Virology A1 Lecture 1: Basic Virology

Front 1

Describe the basic viral characteristics:

1) Size
2) Metabolism
3) Protein production
4) What is the only way they can multiply?

Back 1

1) Small - 10-100 nm, invisible with light microscope
2) Metabolic inactivity, no intrinsic metabolism - obligate intracellular parasites
3) Made by host cell only
4) Can only multiply in living cells

Front 2

What is a viral nucleocapsid made up of?

What are viral envelopes made up of?

What are the different shapes of viruses?

Back 2

1) Nucleic acid core of DNA or RNA
2) Capsid (protein shell, repeating units of capsomere proteins)\\

Envelopes made up of host cell lipoproteins.

Icosahedral (20 sided solid soccer ball triangles), helical (tubular, spiral capsid), complex (retroviruses)

Front 3

Enveloped virus:

1) What is the envelope made out of?
2) What is on the outside of the envelope?
3) Where is the envelope located?
4) What is the function of the envelope?

Back 3

1) Host cell lipoproteins
2) Viral spikes
3) On the outside of the nucleocapsid
4) Evade immune system (can downregulate MHC class I), facilitate docking entry. Spikes determine the specificity

Front 4

What are the different types of viral spikes?

Back 4

Hemagglutinin (H in H1N1)
Neuraminidase (N in H1N1)

Front 5

What are syncytial viruses? What kind of viruses are they akin to?

What kind of viruses are naked viruses akin to?

Back 5

Enveloped viruses that can fuse with neighboring cells, create fusion cells with multiple nuclei. Akin to lysogenic - bud off a few at a time, infectivity rate is slower.

Naked viruses akin to lysogenic viruses. One cell makes thousands of infective viral particles, which infect many cells. Exponential growth in number.

Front 6

What is a pathological sign of enveloped viruses?

Back 6

Syncytia - giant enveloped multinucleated cells.

Front 7

Most human RNA viruses are what shape?

All human helical viruses are?

Back 7

Helical

All human helical viruses are enveloped

So most human viruses are enveloped.

Front 8

What is the symmetry and genetic makeup of the rabies virus? What does it infect?

Back 8

Helical, enveloped, ssRNA. Neurons(retrograde transport)

Front 9

What are the different options for the viral genome?

Back 9

DNA or RNA
Single stranded or double stranded
Linear or circular

Front 10

Most human RNA viruses are?
Most human DNA viruses are?

Back 10

Helical, ssRNA, + or - sense
dsDNA

Front 11

DNA viruses are everything except:

What are the DNA viruses?

Back 11

Naked ssDNA

PHAD: papova and pox, herpes, adenovirus

Front 12

RNA viruses are everything except:

Back 12

Enveloped dsRNA

Front 13

Where are the bulk of viral proteins found?

What proteins are found inside the nucleocapsid?

Back 13

In the capsid (protective sheath)

Enzymes for - strand RNA viruses, HIV viruses or retroviruses

Front 14

DNA viral replication:

1) Where does it occur? What do you see? Ex of a DNA virus?

RNA viral replication:

1) Where does it occur? What do you see? Ex of a RNA virus and its characteristic feature?

Back 14

Occurs in the nucleus, you see intranuclear inclusions. Herpes simplex

Occurs in cytoplasm, see cytoplasmic inclusions. Rabies (negri bodies, or dark bodies in the cytoplasm)

Front 15

7 steps of viral replication

Back 15

A PUTS AR

1) Adsorption - specific receptors bind either capsomeres (naked virus) or envelope glycoproteins (enveloped virus)
2) Penetration - endocytosis, fusion, translocation
3) Uncoating/eclipse
4) Transcription
5) Synthesis of viral components
6) Assembly
7) Release of virions

Front 16

Viral range and tropism: what can they be restricted to? Examples?

Back 16

Host range - can be restricted to certain species

Tissue tropism - can be restricted to receptors on specific cell types - neurotropic, lymphotrophic. Epstein Barr binds CR2 (B cells)

Front 17

What are the three main mechanisms for penetration and uptake of viruses?

Back 17

1) Endocytosis - route for successful infection, can prevent infection by other viruses

2) Fusion - envelope merges with membrane, releases capsid

3) Translocation - non-enveloped viruses can cross membrane, viropexis

Front 18

What happens during the uncoating/eclipse period?

What helps release capsid proteins?

Back 18

Nucleocapsid uncoated, infective viral particles are unseen

Endosome/lysosome proteases/acid can release capsid proteins

Front 19

Viral replication:

DNA viruses - where are they transcribed and translated? What do they use for transcription?

RNA viruses - where are they transcribed and translated? What do they use?

What is the difference between + strand RNA viruses and - strand RNA viruses?

Back 19

DNA viruses transcribed in nucleus, brought to cytosol for translation. Uses host DNA dependent DNA polymerase.

