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168 Cards in this Set
- Front
- Back
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Virion
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The virus particle:
Made up of: 1. Viral nucleic acid 2. viral structural proteins 1+2 = nucleocapsid |
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Properties of viruses
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Small, infectious, obligate intracellular parasite
Genome- DNA or RNA In host cell, genome is replicated and directs synthesis of other virion components by host systems De novo assembly of of progeny virions |
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Viral structural proteins
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Encoded by viral genome (not host)
Packaged into virion- provides protective coat to nucleic acid Includes: capsid (protein) and lipoprotein envelope (some viruses: viral protein + cell membrane) |
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Nonstructural proteins
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Encoded by viral genome
Not packaged into virion Usually enzymes or transcription factors Necessary for viral replication in cell (first segment in ssRNAsense) |
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Classification
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RNA or DNA
Symmetry of capsid Presence/absence of envelope Dimensions of virion & caspid Genome: RNA: ss: Plus strand RNA: ss: Minus strand: nonsegmented v. segmented RNA: ds: segmented DNA: ss DNA: ds: linear or ciruclar |
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Virus Evolution
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RNAP lack proofreading fxn
Population = quasispecies Can evolve by: Mutation Recombination (two viruses) Reassortment (2 viruses w/ segmented genomes) Ex: human + swine + avian reassortment in host |
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Growth
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One step growth curves for viruses compared to bacteria
Takes longer to replicate, but viral load gets many folds higher than bacteria |
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Cell surface molecules for virus attachment
and Binding sites on viruses |
Carbohydrates- sialic acid, glycosaminoglycans
Lipids- glycolipids, proteolipids Proteins- Ig superfamily, complement regulatory proteins, integrins, TNF receptor superfamily Receptor binding sites on viruses -Depressions (Picornavirus) OR -Projections (Rotavirus) |
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Where RNA and DNA genomes make mRNA...
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RNA viruses- CYTOPLASM
(exception: Influenza!) DNA viruses- NUCLEUS |
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How to get a lot of information into a small genome
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-Overlapping reading frames
-Coding off both strands -RNA splicing -Frame-shifting -RNA editing |
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How to persist in population
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-Do NOT kill host
-Do NOT kill cells in which virus is replicating -Do NOT get eliminated by immune response |
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How to have sufficient stability for transmission, but sufficient instability for cell infection
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Endocytosis
-enveloped & nonenveloped -clathrin-coated pits -Entry into sytoplasm, then fuses w/ endosomes w/ acidiphication -acidiphication necessary for viral protein conformational changes (like HA of influenza) Fusion -Enveloped virus fuses directly w/ cell membrane -Virus discharged into cytoplasm |
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Interferons
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Viral ds RNA infects cell
Interferon synthesis and liberation Protein induced blocks replication of unrelated virus IFN binds to IFN receptors, signal through JAK-STAT pathway to induce antiviral protein genes IFN control spread of virus prior to appearance of acquired immune response |
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Antiviral antibodies (tests)
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Serological tests- used for dx
-Enzyme immunoassays -RIA -W. blot Biological activity- gives info on fxn of Ab -Virus neutralization -Complement fixation -Hemagglutination inhibition (viruses bound together, can't infect) |
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Cell-mediated immunity in viral infection
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Focus immune response to cells expressing MHC I
Clear infected cells Recruit other effector cells Activate macrophages Provide help for production of antibody by B cells |
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Human picornavirus
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Plus-strand RNA viruses
Small Rhinoviruses Enteroviruses (Polioviruses, ECHO viruses, ENteroviruses, Coxsackie) Hepatitis A virus RNA replication in cytoplasm 3 surface proteins, 1 interior protein Receptor binds into "canyon" of picornavirus Plus strand RNA is translated into a single polyprotein Virus-encoded proteases process polyprotein into individual proteins Internal ribosomal entry site (IRES) in 5' nontranslated region of RNA IRES allows NA to bind directly to ribosome w/o need for 5'7-methyl G cap Rhinovirus: local URIs (problems in asthma pts) Enterovirus: cause systemic infection (general viremia-> other organs) Rash from enterovirus infection Poliovirus: replication in motor neurons in spinal card Poliomyelitis: inflammation and death of motor neurons Virus encoded protease 2A cleaves EIF4G that binds cap-binding protein to assemble initiation complex (shuts off host cell protein synthesis) |
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Polio
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Human picornavirus
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Viral Virulence
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Under polygenic control
Virulent- causes disease Attenuated- no or reduced disease Avirulent- no disease Virulence genes: Affect ability of virus to replicate Defeat host's defense mech Promote virus spread w/in and among hosts Gene products that are toxic- cause cell injury directly |
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Viral Tropism
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Virus has to enter cell- susceptibility
Virus has to replicate in cell - permissivity Neurotropism Pneumotropism Enterotropism etc ALL= PANTROPISM |
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Viral Receptors
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Required for virus entry
Determines host and tissue tropism Some viruses need co-receptor Active process Integrins Ig-like molecules GLycosaminoglycans CHO |
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Viral Spread
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Local replication
Systemic spread- must cross barriers such as basement membrane Directional release- major determinant of infection pattern (influenza virus into lumen) (vesicular stomatitis virus crosses basement membrane) |
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Viremia
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Circulating virus in blood (in circulating WBCs)
DISSEMINATION Monocytes- Measles, HIV, CMV Lymphocytes- HIV, Epstein-Barr, Human herpesviruses 6&7 Neutrophils- Influenza virus Free- Poliovirus, HepB |
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Viruses vs. Respiratory System
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Transmission: hand-shaking, coughing, sneezing
Host Defense: Mucociliary apparatus, Alveolar macrophages, Adaptive immune response URI: Rhino, Influenza Lower: Adeno, Influenza |
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Viruses vs. GI Tract
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Transmission: eating, Drinking, poor hygiene
Host Defenses: Stomach pH, digestive enzymes, flow of ingesta, Adaptive immune response Rotavirus Reovirus (translocated across M cell) Measles Poliovirus Adeno |
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Viruses vs. UG Tract
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Transmission: Sexual activity, fecal contamination
Host Defenses: Urine flow, thick epithelial layer, acid pH, Adaptive immune response HIV, HSV (lifelong persistent or latent infections) HPV- associated w/ cervical cancer |
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Viruses vs. Eyes
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Transmission: COnjunctiva, abrasions, direct inoculation
Host Defenses: Tears, thick epithelia layer, Adaptive immune response HSV: lifelong persistent or latent |
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Viruses vs. Skin
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Transmission: cuts, abrasions; insect bites; needles
Host Defenses: epidermis, skin oils Poxviruses Papillomaviruses Rabies Togaviruses- insects Alphaviruses- insects Measles virus, chicken pox- come up to skin and replicate |
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Viruses vs. Nervous System
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Transmission: cuts, animal bites; inhalation; cell trafficking
Host Defenses: Blood-brain barrier Rabies HSV HIV Measles Alphaviruses Enter via sensory nerve ending and move retrogradely Can be latent in DRGs (good example is HSV) |
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Cytopathic Effects
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Cell swelling
Necrosis Apoptosis Inclusion bodies Syncytia/multinucleated giant cells Cellular hyperplasia/proliferation |
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Cytopathic Effect: Viral Inclusions
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Inclusion Bodies
Viral Inclusions: viral and/or cellular products, present very early in infection, intranuclear and/or intracytoplasmic, Eosinophilic, basophilic, amphophilic Peripheralization of chromatin Only aid in diagnosis Herpesvirus- eosinophiic intranuclear inclusions CMV- Owl's eye inclusion |
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Cytopathic Effect: Necrosis
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Necrosis
shutdown of protein, nucleic acid synthesis; accumulation of viral components in cell Ballooning degeneration Cell death- pyknosis (chromatin clumping); hypereosinophilic cytoplasm Disruption of tissue architecture Fetal dev- malformations |
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Cytopathic Effect: Apoptosis
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Promoting Apoptosis: initiation/promotion of cascade
Aids in virus dissemination (lysis) Inhibiting Apoptosis: permits longterm virus replication, establishes latency |
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Cytopathic Effects: Syncytia
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Viral fusion proteins expressed on surface of cells cause cells to fuse together, producing multinucleated cells
Seen in vivo or in vitro Purpose: permits virus transmission w/o exposure to host defenses |
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Cytopathic Effects: Hyperplasia/proliferation
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Usually self-limited, transient
May be due to atypical differentiation, accumulation of viral products May be pre-neoplastic Ex: Molluscum contagiosum (pox virus) |
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Virus-induced neoplasia
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Often involves integration of viral genomes into host DNA
Ex: Epstein-Barr virus- NP carcinoma - Burkitts Lymphoma HPV- cervical carcinoma HTLV-2- T-cell leukemia |
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Classic host inflammatory response to viruses
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Mononuclear cells:
Lymphocytes Macrophages |
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Host susceptibility to viral disease
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Genetic determinants:
Diversity of MHC Class I genes Specific resistance genes Non-genetic determinants: Age-related reduced immune competence: infants, elderly Gender- males, pregnant women Malnutrition Corticosteroids, cigarette smoking, stress |
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Cytopathic Effects: Syncytia
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Viral fusion proteins expressed on surface of cells cause cells to fuse together, producing multinucleated cells
Seen in vivo or in vitro Purpose: permits virus transmission w/o exposure to host defenses |
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Cytopathic Effects: Hyperplasia/proliferation
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Usually self-limited, transient
May be due to atypical differentiation, accumulation of viral products May be pre-neoplastic Ex: Molluscum contagiosum (pox virus) |
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Virus-induced neoplasia
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Often involves integration of viral genomes into host DNA
Ex: Epstein-Barr virus- NP carcinoma - Burkitts Lymphoma HPV- cervical carcinoma HTLV-2- T-cell leukemia |
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Classic host inflammatory response to viruses
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Mononuclear cells:
Lymphocytes Macrophages |
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Host susceptibility to viral disease
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Genetic determinants:
Diversity of MHC Class I genes Specific resistance genes Non-genetic determinants: Age-related reduced immune competence: infants, elderly Gender- males, pregnant women Malnutrition Corticosteroids, cigarette smoking, stress |
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Key differences between positive and negative strand viruses
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Positive Strand RNA Virus:
-First replication step: polymerase synthesis via genomic RNA translation - strand has non-structural proteins-structural proteins (Polarity) -Must translate RNAP Negative Strand RNA Virus -First replication step is + strand RNA synthesis (mRNA, full length antigenome) -strand is structural proteins-non-structural proteins (Polarity) -RNAP is component of incoming virion |
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Negative strand viruses: Key Features
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RNA is not infectious!
