Viral Infectious Cycle and Virology Methods

Question 1

What does a cell need to take up a virus and allow the virus to replicate?

Answer 1

It needs to be susceptible and permissive

Question 2

What are susceptible cells

Answer 2

• functional receptor for the virus

Question 3

What are permissive cells?

Answer 3

• allows the virus to replicate

Question 4

What are resistant cells?

Answer 4

• cells that do not have any receptors

Question 5

What are the hosts used for viral replication in the lab?

Answer 5

• Whole animal hosts
• non-human hosts
• replicates human response but is very costly
• need smaller hosts like rodents
• viruses to replicate unfertilized chicken eggs
• composed of multiple cell types
• still used to replicate the influenza virus - making the flu vaccine

Question 6

What are cytopathic effects

Answer 6

• the different changes that a virus induces inside a cell

Question 7

What are some examples of CPE

Answer 7

• cell lysis
• syncytia
• transformation

Question 8

What are syncytia?

Answer 8

• the fusion of adjacent plasma cell membranes

- results in a multinucleated array of cells

Question 9

What is transformation?

Answer 9

• cells that are no longer flat but divide uncontrollably to become piles of round cells

Question 10

How to measure infectivity?

Answer 10

• plaque assay; first used for bacteriophage (a virus that infects bacteria)
• agar plate; bacterial lawn
• an area, where bacteria have been infected with virus, are plaques
• in these areas, bacteria are replicating the virus
• count number of plaques to establish plaque-forming units (pfu/ml)

Question 11

What is the general idea when we measure infectivity?

Answer 11

• add a virus to cells
• overlay cells with a gel-like substance (agar)
• when infected cells release progeny
• the spread is halted by gel

Question 12

Explain the concept of the particle-to-PFU ratio

Answer 12

• it’s the number of virus particles per number of infectious particles
• smaller the ratio is, the more infectious the virus be
• large ratios mean that they are less infectious

Question 13

What is the transformation assay?

Answer 13

• certain viruses do not form plaques but form foci
• Rous Sarcoma Virus (RSV) forms foci
• can count foci and get foci forming units per/ml

Question 14

What is the hemaglutination assay?

Answer 14

• certain viruses contain proteins that bind to red blood cells
• if a sample contains viruses, they bind RBC and form a distinct lattice which coats the side of the tube
• lack of virus results in RBCs forming a “clot”

Question 15

What is viral enzyme activity?

Answer 15

• retroviruses (such as HIV) contains active enzymes such as reverse transcriptase (RT)

Question 16

What is immunostaining?

Answer 16

• only checking if virus proteins are present

- antibodies can be linked to phospho tags

Question 17

What is immunoblotting?

Answer 17

• denature all proteins and separate them

- antibodies to tag viral proteins

Question 18

How is sequencing used in physical measurement?

Answer 18

• useful for low viral abundance genes
• the exponential growth of gene product
• can be compared with other sequences in databases

Question 19

How are fluorescent proteins used in physical measurement?

Answer 19

• add to check if cells are infected and to see what is happening in the cell