RNA viruses - transcribed in cytosol, translated by ribosomes in cytosol. Use VIRAL RNA dependent RNA polymerase. + strand viruses don't need to bring this with them.

+ strand RNA viruses act as mRNA, SUFFICIENT TO INITIATE INFECTION, are ready for translation by ribosomes, directs RNA dependent RNA polymerase.

- strand: genome not infectious alone, need viral RNA dependent RNA polymerase associated with nucleocapsid to change them into + form that's ready for translating.

Front 20

What are the two types of viral components that must be synthesized during viral replication?

Back 20

1) Structural components - proteins to package nucleic acid, packaging, capsid, and envelope proteins

2) Non-structural components - enzymes involved in viral replication, ie RNA-dependent RNA polymerase

Front 21

What is viral assembly? Where does it occur?

Back 21

Assembly of procapsid prior to release.

DNA virus in nucleus, RNA virus in cytoplasm, enveloped viruses in plasma membrane.

Front 22

What are the two ways in which viruses are released?

Back 22

1) Gradual - enveloped viruses, budding
2) Sudden - lysis/cellular rupture

Front 23

What is a virion?

Back 23

Complete virus particle, with a genome, capsid, with or without envelope. Outside of the cell, it's infective

Front 24

Where can viruses be grown, and how long does this require?

Back 24

Only on living cells, requires days to weeks

Front 25

What is the cytopathic effect? What kind of viruses cause them?

CPE of:

HBV:
Herpes simplex/herpes zoster
****Hep B, hepatocellular carcinoma

Back 25

Characteristic damage (LYSIS AND DEATH) made by a certain type of virus, especially seen in tissue culture. Naked viruses.

HBV: minimal CPE, most damage caused by immune response

Herpes simplex/herpes zoster - persistence/latency

Hep B/Hepatocellular carcinoma: TRANSFORMATION of cells in culture

Front 26

What are the four methods of directly examining viruses?

Back 26

1) Antigen detection - immunofluorescence, ELISA,

2) E- microscopy - examines morphology of virus particles

3) Light microscopy - histological appearance, syncytium formation, inclusion bodies

4) Viral genome detection - hybridization with nucleic acid probes, PCR

Front 27

You do immunofluorescence and you see the fluorescent tag concentrated around the nucleus. What kind of virus is it?

Cytosol?

Back 27

DNA.

RNA (rabies)

Front 28

What two diseases cause syncytium formation, and what lab method would you use to directly examine it?

Back 28

Respiratory syncytial virus (RSV) and measles, light microscopy

Front 29

Where do viral inclusions bodies tend to be located? Give examples of what these cells are called for certain diseases.

What do the inclusions of CMV look like?

Back 29

In nucleus of cells infected with DNA virus (Tzank cell, herpes virus), and in cytoplasm of cells infected with RNA virus (negri bodies: rabies)

CMV inclusions = "owl eyes", large cells, intranuclear inclusions, prominent chromatin margination surrounding halo

Front 30

What does serology detect in viral infection?

What are the three types of serology that you can do?

Back 30

Rising titers of antibody between acute/convalescent stage, or detection of IgM in primary infection

Complement fixation, immunofluorescence, neutralization

Front 31

What are the four main routes of entry for a viral infection? Give some examples of diseases that get through each.

What is the incubation period for influenza? Hep B?

Back 31

1) Respiratory tract (rhinovirus, measles)

2) Skin (papillomavirus, rabies)

3) GI tract (polio, hep A, rotavirus)

4) Genital tract (papillomavirus, HIV, herpes)

Incubation period for influenza = 1-2 days. Hep B = 50-150 days

Front 32

What kind of cellular response is there in response to viral infection?

Back 32

Humoral response - IgM and IgA made

Virus infects cell, proteins synthesized in cytoplasm, bound by MHC I in ER, peptides transported by MHC I to cell surface.

Cytotoxic T cells come release perforins to form transmembrane pores, granyzmes (serine proteases) to activate nuclease and initiate apoptosis. Cells don't lyse.

Front 33

1) What kind of diseases do prions cause?

2) What kind of tissue do they infect?

3) Are prions viruses? Do they contain DNA or RNA?

3a) How long are the incubation periods? What kind of diseases do they cause?

4) What is the normal form of prions? Abnormal?

5) What does the abnormal form do?

6) Examples of prions diseases?

7) How are prions transmitted?

Back 33

1 TSE - transmissible spongiform encephalopathies

2) Infect nervous tissue

3) Not viruses, don't contain RNA or DNA

3a) Extremely long incubation periods, cause long-term, chronic illness

4) Normal form = PrPc, abnormal = Prpsc

5) Abnormal form resists destruction, converts other proteins into abnormal form

6) Kuru, Crutzfeld Jacob,

7) Hereditary (rare), iatrogenic (rare), consumption of infected meat (mad cow)