Virion contains RNA dependent RNA polymerase Genomic RNA is packaged in protein (encapsidation) -Structure = nucleocapsid Nucleocapsids have helical structure Virions are enveloped Entry by virion fusion or cell-cell fusion Important** Influenza A,B,C Parainfluenza 1-4 Mumps Measles Respiratory Syncytial Rabies |
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Influenza Viruses
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3 types A, B, C
A & B antigenically distinct, structurally similar Influenza A- infects ducks, chx, horses, swine Influenza virus- avian strains rarely infect humans |
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Influenza Virion
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Structural features:
HA, NA, M2 Genome comprised of segments; 1-3 genes/segment; HA and txn complex on separate segments Lipid envelope contains viral glycoproteins (HA, NA) |
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Gene Reassortment
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2 different strains infect same cell
Replication of all genome segments Virus assembly with mixing of segments End Result: Reassortment Progeny Viruses |
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Reassortment causes Antigenic SHIFT
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For example:
The new virus can replicate in human cells Humans lack immunity |
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Influenza virus Hemagglutinin
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16 antigenic types
Trimer; globular head on stalk Multifunctional -Binds cellular receptor sialic acid -Binds and agglutinates rbc's -Mediates fusion of viral envelope w/ cell membrane HA synthesized in "pro-form" -Cleavage required for conformational change/activation of fusion function -Cleavage by tryptase Clara (serine protease secreted by nonciliated Clara cells in bronchial and bronchiolar epithelium found in lumen of respiratory tract) Target of neutralizing antibodies -Minor mutations result in antigenic DRIFT Replacement with gene from alternate hosts results in antigenic SHIFT |
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Influenza virus entry into host cell
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Binding
Virus particle endocytosed Low pH-induced HA conformational change w/in endosome -Exposure of hydrophobic aa's in HA (mels w/ membrane) Fusion of viral envelope w/ endosome membrane Release of genomes into cytoplasm No syncytium formation |
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Influenza virus Neuraminidase
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Tetramer
Function: during virus exit, cleaves sialic acid residues on cell surface Influenza A: 0 recognized subtypes **If mutant neuraminidase gene, virus cannot cleave and disperse |
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Influenza nomenclature
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Type/location/ # of isolate/ year of first isolation/ HA and NA subtypes
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Influenza virus M2 Protein
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Tetramer
Spans viral envelope Function: Pumps protons into virion at low pH Loosens protein-protein contact Facilitates virus uncoating Target for amantadine |
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Influenza virus replication
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Genome replication occurs in nucleus
-virus lacks mRNA capping and methylating enzymes -steals caps from host mRNAs -cap plus 10-13nt are used to prime viral mRNA synthesis Viral mRNAs are translated on SER and RER -HA and NA transported thru Golgi to cell membrane Virus replicates in ciliated columnar epithelial cells in respiratory tract -causes tracheobronchitis Lg numbers of virions shed into resp tract- facilitates transmission Virus-induced apoptosis of infected cells Infection damages resp tract -PROTECTIVE MUCUS LAYER DISRUPTED -Resp epithelium denuded |
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Influenza Virus Clinical features
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Transmission
-Resp -Seasonal, primarily winter Symptoms -Appear 1-4d post infection -HA, fever, myalgias, nonprod cough, sore throat, no rhinorrhea -Lasts 3-7 d -Likely caused by local prod of interferon and IL-1 (immune response) |
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Influenza Immunity
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Innate:
Mucus barrier Clearance by cilia Alveolar macrophages Adaptive Protection: IgA (mucosal); IgG (serum) Clearance: IgG + complement; CTL At risk: Elderly, smokers, chronic pulm disease (emphysema) *Mucus barrier disruped |
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Influenza virus complications
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Primary virus infection
-Interstitial pneumonitis Secondary bacterial pneumonia -Facilitated by damage to innate immune system -Destruction of ciliated epi cells -Abnormal macrophage function Secondary- repsonds to Abx, mortality lower than primary Primary viral pneumo common in pregnancy-> pregnant women should definitely get vaccinated! |
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Influenza Immunization
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KILLED (inactivated) vaccine (primarily HA, NA)
-Reformulated every year -Recommended for health care workers, at risk pop -Provides partial protection LIVE ATTENUATED INTRANASAL VACCINE (FLU MIST) Replication restricted to nasopharynx Cold adapted Reformulated annually Approved for use in healthy people 2-65 yrs |
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Influenza Dx
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Direct detection- staining of NP aspirates w/ flu-specific monoclonal antibodies
Culture |
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Paramyxoviruses
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8 medically important viruses
Parainfluenza 1-4 Respiratory Syncytial Virus (Pneumovirus) Human Metapneumovirus Measles (Morbillivirus) Mumps (Rubulavirus) Characteristics: Do NOT undergo epidem. important antigenic change NO natural reservoir- cont. person-person spread Spread by resp route Proteins: H (glycoprotein) mediates receptor binding F (glycoprotein) mediates fusion Nonsegmented genome mRNAs generated by polymerase reinitiation Glycoproteins- carbs attached in ER, Golgi Cell attachment protein- H Fusion protein- F (to be active must be cleaved into F1, F2 by intracellular proteases at neutral pH) Replication cycle: Virions fuse at cell membrane RNAs synthesized in cytoplasm H/F transported thru ER/Golgi to plasma mem Nucleocapsids assemble Budding from cell membrane OR fusion w/ adjacent cell (fusogenic surface proteins at neutral pH) |
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Resp Syncytial Virus
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Causes outbreaks of resp disease in winter
Direct contact w/ resp secretion Causes otitis media, bronchitis, bronchiolithis, croup (infection of larynx&trachea), pneumonia Most severe in young infant Partial immunity post primary infection Primary RSV URI can progress in severity -cough, weezing -dyspnea, increased RR, hypoxemia Dx: direct staining of NPAs w/ fluorescent monoclonal antibodies, culture Vaccine: under dev. |
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Human Metapneumovirus
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Most infections occur in childhood
Serologic evidence of circ for at least 50 yrs Causes 7-40% peds resp inf. Dx: RT-PCR Antibodies for direct detection of viral antigens now available Parallels RSV: seasonal (winter); initial exposure in childhood Clinical: range from ild resp symptoms to severe cough, bronchiolitis, pneumonia Repeated infections occur- prod less severe disease limited to upper resp tract |
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Parainfluenza Diseases/Prevention
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Parainfluenza 1-3
Common cause of URIs Most common of laryngotracheo-bronchitis croup in young chidren Most children infected by 5 Dx: culutre vaccine: not yet available |
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Measles
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Geo: worldwide
Epidemics in vaccinated countries Endemics in unvaccinated Routes of transmission -resp -aerosol High attack rate High mortality rate in infants in developing countries Systemic replication -first site- resp epithelium -second site- local lymph nodes -dissemination by infected monocytes departing resp LNs (primary viremia) -Epithelial/endothelial cells infected throughout body release virus into blood (secondary viremia) Clinical Sx: Arise during secondary viremia Prodrome: fever, cough, coyza, conjunctivitis, Koplik spots Rash arises w/ immune response (cellular response) Immune responses -CD4 help -CD8 clearance -IgM, neutralizing IgG Measles-Induced immune deficiency -Gen. immunosuppression Early-lymphopenia Middle- decreased DTH responses dec lymphoproliferation Late- effects on thymus? Dx:clinical pic, direct stain, culture, serology Live attenuated vaccine: given to infants 12-15 mo |
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Mumps
