Virological Methods

Question 1

What are the 5 main lab methods to confirm viral diagnosis?

Answer 1

1. Isolation/growth
2. Cytopathic effects (CPE)
3. Electron microscopy
4. Detect viral components (e.g., PCR, ELISA)
5. Evaluate immune response (Serology).

Question 2

What is transfection?

Answer 2

Infection of mammalian cells by bare viral nucleic acid.

Question 3

What is transformation (in virology)?

Answer 3

A stable, heritable change in a cell’s genetic makeup and phenotype (often to neoplastic) caused by a virus.

Question 4

What are permissive cells?

Answer 4

Cells that support the complete virus life cycle, producing infectious virus.

Question 5

What are non-permissive cells?

Answer 5

Cells that permit none of, or only part of, the virus life cycle.

Question 6

What is a defective virus?

Answer 6

A virus that cannot complete its replication cycle without a “helper” virus (a complete virus) also infecting the cell.

Question 7

What is a cytopathic effect (CPE)?

Answer 7

Observable damage or change to a cell resulting from viral infection.

Question 8

What are 4 common cytopathic effects?

Answer 8

1. Proliferation (transformation)
2. Cell death and lysis
3. Syncytia (cell fusion)
4. Inclusion bodies.

Question 9

What causes syncytia (multinucleate giant cells)?

Answer 9

Fusion (F) proteins from enveloped viruses, causing adjacent cell membranes to fuse.

Question 10

What are inclusion bodies?

Answer 10

Aggregates of viral proteins.

Question 11

What is an example of an inclusion body for Herpes Simplex Virus (HSV)?

Answer 11

Cowdry type A bodies.

Question 12

What is an example of an inclusion body for Rabies virus?

Answer 12

Negri bodies.

Question 13

What is the “serial dilution end point method” used for?

Answer 13

Determining the infectious units of a virus (live cultivation).

Question 14

What 5 things can be observed to determine infectious units?

Answer 14

1. Plaque formation (cell lysis)
2. Focal cytopathic changes
3. Focal proliferation of cells
4. Pock formation (in embryonated eggs)
5. Infection in animals.

Question 15

What are the 3 main methods for virus cultivation?

Answer 15

1. Tissue culture
2. Embryonated egg
3. Intact animal.

Question 16

What is hemagglutination?

Answer 16

A method to enumerate viral particles where viruses bind red blood cells into a lattice, preventing them from settling.

Question 17

What is the principle of the complement fixation test?

Answer 17

A virus-antibody complex consumes complement, which is then unable to lyse added (sensitized) red blood cells.

Question 18

What is the principle of direct fluorescent antibody?

Answer 18

An antibody (with a fluorescent tag) binds directly to a viral antigen in a sample.

Question 19

What does a Western blot detect?

Answer 19

Viral proteins (run on a gel and visualized by antibody).

Question 20

What does ELISA (Enzyme-linked immunosorbent assay) detect?

Answer 20

Viral products (antigens) or antibodies to those products.

Question 21

What does PCR (Polymerase Chain Reaction) amplify/detect?

Answer 21

Specific viral DNA regions.

Question 22

What does RT-PCR (Reverse Transcriptase-PCR) amplify/detect?

Answer 22

Specific viral RNA (by first converting it to DNA).

Question 23

What are 7 methods to measure antibodies in a patient’s serum?

Answer 23

1. Neutralization
2. Complement fixation
3. Hemagglutination-inhibition
4. Latex agglutination
5. ELISA
6. Indirect fluorescent antibody
7. Western blot.

Question 24

What are 3 mechanisms of viral neutralization by antibodies?

Answer 24

1. Hinder absorption to cells
2. Stabilize capsid (prevents uncoating)
3. Inhibit membrane fusion/entry.

Question 25

What are localized infections?

Answer 25

Viral multiplication and cell damage are localized near the site of entry.

Question 26

What are the 5 steps of a disseminated infection?

Answer 26

1. Local multiplication 2. Spread to lymphatics/blood (primary viremia) 3. Multiplication at secondary sites 4. Secondary viremia 5. Infection of the target organ.

Question 27

What is the incubation period?

Answer 27

The time from infection to the onset of symptoms (often asymptomatic during viral spread and multiplication).

Question 28

What are inapparent infections?

Answer 28

Asymptomatic viral infections.

Question 29

What are acute infections?

Answer 29

Virus infects the host, and disease ensues shortly after.

Question 30

What are latent infections?

Answer 30

Virus particles are not demonstrable but reappear during recurrences; viral nucleic acid is always present. (e.g., Herpesviruses).

Question 31

What are chronic infections?

Answer 31

Virus is always demonstrable and often shed; infected cells produce virus but may grow and divide. (e.g., Hepatitis B).

Question 32

What are 4 key host defenses against viral infections?

Answer 32

1. Virus neutralization by antibodies 2. Cell-mediated immunity (CD8+ cytotoxic T-cells) 3. Interferons (alpha and beta) 4. Natural Killer (NK) cells.

Question 33

How do interferons (Type 1) protect nearby cells?

Answer 33

They bind to uninfected cells, stimulating them to turn on genes for antiviral proteins that block viral reproduction.

Question 34

What are 6 methods for the control of viral diseases?

Answer 34

1. Prevention of transmission 2. Public health surveillance 3. Education 4. Isolation 5. Passive immunization (immunoglobin) 6. Active immunization (vaccines).

Question 35

What is the immunity duration difference: Attenuated vs. Inactivated vaccines?

Answer 35

Attenuated: Many years. Inactivated: Usually less.

Question 36

What is the antibody type difference: Attenuated vs. Inactivated vaccines?

Answer 36

Attenuated: IgG & IgA (mucosal). Inactivated: IgG only.

Question 37

What is the cell-mediated immunity difference: Attenuated vs. Inactivated?

Answer 37

Attenuated: Good. Inactivated: Poor.

Question 38

What is the reversion to virulence risk: Attenuated vs. Inactivated?

Answer 38

Attenuated: Rarely. Inactivated: No.

Question 39

What are 3 approaches to the treatment of viral diseases?

Answer 39

1. Symptomatic care 2. Immune serum (passive immunization) 3. Antivirals.