have DHF
How is Dengue diagnosed and treated?
Diagnosis - Virus isolation or serological tests

Treatment - Supportive therapy can reduce mortality from 15% to less than 1%
How can Dengue be prevented?
No vaccine

Drying water reservoirs to limit mosquito spread

Mosquito extermination by insecticides

Aedes mosquitoes are found in areas with no Dengue. If they bite a viremic traveler, Dengue will appear in that region.

Also risk of transfer of infected Aedes on planes.
What is the West Nile Virus?
A Flavivirus
What is the clinical presentation of WNV?
Incubation period of 1-6 days
Fever, head, back, and muscle aches, anorexia
In half the cases - rash on chest, back, extremities
The disease lasts 3-6 days
In a small percentage of cases - aseptic meningitis or meningoencephalitis. Mostly in older peoplel
How is WNV diagnosed?
Virus can be isolated from the blood of 38% of infected patients.

Serological diagnosis - problems of cross-reactivity with other flaviviruses
What is the epidemiology of WNV?
Present in Africa, Middle-East, part of Europe, India, Indonesia. In recent years, USA too.

The Nile area is hyperendemic to the virus. In Cairo, 70% of people over 4 have antibodies.

Vector is mosquito - Culex univittatius, Culex pipiens molestus

Virus isolated from wild birds in many areas. Birds in Egyps, South Africa and Israel have high virus titers
What is the WNV human infection "iceberg"?
~80% asymptomatic
~20% "West Nile Fever"
~<1% CNS disease
~<0.1% Fatal
What is the clinical description of WNV?
Most WNV infections are mild or unapparent

~80% asymptomatic

About 20% develop West Nile Fever
~sudden onset of mild febrile illness
~often accompanied by: malaise, anorexia, nausea, vomiting, eye pain, headache, myalgia, rash and lymphadenopathy
~Symptoms are normally self-limiting and last 3 to 6 days

Less then 1% of infections cause severe neurological disease

Most significant risk factor for severe neurological disease is advanced age

Case fatality rate is estimate at 10% of those with severe neurological symptoms, or roughly <0.1% of total infections
What were the WNV infections in 2002 in the USA?
Human:
~4156 infections
~284 deaths (median age 77, range 19-99. Gender 64% male)

Avian:
~16,739

Veterinary:
~>14,571
~1 cat, 7 dogs, 24 other species, remainder equine
How is WNV prevented and controlled?
No vaccine.

In time of outbreaks, exterminate mosquitoes