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Infection of glandular epithelial cells
-Parotitis, orchitis -Pancreatitis, ovarian infection infrequent -Meningitis Dx: culture (saliva, urine, CSF) Prev: live attenuated vaccine |
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Rhabdovirus
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Rabies is only important human pathogen
Transmitted in saliva from bite of infected animal Limited replication in muscle and subepithelial tissue Uptake by sensory/motor neurons Retrograde transport to cell body (major site of replication) Early avoidance of imune response thru transynaptic transmission Symptoms: Prodrome: fever, malaise, paresthesias at bite site Later: anxiety, aggressive behavior, seizures, hypertonia, paralysis Post-exposure prophylaxis can save! Dx: clinical (exposure) history, biopsy, PCR Prev: Inactivated vaccien -Long incubation period allows for post-exposure use -Pre-exposre immunization in vocations w/ high risk (vets, wildlife mgrs) |
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Parvoviruses
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small DNA animal viruses
Icosahedral symmetry, nonenveloped 3 protein and linear ss DNA Only replicate in DIVIDING cells or cells infected w/ helper viruses Autonomous parvoviruses replicate alone Dependoviruses require a helper virus |
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Parvovirus B19
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Autonomous parvovirus
Causes childhood rash disease erythema infectiosum (fifth disease), acute recurrent arthritis, aplastic crisis in persons w/ chronic hemolytic anemia, persistent infection w/ chronic anemia in immunocomp indiv, and hydrops fetalis Replicates preferentially in erythroid precursor cells Normal child/adult: B19 infection is biphasic- viremic (fever, malaise, myalgias); erythematous RASH on face. Adult often develop arthritis Acute infection- destruction of erythroid precursors in bone marrow Transient anemia important in individuals w/ chronic hemolytic anemia due to dzs such as sickle cell, thalassemia, heriditary spherocytosis Avg. life of circulating erythrocytes is shortened (apoptosis from NSP) **Aplastic cris Immunodeficient individuals are unable to clear infection; develop chronic anemia due to RED CELL APLASIA Fetus- severe anemia-> hydrops fetalis B19 is ubiquitous, highly contagious Respiratory secretion, common in school age children & their parents No vaccien |
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Bocavirus
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Parvovirus
Infects respiratory tract |
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Adeno-associated virus (AAV)
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Dependovirus parvovirus
Causes no recognized disease Integrates into cellular DNA Being developed as vector for gene therapy |
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Papillomaviruses
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HpVs
icosahedral Supercoiled circular dsDNA Cause of warts, squamous carcinomas Replication in nucleus of squamous epithelia cellsf Viral genes expressed in 2 phases: Early (E) genes encode reg. proteins for replication, txn, transformation E2, E6, E7 important in disease Long control region (LCR)- origin of rep and control elements for txn, rep Late (L) genes encode capsid structural proteins L1, L2 |
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Papillomaviruses cont'd
cutaneous type |
Cause warts
Virus enters skin through abrasion Expression of early genes leads to hyperplasia, formation of wart Late genes encoding L1 and L2 are expressed and infectious as infected cells in basal layer differentiate into keratinocytes (move to surface) |
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Papillomaviruses cont'd
mucosal types |
Infect genital, oral, respiratory mucosa
Women- proliferating cells at border of squamous and columnar epithelium of cervix infected- flat condyloma develops Virus clearance (1-2 yrs) delayed in HIV-infected Persistent infection->cytologic abnormalities on Pap smear All cervical carcinoma initiated by HPV HPV-16 and HPV-18 most oncogenic (45, 56) Oncogenicity- assoc w/ fxn of E6, E7 E7- induces DNA syn in resting cells (bind retinoblastoma tumor suppressor pRB w/ high affinity) E6 protein activates telomerase, complexes w/ p53 (w/ E6AP, E3 ubiquitin ligase)- targets p53 for ubiquitin-mediated degradation In malignant cells, viral genome is often integrated to disrupt early gene E2 that controls expression of E6, E7 Papanicolaou smear used as screening device PCR used to type Immunization w/ VLPs from L1 capsid protein protects Recommended for teenage girls Cervical carcinoma = major cause of death due to malignancy in developing countries |
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Goals of Antiretroviral therapy
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Decrease HIV replication by as much as possible for as long as possible
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Nucleoside Analog Reverse Transcriptase Inhibitors (NRTI's)
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Approved
**Zidovudine (Azizothymidine, AZT) Mech: Phosphorylated by cellular enzymes to triphosphate (AZT-TP) AZTTP is active form! Inhibits HIV-encoded RT (RNA-dependent DNA polymerase) Acts as chain terminator Reduces plasma HIV-1 RNA minimally when used alone PK: well absorbed Eliminated by glucuronidation (Phase II conjugation) Short plasma T1/2 of parent Longer T1/2 of intracellular AZT-TP (allows infrequent dosing, bid) Rapid conversion to AZT-MP (which accumulates) Slow conversion to di- and tri- Toxicity: Bone marrow suppression, mainly anemia; less commonly granulocytopenia; rare myopathy and lactic acidosis/steatosis NRTI's toxic because poor selective tox: also inhibits mitochondrial DNA polymerase!!! (toxicity stems from mt malfunction) Resistance: Requires 5+ specific amino acid changes Develops slowly (months to years) Limited cross-resistance w/ other nucleosides Tenofovir prescribed more often |
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Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTI's)
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Approved
**Nevirapine Big difference between nuc and non-nuc is that non-nuc have very different structures (as a group) Mech: Does not require intracellular activation Non-competitive inhibitor of RT Binds to enzyme at site DISTANT from active site and causes conformational change in enzyme rendering it less efficient Efficacy: Reduces plasma HIV-1 by 2-3 logs; effects are short-lived as monotherapy Selective Tox: NO effect on human DNA polymerases PK: Well absorbed Eliminated by oxidative metab (CYP450 3A4) Long plasma T1/2, allows infrequent dosing, bid, could be qd) P450 Enzyme inducer Toxicity: Rash (common); Steven Johnson Syndrome (rare) (SJS is systemic attack by immune system of epithelium, full body burn); Hepatotoxicity (rare); Drug interactions- P450 enzyme inducer Resistance: single specific aa change, confers up to 1000-fold resistance to drug; resistance emerges rapidly (days to weeks); Single point mut also confer Cross resistance to other NNRTI's |
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Efavirenz
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Selective, potent NNRTI
Long half-life qd CSF and semen HIV-RNA reduction Safe, well tolerated Pregnancy should be avoided Treatment convenient: 1 pill qd Coformulation- 3 drugs/pill |
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HIV Protease Inhibitors PI's
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Approved
Saquinavir Ritonavir Mech: Does not require intracellular activation; Competitive inhibitor; Transition state peptidomimetic inhibitor (chemical analog of transition state) *Protease cleaves pre-proteins into mature proteins Protease inhibitor --I infectious virus (non-infectious immature virus can still persist) HIV PI's do NOT prevent virion formation and release, but inhibit virion maturation Selective Tox: Do not inhibit human aspartyl proteases; Reduce plasma HIV-1 RNA by 2-3 logs as monotherapy. Partially restore CD4 cell count PK: Variable bioavailability due to first-pass metab and autoinduction Highly protein-bound Eliminated by oxidative metab (CYP450 3A4) Plasma T1/2 3-5 hours, dosed bid Potent P450 enzyme inhibitor (3A4>2D6) and hepatic enzyme inducer Toxicity: GI intolerance n/v, diarrhea; Hyperlipidemia (common w/ antiretroviral drugs) Glucose intolerance (rare) Associtaed w/ fat redistribution (more strongly associated w/ stavudine) Hepatic transaminits (rare) Circumorla and extremity parasthesias (common during first few weeks) Drug Interactions* Ritonavir enhances plasma concentrations of other protease inhibitors Resistance: An initial single aa change confers 3-5 fold resistance = PRIMARY RESISTANCE SECONDARY aa changes accumulate, conferring ever-increasing resistance (up to 100-fold) Resistance emerges w/in weeks to months (not in all subjects) Accumulated mutations confer partial or complete cross-resistance to other PI's Dose-response curve: higher doses of drugs suppress emergence of resistance genotype. |
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Integrase Inhibitors
