Multiplication of Viruses Part I

TRUE OR FALSE

All viruses kills the cell they infect

FALSE

Tumor viruses don't kill the cell

Structural changes in the host cells that are caused by viral invasion is called?

Cytopathic Effect

A large cell like structure formed by the joining together of two or more cells is called

Syncytium

Which virus can form syncytium ?

Measles virus

What was the first assay used to detect viral infectivity in a DNA virus known as Vaccinia virus

CAM Pock-Assay

Vaccinia virus is a non-pathogenic form of

Small pox virus

How was CAM Pock-assay carried out?

1. First infect the aliquot of vaccinia virus into the chorioallantoic membrane

- Pock lesions would form where the virus infected

- you can count the pock

What limitations did CAM Pock-assay have?

not many virus form pock or lesion. on the chorioallantoic membrane

What is the most accurate and widely used test to measure the number of infectious particles?

Plaque assay

What are the steps for Plaque assay?

1. Grow cells that are susceptible to virus in culture plate.

2. The membrane of cell culture is grown to full confluence.

3. Growth medium is decanted and cell cultures are inoculated with aliquot of seal dilution of virus stock

4. After inoculating, culture dish is overlayed with agar

5. Neutral red stain is added to the agar.

6. Neutral red stain is taken up bye the viable cells.

7. Dead cells form plaque and releases the neutral red stain and will look amber in color

8. The plaques are counted

Why is agar added to the culture dish?

To inhibit the movement of newly released virus particles.

Why is plaque assay considered to the most effective one?

Because it has shown each of the plaque is initiated or can be initiated by infection of a single cell with a single virus particle.

What is Multiplicity of Infection (MOI)?

Ratio of number of infectious particle per cell.

How can viral titer be calculated?

(Mean # plaque/mL)*( Reciprocal of dilution)

What is the significance of the Poisson distribution?

It measure the number of plaque cells infected based on MOI

TRUE or FALSE

An increase in MOI means a decrease in cells infected

FALSE

Answer: increase

A high MOI means?

All cells to be killed

What kind of line can you get in one-hit kinetics and what is the slope of the line?

Straight line with a slope go one

it shows a direct proportion between the plaque and the concentration of virus inoculated.

What does end point titration assay measure?

How far can you dilute the viral suspension and still see the end point.

What is used as the end point in end point titration ?

Cytopathic effect

Who came up with calculating 50% in vivo endpoint titration?

Reed and Muench

TRUE or FALSE

Endpoint titration can be done in vivo and in vitro

TRUE

What can endpoint titration be used to quantify?

Viral infectivity

What is the chickenpox vaccine?

Virivax

What is the shingles vaccine?

Zostavax

What is the vaccine for measles, mumps, and rubella?

MMR II

Varicella vaccine is titrated using

Plaque assay

A 0.5 mL dose of Varicella vaccine contains how many plaque-forming units (PFU)?

Minimum of 1350 PFU

A single dose of zoster vaccine contains how many PFU?

Minimum of 19,400 PFU

What does the one-step growth curve do?

Used to make determinations about the life cycle of a virus on a particular host.

The one-step growth curve is only applicable to?

Large DNA viruses such as herpes viruses, Adenoviruses and pox viruses

Why is the one-step growth curve only applicable to large DNA Viruses?

Because the steps in multiplication of small viruses overlap each other.

What are the early period steps in one step growth curve?

1. Virus attaches to cell

2. Virus penetrate

3. Virus uncoated

4. Viral early genes are expressed

Which period corresponds to the period that follows uncoating of virus and precedes the appearance of intracellular progeny virions?

Eclipse period

What do early viral genes encode?

Enzyme and regulatory proteins

What is the late period in One-step Growth curve categorized by?

Structural proteins

What does structural proteins include?

Capsid protein and proteins that are inserted onto the the envelope of virus

The One-Step Growth Curve

A virus without a genome is _____

dead

What are the steps in Viral Replication?

1. Recognition of target cell

2. Attachment

3. Penetration

4. Uncoating

5. Macromolecule synthesis

6. Assembly of virus

7. Budding of enveloped virus

8. Release of virus

What are two things required for viral attachment?

- Viral attachment protein and cell receptor that is compatible with the viral attachment protein