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Approved
Raltegravir Mech: inhibits HIV integrase DNA strand-transfer rxn essential for chromosomal integration Oral drug, bid Highly potent anti-HIV effects Well tolerated, little/no tox |
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Entry Inhibitors- Enfuvirtide
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Approved
Enfuvirtide Mech: interferes w/ membrane protein helix bundle formation necessary for membrane fusion and entry (analog of piece of HIV envelope protein) Must be injected bid Expensive Reserve for highly treatment-experienced pts |
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Entry Inhibitor- Maraviroc
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Approved
Maraviroc (CCR5 antagonist) Mech: selectively inhibits HIV entry mediated by CCR5 chemokine co-receptor Only approved antiretroviral that targets host protein Oral, bid Only effective in pts w/ CCR5-trophic HIV (need phenotypic sensitivity test to prescribe) Treatment-experienced pts |
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Antiretroviral Usage Today
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Combination therapy ONLY
Potent drug combos: HAART = Highly Active Antiretroviral Therapy Most popular starting regimens: Efavirenz + 2 NRTI's Potent PI + 2 NRTI's Rational: Prevention of drug resistance (Minimum of 3 active agents required to prevent emergence of resistance) No role for synergy Reduced pill burden: Co-formulated drugs Once-daily regimens Better long-term tolerability Central role of resistance testing |
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Influenza A
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4 subtypes of flu A have circulated among humans recently:
H1N1, H1N2, H3N2, and novel (swine) H1N1 Flu viruses mutate regularly Antigenic drift: -Variations of antigens w/in same H and N class; -Requires annual reformulation of influenza vaccine Antigenic shift: -Complete change in H, N or both H and N -Occurs when bird strain re-assorts w/ human strain |
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How does Influenza cause a pandemic?
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Susceptible population (no immunity)
Transmission from animals to humans Transmission from human to human Sustained human to human transmission (avian flu did not see sustained human-human as seen w/ swine flu) |
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Influenza
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Season: annual epidemic spread; late fall, winter, early spring; most influenza occurs in Jan/Feb
Epidemiology: All ages, highest rates in children, serious illness/death >65, <2, high risk; Annually 36,000 deaths in US (most >65) Clinical signs: Abrupt onset of constitutional and resp signs/symptoms: malaise, myalgias, headache, fever, non-productive cough, rhitis, sore throat, otitis Uncomplicated dz resolves 3-7 days, cough/malaise linger up to 2 weeks novel influenza A(H1N1) affecting young age group 5-49 Complicated: primarily viral pneumo, exacerbation of underlying med dzs, secondary bac pneumo, co-infection w/ other viral/bac, **Ask about chest pain, COPD exacerbations, changes in mental status, falls... Dx: Absence of ILI does not rule out flu; lab dx and high level of suspicion during season necessary! NP Aspirate; viral culture, rapid dx tests, immunofluorescence, RT-PCR, serology |
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Influenza Transmission
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Transmission:
Person-person -large particle resp droplets Close contact Contaminated surfaces Incubation 1-4 days Adults infectious from 1 day prior to symptom onset thru 5 days after Children shed several days prior to symptom onset for more than 10 days after Immunocomp can shed for months |
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Influenza Vaccination
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Annual vaccination b/c of antigenic drift
Two types: Trivalent inactivated vaccine (TIV) -injected -grown in eggs -3 strains -inactivated, killed -subunit, subvirion, purified surface antigen -CANNOT cause influenza (killed) Live Attenuated Intranasal Vaccine (LAIV) -Intra-nasal Admin. -Grown in eggs -3 strains (same as inact) -Live, attenuated -Potential to cause mild sign and symptoms FluMist -FDA approved 2-50yrs -Should NOT be given to pregnant women, immunosuppressed pts ACIP recs -Children 6mo-19yrs -Pregnant women ->50yrs -People at or who live with/care for people at high risk for complications -Healthcare personnel H1N1 vac recs similar: pregnant, contacts/caregivers of children <6mo, healthcare workers, 6mo-24yrs, at risk of complications from flu Conditions at risk for Complications: Chronic Pulm Disease (asthma) CVD Renal, hepatic, hema-, metabolic disorders Immunosuppression Cognitive/Neuromuscular dysfunction compromising resp fxn |
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Antiviral Medications
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ADJUNCT to vacinate
4 licensed agents in US Adamantanes -Adamantadien, Rimantadine Neurominidase Inhibitors -Oseltamivir, Zanamivir Used for: Rx, Prophylaxis Adamantanes- Seasonal H1N1 susceptible, H3N2 resistant, Pandemic H1N1 resistant Oseltamivie: Seasonal H1N1 Resistant; Pandemic H1N1 susceptible |
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Polio
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Prior to vaccine:
Infection tended to be early in developing countries and late in industrialized countries. Caused paralytic poliomyelitis Jonas Salk- inactivated vaccine Albert Sabin- live virus vaccine Inactivated- currently used in US Live attenuated- generates mucosal immunity; tendency for revertants to wt When wt poliovirus was eliminated in US, all cases of paralytic polio were due to live virus vaccine Still endemic in parts of Africa, India Problems: -Importation -Circulation of recombinant viruses -Prolonged excretion by immunodeficient pts |
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Togavirus
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Enveloped icosahedral virus
Genome = mRNA for nonstructural proteins Second subgenomic RNA synthesized for translation of structural proteins *Enveloped plus-strand RNA viruses Two types: Rubella virus Alphavirus |
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Rubella Virus
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Togavirus
Enveloped plus-strand RNA virus Resp transmission, worldwide distribution Causes mild rash illness in children and adults Fetal infection->congenital rubells syndrome w/ mental retardation, heart defects, cataracts... Congenital infection: Requires maternal exposure, maternal blood invasion, placental infection, entry into baby's blood, fetal infection Highest in 1st, 3rd trimester |
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Alphavirus
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Togavirus
Enveloped plus-strand RNA virus Spread by mosquitoes, geographically restricted distribution Cause encephalitis (EEE, WEE) or rash and arthritis Encephalitis: mosquito-skin-blood-macrophages, spleen, lymph nodes- brain- encephalitis Eastern equine encephalitis Western equine encephalitis |
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Flaviviruses
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Mosquito-born viruses
-Yellow fever virus -Dengue virus -Japanes encephalitis virus -West Nile virus Tick-borne viruses Hepatitis C virus West Nile- causes encephalitis |
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Coronaviruses
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Human Coronaviruses
1. Common cold 2. Severe acute respiratory syndrome (SARS) |
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Virus properties facilitating infection of GI tract
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Resistance to low pH (stomach)
Resistance to detergents (bile) Resistance to proteases (SI) |
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Viruses that replicate in GI tract but don't cause GI disease
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Enteroviruses (Poliovirus)
Reoviruses Adenoviruses |
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Viruses that replicate in GI tract and CAUSE gastroenteritis
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**Calicivirus (Norovirus):
+ strand RNA, no envelope **Rotavirus: dsRNA, segmented, no envelope |
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Rotavirus
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Rotavirus diarrhea most common cause of severe dehydrating diarrhea in young chidren
Genome: dsRNA, purified segments aren't infectious Each segment- codes 1 protein RNA segments form diff viruses; may reassort at high freq during dual infection IN REOVIRUS FAMILY Can by typed by Electrophoresis (Electropherotypes, segment sizes) Capsid structure: Outer capsid VP4, VP7: VP7: Viral surface glycoprotein, 30% of virion VP4: 60 spikes on surface of virus, 1.5% of virion Trypsin cleavage of VP4 into VP8 and VP5 required for INFECTIVITY VP5 selectively permeabilizes membranes Contains own viral RNAP- immediately makes + strand message Histology: 1-3 days- villus atrophy and blunting, inflammation, mononuclear infiltration of lamina propia, vacuolation of epithelial cells Rotavirus infects mature absoptive enterocytes in SI **Enterotoxic nsP4 peptide Stimuation Cl- secretion by secretory crypt cells WATERY diarrhea nsP4 may also stim enteric nervous system-> Diarrhea Infects younger people Equal cause of infant diarrhea in developed, developing countries Dx: antigen-specific enzyme immunoassay More common in winter Vaccine: Two live, oral attenuated vaccines against rotavirus infection FDA approved -bovine reassortment vaccine -No clear intussusception risk Routine component of pediatric vaccine (Not in developing world) |
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Norovirus
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A calicivirus
+ strand RNA, no envelope Receptor dependent on enzyme encoded by FUT2: FUT2 encodes enzyme that produces carbohydrate H type 1 on surface of epithelia cells and in mucosal secretions to which NV attaches "secretor" status Glycosyltransferases, Lewis (FUT3) and A, B enzyme of ABO ystem can modify H type 1 sturcuture at cell surface Mutations to FUT2 or (FUT3, ABO) can render "nonsecretor" status Norovirus infection: O blood group > A or Bj Secretor status >> nonsecretor Vomiting when gastric emptying is slowed significantly No age predilection Gastroenteritis outbreaks- cruise ships, nursing homes, etc Acute Gastroenteritis - 50% of all foodborne outbreaks of gastroenteritis -Most common etiology Stool, vomit infectious Outbreaks common Many strains, little durable immunity Dx: no routine tests Rx: supportive |
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African Burkitt's Lymphoma
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Young boys
Involves maxilla, periorbital region Occurs in Equatorial Africa (not high altitude, desert) Herpesvirions seen in tumor cell culture Latent- no virions being produced Lytic- virions being produced Most Burkitt's cells are latently infected |
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Epstein-Barr Virus
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Linked to human cancer- Burkitt's
EBV immortalizes B cells Immortalized B cells: Grow indefinitely in tissue culture Tumorigenic in immunodeficient mice EBNA1 viral protein in Burkitt's cells and immortalized B cell line INVISIBLE to CD8+ T cells (immort B cells- many other proteins!) EBV latency- in Burkitt's cells; Immortalized B cells- No viral production Lytic infection- many proteins, viral DNAP, viral thymidine kinase Latent cells- genome= ds circles; require host DNAP for replication AND EBV copy nmbers not afffected by antivirals that inhibit DNAP (acyclovir) Lytic cells- ds stranded linear molecules; requires viral DNAP for replication AND Production of new virions, production of linear DNA blocked by inhibitors of DNAP |
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Diagnosis of Infectious Mononucleosis
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Sore throat
Swollen lymph nodes Lymphocytosis Heterophile antibody test~monospot test |
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EBV Infection and IM Dx
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Transmitted in saliva
95% of adults infected Infection in childhood usually asymptomatic Infection in adolescence/adulthood assoc w/ syndrome of infectious mono IM Dx: Monospot IgM to VCA IgG to VCA- indicates past EBV transmission in saliva Infects B lymphocytes In lytic infection- spread via infectious virions In latent infection- spread via cellular proliferation T and NK response- atypical lymphocytosis characteristic of mononucleosis Kills man virus infected B cells After cellular response- EBV infected resting memory B cell Virus-infected cell can reactivate and produce virus Virions infect new cells, which become T cell targets |
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Immunodeficiency and EBV
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Organ Tx Recipients
Immunosuppression w/ cyclosporine, tacrolimus to prevent organ rejection Develop B cell lymphoma, usually w/ EBV in each tumor cell If immunosupp stopped- tumor can sometimes regress Post-Tx: Many EBV B cells, few EBV-specific T cells Congenital Immunodeficiency -Severe combined immunodef- often die w/ EBV lymphoma -X-linked immunodef- often die w/ EBV lymphoma (often boys) AIDS Lymphoma -Increased risk of lymphoma -~50% EBV-associated lymphoma X-linked agammaglobulinemia -NO B cells -NO EBV -NO B cell lymphoma **Protected** |
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EBV and other Tumor Associations
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NP carcinomas virtually always EBV-associated, regardless of geo
Tumors are more common in Cantonese, other southern chinese ethnic groups No evi of immunodeficiency Hodgkin's Disease EBV Ag Expression in 30% -DNA detected; RNA detected; Antigen expresion -Present at each tumor site, at presentation and relapse |
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Kaposi's Sarcoma
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Children in Africa- involving feet, legs
Old men in Mediterranean Organ tx recipients AIDS pts- esp MSM Most commonly involves skin (GI, lungs) Neovascular proliferation Purplish color from red cells in neovasculature KSHV = HHV8 Detected by PCR in B lymphocytes in seropositive indiv Does NOT immortalize B lymphocytes in vitro Carries several genes close mimics of human genes ** IL6 Transmission- early childhood in endemic regions (saliva) Sexual- MSM Patho of KS: KSHV infection required Immunocompromise |
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Primary Effusion Lymphoma
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B cells floating pleural or peritoneal fluid
Occurs in AIDS pts Dually infected by EBV, KSHV |
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Hepatitis
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Inflammation of the liver
Non-infectious causes Alcohol Acetomeniphen (Tylenol) Halothane Isoniazid (INH for TB) Other meds Shock, acute obstruction Infectious Causes Nonviral: Pneumococcal pneumonia, leptospirosis, sepsis, TB, histoplasmosis, ricketial infections, syphilis Viral: CMV, EBV, HIV, adenovirus Hepatitis Virus |
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Hepatitis Virus
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5 viruses
A to E HAV causes majority of acute viral hep in US Transmission: Fecal oral: HAV, HEV Sexual: HBV, HDV (A,E,C less) Blood: HBV, HDV, HCV (A,E less) Perinatal: HBV, HDV (HCV>HAV,HEV) B,C,D have envelope destroyed by bile- no fecal oral route possible Symptoms more often w/ A, B Persistence/Chronic infection w/ C Healthy liver-Fibrosis- Cirrhosis- Macronodular Cirrhosis- Hepatocellular carcinoma (risk increases w/ persistence of HBV, HCV) Lab Dx: Transaminase: ALT, AST (>10-100X normal) IgM antibody = acute infection, or past Neutralizing antibodies = recovery Viral particles = ongoing infection (protein, nucleic acid) Vaccine: HAV, HBV Rx: Acute: none, prevent secondary cases Chronic: HBV- INFa, laminvudine, adefovir, entecavir, tenofovir HCV- INFa, ribavirin |
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HAV
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IgM antibodies are markers of acute infection, typically detected for about 6 mo.
Picornaviridae, RNA virus NO Envelope (bile stable) Capsid proteins elicit universal neutralizing antibody Vaccine: YES |
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HBV
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Dx: When products of infectious agent or its nucleic acid detected, it implies ongoing infection (acute or chronic!) and infectivity
S gene and vaccination Lg, Mid surface antigens cccDNA and persistence: Replication- RNA nuclear import- repair-> ccc = completely closed circular DNA (very stable in host nucleus, can integrate and remain as resevoir) Virion # / Stability, transmission: VERY transmissable Genome: very small genome S gene makes surface antigen -3 proteins made -5 specificities, a determinant that elicits neutralizing antibodies -S gene put into yeast to make first recombinant vaccine |
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HDV
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DEPENDENCY issues- needs HBV
Uses HBV's envelope as its envelope |
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HCV
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HCV Replication
-Rapid turnover -Error prone replication *Genomic diversity *Make mistake at every base, every day, in every person Mutations- synonymous (silent) or nonsynonymous... Neutral or Lethal or Nonlethal Variants can evade adaptive immune system HCV persists; infectious for decades Persistence, 80% Resistant to treatment HCV vaccine dev Reservoir Antiviral drug dev. |
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HEV
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Incubation period avg 40 days
Case-fatality: PREGNANT WOMEN 15-25% Illness severity increases w/ age |
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Vaccine
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Any formulation able to elicit antigen specific protective immunological memory.
Classic- vaccine mediated protection based on exposure of an immunogenic agent to a host followed by natural development of immunity |
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Types of Vaccine formulation
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Live Vaccines: Formulations where the antigens are encoded by a genetic material (live, attenuated vaccines) and synthesized IN HOST.
-Infectious agent -Strong innate inflamm. responses (natural adjuvant) -Strong induction of all (B&T) adaptive responses and longer memory "INACTIVE" Vaccines: FOrmulations where the protein or polysaccharide antigens are directly injected into the host (innactivated vaccines, recombinant proteins, purified polysaccharides...) -Local antigen deposit and dist. to regional lymph nodes -Weak innate inflammatory response (requires addition of adjuvant) -Mainly induce antibody responses (weak CD8 cytotoxic responses) |
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Essential components of vaccine
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Appropriate presentation to immune system
(Route, B-cells, CD4 and CD8 T-cells) Immune stimulatory signals able to start innate immune responses and shape the adaptive effector mechanisms (Adjuvant) Antigenic epitope correlated w/ protection: B-cell, linear and conformational: T-cell CD4 and CD8 (Active principle) Approp. Presentation to imm. sys. B-cells: -Polysaccharides: CCD4-Independent antibodies (IgM) -Proteins: CD4 dependent antibodies (IgG) T cell: CD4: protein processed in clas II pathway CD8: protein expressed intracellular compartment and processed in class I pathway Adjuvant in clinical use (for inact. and recomb vaccines) Aluminum compounds |
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Basic mechanisms of vaccine action
VIRUS |
Act. of immune system to produce antigen specific B cell responses (Antibodies)
-Neutralization- block bio. fxn of antigen -Opsonization- accelerate clearance of antigen Act of immune system to produce T-cell responses (CD4+ T-helper and CD8+ cytolitic) -CD4+ cells- cytokine secretion to support B-cell and CD8+ cytolitic cell activation, proliferation, maturation and memory differentiation Neutralizing antibodies target surface envelope glycoproteins Cytotoxic T lymphocytes target cytoplasmic non-structural proteins |
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Protection: BACTERIA
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Opsonizing antibodies facilitate phagocytosis; target surface polysaccharides and envelope glycoproteins
Anti-toxin antibodies neutralize toxins by targeting toxins |
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CD4+ T lymphocytes in HIV infection
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CD4+ infection by HIV leads to cell death of infected and uninfected lymphocytes
CD4+ are central to immune response Natural history of AIDS- loss of CD4+ cells in peripheral blood, lymphoid CD4+ monocytes are targeted and traffic to tissues->specific tissue macs-> produced virus, cytokines Normal CD4+ = 1000 cells/ul AIDS < 200 cells/ul |
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Retroviruses
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Spherical w/ lipid containing envelope (sensitive to detergent)
Dense nucleocapsid core w/ viral RNA genome and Reverse Transcriptase enzyme Envelope: Surface glycoprotein (gp120 HIV) -highly glycosylated mediates interaction btwn virus and rececptor -contains epitopes for neutralizing antibodies and cytotoxic lymphocytes (CD8+) Transmembrane glycoprotein (gp41 HIV) -Anchors surface glycoprotein -mediates virus induced cell fusion Structure: Nucleocapsid constructed by core protein p24 (HIV) (antibody to p24 used in ELISA assay for HIV infection, quantitative) -2 copies of RNA genome, each with RT -Positive strand RNA -Genome: structural genees, viral proteins, proteins in viral envelope; pol gene- RT, RNase H, protease, integrase Replication: Virus Entry Virus Fusion Reverse Transcription Integration of viral DNA Txn of viral genes Viral protein expression and virus assembly Virus budding, Maturation |
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Virus Entry- HIV
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gp120 molecule on virus binds CD4 on cell-> conformational change in protein allows gp120 to interact w/ co-receptor on cells surface- interaction of gp120 causes conform. change in gp41 exposing hydrophobic domain that mediates fusion btwn virus envelop and cell memrane
Virion loses envelope, viral core enters cell Co-receptors = chemokine Co-receptor for T-cell tropic HIV = CXCR4 on T-cells and PBMCs Macrophage-tropic strains co-receptor = CCR5 on PBMCs and mac |
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Reverse Transcription- HIV
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Synthesis of dsDNA from RNA
RTase and tRNA primer at 5' end Reverse Txn- synthesis of dsDNA (RTase synthesizes - DNA copy RNase H degrades viral RNA and RTase makes = DNA ERROR PRONE |
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Integration of Proviral DNA- HIV
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Nucleocapsid w/ dsDNA transported to nucleus
DNA integrated by integrase Viral DNA replicated w/ cellular DNA Can remain LATENT |
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Productive Replication & RNA Transcription
Assembly and Maturation |
Cell contains approp. txn factors for virus to express viral mRNA and genomic mRNA
Viral DNA txn-ed into mRNA by cellular RNAPII 5' Capping AAAA-Tail Splicing Processing of Env polyprotein by viral protease in golgi Immature virion forms at membrane of cell ONce budded, viral protease cleaves Gag and Gag-Pol-> mature virion (infectious) |
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HIV Transmission
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Genital secretions
Blood highest conc'n Congenital transmission during gestation , during birth, from breast milk |
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Clinical Consequences: Acute Infections- HIV
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Enlarged painful lymphnodea, fever, rash, muscle ache, meningitis, lymphadenopathy, malaise
Productive replication in lymph nodes--> viremia and decline in CD4+ Acute infection-->elicits cellular & humoral response; virus in blood declines (killing by CD8+, NK, cell-mediated cytotoxicity. Neutralizing antibodies Virus Load: Measurement of virus by quantitating virion RNA by RT-PCR Level of virus (set point) = prognostic indicator of disease progression During clinically asymptomatic period, virus still present, CD4+ lymphocytes at normal level; virus replication in lymph nodes, spleen, and brain. FDCs trap virus, present antigens--> cellular recruitment-->hyperplasia |
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Development of Disease- HIV
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Over time, Steady decline in anti-viral immune responses, CD4+ lymphocytes,
INCREASE in viral load in blood Lymph node destruction (complete in AIDS); Opportunistic infections Susceptible, activated CD4+ lymphocytes continually recruited to lymphoid tissues, infected, and die **CD4+ loss throughout course of disease Problems: Immune suppression AIDS AIDS encephalitis AIDS dementia Interstitial pneumonitis |
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Pathogenesis of AIDS
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Depletion of CD4+ lymphocytes--> change in ratio of CD4/CD8
Exhaustion of stem cell pool Functional CD4+ lymphocyte abnormalities (HIV eliminates CD4 on cells, which is essential for signaling) HIV downreg. MHC class I expression on cells Infected monocytes (latent) spread infection to lung, brain, and bone marrow. Activation into macrophages--> virus txn, production AIDS is catastrophic failure of immune system |
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Treatment- HIV
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Highly active anti-retroviral therapy HAART
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Retrovirus Diversity
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High rate of mutation
RNA viruses in general higher rate b/c no proofreading fxn High level of viral diversity in population and in individual Antigenic variation |
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HIV Drug Resistance
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Selection or pre-existence of drug-resistant virus mutant =
short-lived effects of anti-viral drugs, difficult problem in HIV Rx design |
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HIV Latency
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Long-lived population of latently infected resting CD4+ memory T lymphocytes in peripheral blood containing HIV.
Can reactivate when HAAR Rx stopped Tissue reservoirs of CD4+ lymphocytes and macrophage. |
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Clinical Assays to Detect HIV
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Evidence of infection- presence of antibodies
Presence of virus- culture or PCR HIV serology- ELISA add pts serum to plastic wall containing HIV proteins. If antibodies present, they bind, bound IgG detected w/ enzyme rxn Positive result confirmed w/ Western Blot assay Real-Time PCR- highly sensitive; detects virus in plasma and CSF Can detect as little as 50 copies of HIV RNA in 1ml of plasma or CSF Measures virus, does NOT depend on immune response to virus to develop antibodies (like ELISA and W. blot) |
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Why no HIV vaccine?
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-Viral vaccines prevent disease caused by virus, not infection
-HIV vaccine should induce "sterilizing immunity" (prevent infection so no latently infected cells) -Natural infection w/ HIV-1 or HIV-2 does not protective immune responses that can be used to develop vaccine -HIV-1 exists as genetically diverse population of viruses- require multiple vaccine combos -HIV-1 infection generates nique quasispecies in each infected individual |
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Common Features of Herpesviruses
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Virus morphology
Viruses are ubiquitous Infection is often asymptomatic Common modes of replication (virus lifecycles have general themes) -ALL ESTABLISH LATENT INFECTIONS. (reactivation can produce disease) Genomes: HUGE! >100kb Genes: HUGE! >50 -Enzymes -structural genes -Non-structural genes |
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Herpesvirus Infection "Modes"
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Productive infection--> release of progeny virions "lytic infection"
Latent Infection: -No virion production -Acts as reservoir for recurrent disease -Recurrent disease occurs as consequence of: --renewed replication OR --Cell proliferation (limited to tumor-inducing gamma herpesviruses only) |
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Lytic Infection v. Latent Infection
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Lytic:
Viral envelope formed from NUCLEAR membrane Gene expression in Lytic: Immediate early: regulators of viral gene expression Early: proteins required for genome replication Late: virion structural proteins Gene Expression in Latency: RESTRICTED Infected cell types: Lytic: Many >2 Latent: Few; 1 or 2 (lymphocytes and neurons) |
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Herpesvirus Transmission
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Natural modes- skin, mucous membranes
(HSV-1, -2) skin, genital tract Secretions -oral -Respiratory tract (VZV) Transplacental (CMV) Iatrogenic Modes -transfusin -transplants (CMV) |
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General Concepts in Herpesvirus Disease
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High disease severity
-Primary Infection -Immune impairment Low Disease Severity -Recurrent infection -Immune competent Populations w/ severe infections: -Immunodeficient -Immunosuppressed -Fetus/newborns -Malnourished -Burn victims |
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Herpes Simplex Virus Disease
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Herpes labialis (lips)
Genital herpes Primary site- productive infection of epithelial cells -Retrograde transport- Secondary site of infection and latent infection: **sensory neuron -Reactivation, anterograde transport- Site of recurrent infection: productive infection of epithelia cells **Orolabial HSV- trigeminal ganglia **Genital HSV- sacral ganglia Common features of orolabial and genital herpes recurrence: Reactivation can be symptomatic (blisters) OR Asymptomatic |
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Genital Herpes
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Correlates w/ # sexual partners
Women more susceptible Transmission is commonly UNrecognized Asymptomatic shedding = COMMON Primary infections- often asymptomatic Recurrence: Symptomatic recurrence after yrs of silent infection Symptoms less severe than primary disease (shorter shedding time, fewer lesions) Recurrence severity: HSV-2>HSV-1 Factors affecting recurrence: Time since aquisition Virus type Immune status Transmission: Unknown- shedding rates have no impact on transmission Antiviral Efficacy: Acyclovir Reduces recurrences Reduces transmission |
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Other HSV Presentations
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Primary gingivostomatitis (gums, oral cavity, lips)
Herpes Whitlow HSV Keratitis- #1 cause of infectious blindness in developed world 2 pathogenic mechanisms: autoinoculation; trigeminal nerve opthalmic root infection after ganglion reactivation Dendritic ulcers |
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Neonatal Herpes
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Transmission through infected birth canal
-most women asymptomatic during labor Presentation during 1st 1-2 wks of life Three syndromes: -skin, eye, mouth (SEM) ----usually not fatal, but recurs ----30% develop neurologic sequelae -encephalitis -disseminated Occurrence of vesicles: SEM > CNS > Disseminated Cannot use absence of vesicles to rule out neonatal herpes! |
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Herpes Encephalitis
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Most common acute sporadic encephalitis
Primarily HSV-1 Classic Presentation: fever and focal neurologic deficits -temporal lobe involvement |
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Varicella-zoster Virus (VZV)
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Primary infection (Varicella)
-Chicken pox Sever disease -Teens/Adults at risk for varicella pneumonia -Immunocompromised & newborns ----life threatening pneumonia ----encephalitis ----progressive, disseminated varicella Herpes zoster (shingles) -reactivation in sensory ganglion -lesions localized to innervated dermatome -can disseminate in immunocompromised pts ----- >2dermatomes ------ across midline |
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Cytomegalovirus
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Infection usually asymptomatic
Disease can occur -Mononucleosis -Congenital infection -Recipients of solid-organ, bone marrow Tx, leukemia/lymphoma, AIDS CMV Mono: 79% EBV, 21% CMV Frequent manifestation of primary CMV in young adult Syndrome: fever, lymphadenopathy, lymphocytosis -exudative pharyngitis freq. absent Heterophil antiody negative Congenital CMV: Disease severity dependent upo maternal serostatus during preg. -primary maternal infection: severe symptoms in 25% of births -reactivation during preg.: usually asymptomatic at birth; late onset hearing loss |
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CMV in Immunocompromised Patients
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HIV: reactivation and disease when CD4 < 50
-retinitis -uncommon w/ HAART Bone Marrow Transplant -common presentation; pneumonia after marrow engraftment -prophylaxis w/ ganciclovir Solid Organ Transplant -HUGE problem -usually manifests as disease in allograft -Highest risk cases: CMV seronegative recipient receiving organ from seropositive donor |
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HHV-6 and -7
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Roseola infantum (exanthum subitum)- red cheek appearance in very young children
Febrile seizures common w/ roseola May see infectious mononucleosis, hepatitis, neurologic syndromes Transplant: fever, hepatitis, SKIN RASHES |
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Herpesvirus Diagnostics
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Viral culture (HSV from all sites except CSF)
Rapid antigen detection: lesions (VZV at JHH) Detection of nucleic acids: CNS disease, lesions (VZV at JHH) Antibody detection assay: utility is limited their than for mononucleosis useful in solid organ tx to id high risk pts |
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Live-replicating organism (Attenuated virus)
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General: Attenuation of the pathogenic properties and preservation of immunogenicity is not always possible
Ex: Varicella Virus Vaccine (VARIVAX) Formulation, Inoculation: The virus is unstable Requires stabilizers for viability Active Principle (Antigen) -Adapted in many different cell cultures Immune stim signals (Adjvant) -Org. naturally activae innate immune system; no additional adjuvant necessary Presentation to immune system: -Viral antigens produced by host and secreted w/ preserved conformational structure -Antigens access to MHC class I and II processing and presentation -Elicit good neutralizing antibodies, CD8, CD4 and memory responses |
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Live-replicating organism (Recombinant/Reassortment)
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General: Attenuation of the pathogenic properties by reassortment of bovine and human Rotaviruses genes using reverse genetics
Example: Rotavirus vaccine, oral, pentavalent Formulation/Inoculation: Virus is unstable; requires stabilizers Active principle (Antigen): 5 attenuated Rotavirus viral strains. Reassortants are propagated in Vero cells using cell culture tech. Immune Stim: Naturally activate innate immune system; no adjuvant required Presentation to the immune system: Viral antigens replicate in SI and secreted w/ preserved conformational structure Antigens access to MHC class I and II processing and presentation Elicit good neutralizing antibodies, CD8, CD4, and memory responses Mucosal IgA responses |
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Inactive/non-replicating Whole organism
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General: Require effective inactivation of pathogenic properties w/ preservation of immunogenicity
Ex: Hepatitis A vaccine (HAV) Antigen Presentation: Intra-muscular injection Active principle (Antigen) HAV is a formalin inactivated whole virus vaccine derived from an attenuated hepatitis A virus (HAV) grown in cell culture in human fibroblasts Immune Stim: Weak activation of innate immune systems; REQUIRE adjuvant (Aluminum hydroxyphosphate) MHC Presentation: Antigens access to MHC II processing and presentation Usually in multimeric antigenic form and induce good antibody responses Does NOT produced biologically relevant CD8 responses Elicits GOOD antibody memory response |
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Subunit- Polysaccharides
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General: Require purification of antigen, and inactivation of toxic properties
Does not require epitope mapping Ex: Miningococcal polysaccharide vaccine Formulation/Inoculation: subcutaneous; still complex mixture, requires stabilization Immune Stim: Stimulate innate immune system (TLR receptors) Active principle: Purified polysaccharide extracted from freeze-dried preparation of Neisseria meningitidis cells and separated from media by purification procedures Presentation to immune system: CD4 independent B-cell activation IgM production Short-lived antibody memory response Rapid decline in antibody titer |
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Subunit- Protein conjugated polysaccharides
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General: Require purification of the antigen, and inactivation of toxic properties
Does NOT require epitope mapping Ex: Conjugated meningococcal polysaccharide vaccine Formulation/Inoculation: Subcutaneous injection; still complex mixture, and require stabilizers Immune stim: Stimulate innate immune system (TLR receptors) Active Principle: Purified polysaccharide extracted from freeze-dried prep of N. meningitidis cells and separated from media by purification processes Diphtheria protein is purified and inactivated w/ formalin, polysaccharides are covalently linked to toxoid and purified Presentation to immune system: Fxnl cooperation btwn strong CD4 responses against diphtheeria toxoid and polysaccharides CD4 dependent B-cell activation; IgG production Longer lived antibody memory response |
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Subunit- Recombinant Protein
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General: Protein antigen expression in genetically modified heterologous organism
Ex: Hepatitis B Vaccine Formulation/Inoculation: IM Immune Stim: NEEDS adjuvant aluminum hydroxide Active Principle: Purified surface antigen of virus obtained by culturing genetically engineered Saccaromyces cervisiae cells, which carry surface antigen gene of Hep B virus. ANtigen purified and formulated as suspension of antigen adsorbed on aluminum hydroxide Presentation to Immune System: CD4 dependent B-cell act.; IgG production Longer lived antibody memory response |
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Vaccine Use
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Active Immunity:
Protection produced by person's own immune system Long lasting Passive Immunity: (can interfere with vaccination) -Protection transferred from another person or animal as antibody -Temp protection, wanes w/ time -Passive immunity (transplacental IgG antibodies) passsed from mother to child interferees w/ vaccination. Child vacc scheduled to avoid neutraliztion of vaccine by passive serum |
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Immunization during Pregnancy
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Protects mother & infant
Transplacental antibodies transfer safer and less expensive then Ig therapy Factors influencing antibody transfer to placenta: Time between vaccination and delivery IgG levels and subclass (IgG1=IgG3 >IgG4>IgG2) IgM, IgA, IgE do NOT cross placenta Gestational age (33 weeks, IgG maternal = IgG fetal; 40 weeks, IgG fetal>IgG maternal) Maternal antibodies protect infant Maternal antibodies neutralize live attenuated vaccines and influence immunization schedule |
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Immunological Differences in neonates
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Immunological immaturity:
immature lymphoid organ arch. (rec immunization 8 weeks post-natal) CD4+ helper T cel responses: limited secretion of INF gamma Innate: limited T-cell independent responses Impaired TLR3 and 9 Delayed maturation of dendritic cells -limited IL-12 responses Limited activation of CD4+ cells Delayed and limited induction of germinal centers (low Ab responses) Influences of maternal antibodies -Epitope specific -Does not affect T cell priming Immunize ASAP and boost as needed |
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Immunological differences in Elderly
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Cognate functions
Thymic regression -reduced naive T cell population CD4+ helper T cell responses -Impaired TRC-MHC signaling CD8+ Cellular Senescence Innate -Deregulation of Macrophage fxn Impaired signaling and antigen presentation |
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HBV Antiviral:
Alpha-interferon |
Potent inhibitor of HBV
Used to treat chronic active HBV Mech: Activates Jak/STAT signal transduction pathway-->nuclear translocation of protein complex that interacts w/ genes containing IRES Genes encode proteins that help cell resist viral infection by interfering w/ penetration, uncoating, RNA txn, translation, virus assembliy, release **Inhibition of viral protein synthesis Bioavailability: Poor orally, good IM or subcutaneous Toxicity: Acute influenza-like symptoms (fever, fatigue, chills, headache, muscle aches), sometimes neuropsych probs, limit tolerance of long-term rx REsistance: Tolerance to drug develops in most pts. HBV "terminal protein" interferes w/ action of interferons by blocking signal transduction |
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HBV Antiviral:
Lamivudine (3TC) |
Nucleoside analog that inhibits HIV reverse transcriptase AND HBV RT b/c of similarities btwn enzymes
Mech: Cellular enzymes convert drug to triphosphate, which competitively inhibits HBV DNAP causing chain termination Bioavailability: 80% absorbed orally Toxicity: Negligible Resistance: Many resistant strains have mut. in viral DNAP Discontinuing drug --> rebound HBV viremia to pretreatment levels 14-32% of immunocompetent pts have resistance w/in 1 year, 50% w/i 3 yrs. |
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Influenza A, B, avian flu Antiviral:
Amantadine & Rimantadine |
Mech: Primary effect at early infection; inhibits essential ion channel in virion envelope formed from viral protein M2.
M2 channel- mediates reduction pH in virion, essential for uncoating RNA genome. Drug binds specific aa lining channel, preventing ion flow Amantadine dec pH in golgi at late infection--> premature conformational change in viral hemagglutinin protein (HA), which deceases release of infectious particles Bioavail: orally 50-90% for A; >90% for R Resistance: Occurs RAPIDLY. 30% of treated people shed resistant virus w/in 5 days. Drug resistance mutants retain fitness, but remain sensitive to Ribavirin (broad-spectrum, nucleoside analog toxic) |
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Influenza A, B, avia flu Antiviral
Zanamivir Oseltamivir (Tamiflu) |
Inhibitors of viral Neuraminidase (NA) which cleaves terminal sialic acids from glycoproteins, glycolipids, and proteoglycans
Cleaving sialic acid promotes effective viral spread in resp tract by preventing aggregation/attaching to sialic acid receptors on resp epithelium Drugs active in prophylaxis and treatment Mech: Competitive, reversible inhibitors of NA. Active site pocket of viral NA has binding sites for glycerol and carboxylate groups of sialic acid. Zanamivir is analog of sialic acid Oseltamivir, prodrug of transition state analog of sialic acid Minimal toxicity Bio: poor for Zanamivir; given IV or aerosol spray; Good for Oseltamivir, given orally Resistance: Development of resistance to Z and O is inefficient. |
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Herpesvirus Antivirals:
Acyclovir (ACV) |
Mech: Inhibits DNA synthesis
Initial phosphorylation to ACV-P by viral TK (high affinity for ACV) ACV-3PP by cellular kinase ACV-3P competitively inhibits viral DNA polymerase. Incorporated into DNA causing chain termination Spectrum of activity: HSV-1, HSV-2, HZV Bio: ACV 10-30% orally; Valacyclovir- higher oral availability Tox: well tolerated, some nausea, diarrhea, rash, headache Resistance: Leading cause of resist= mutation of viral TK, ability to phos. ACV reduced Resistance from mut. in viral DNAP, decreases incorporation of ACV-3P into DNA |
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Herpesvirus Antiviral:
Ganciclovir |
Analog of guanosine, activity against CMV
Mech: GCV converted to monophosphate by viral kinase; tri-phos by cellular kinase Potent inhibitor of DNAP; inhibits incorp of GTP into DNA GCV-3P not chain terminator, but inhibitory effect is due to inhibition of CMV DNA elongation Bio: 10-20% orally Tox: Bone marrow progenitor cells inhibited Resistance: mutations in kinase (UL97 or CMV) making it unable to phos. GCV. |
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Herpesvirus Antiviral:
Foscarnet |
Analog of pyrophosphate that is inhibitory for all herpesviruses and HIV.
Only nonnucleoside replication inhibitor for herpesviruses Mech: reversibly blocks pyrophosphate binding site on DNAP; inhibits cleavage of pyrophos from dNTPs during DNA chain elong. Selective tox: viral DNAP more susceptible Bio: 9-17% orally Tox: Accumulatese in bone, causes kidney toxicity, so used for life-threatening infctions Resistance: mutations in viral DNAP. Freq.works against ACV and GCV-resistance mutants |
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Herpesvirus Antiviral:
Fomivirsen |
Phosphorothioate-based 21-mer anti-sense oligonucleotide that interferes w/ essential steps in CMV replictaion.
Mech: Anneals w/ "sense" strand of RNA encoding an essential major immediate-early viral protein whose fxn required for virus rep. Bio: Requires injection into eyes Toxicity: Produce indicated for local treatment for CMV retinitis in pts w/ AIDS who are intolerant of or have contraindication to other Rxs for CMV retinitis, or who failed other Rxs. Expensive Resistance: Reported |
