Animal And Plant Viruses

Question 1

What are the outcomes of animal virus infections

Answer 1

Acute infection
Persistent infection (slow, chronic, latent, late complications following acute infections)
Cell transformation

Question 2

What are acute infections

Answer 2

Short duration and host normally develops lost lasting immunity

Question 3

Explain damage to the host

Answer 3

Cytoplasmic effects - syncytia (multinucleate cell) and inclusion bodies

Question 4

Types of animal viruses and composition

Answer 4

Orfvirus Ebola virus and vaccinia virus
3 orders ( -virales)
21 families (-viridae)
14 RNA virus families and 7 DNA families
Families divided into genera (-virus)

Question 5

Explain the life cycle of the retrovirus

Answer 5

Penetration and uncoating of viral RNA
translation of +RNA
Synthesis of RNA to serve as a template for synthesis of new +RNA
Synthesis of +RNA
Assembly of new virus particles

Question 6

Explain the viral host range

Answer 6

Usually very narrow and can be broadened (phenotypic mixing and genetic reassortmrnt)

Question 7

What is phenotypic mixing

Answer 7

Viruses switch protein coats

Question 8

What is genetic reassortment

Answer 8

Occurs in viruses with segmented genomes and leads to an antigenic shift

Question 9

What must animal viruses have

Answer 9

Must have living cells ( cells and tissue culture, embryomated chicken eggs and live animals)

Question 10

How to plant viruses spread

Answer 10

Enter the wound or insect bite and spread from cell to cell through plasmodesmata

Question 11

What are 2 examples of plant viruses

Answer 11

Wheat mosaic and Tabacco mosaic virus

Question 12

What can tissue and cell cultures contain

Answer 12

Primary culture- tissue prepared directly from animal and tumour cell lines- immortal cell lines

Question 13

Explain the quantitation of animal viruses

Answer 13

Plaque assay, microscopic assay, hemagglutination assay (useful for tittering flu virus) and ID50 and LD50 assay (dilution at which 50% of inoculated host cells are infected or killed)

Question 14

Explain the multiplication cycle of an animal virus

Answer 14

1. Attachment - glycoprotein spike bind to receptors on host cell surface
2. Entry - fusion of cell membrane with viral envelope
3. Uncoating - nuclei acid is released from nuclocapsid
4. Replication of nuclei acids and proteins - DNA enters the nucleus and is transcribed, RNA is exported to cytoplasm and translated, DNA is replicated in the nucleus and viral DNA is inserted into the host genome
5. Maturation/ assembly- new nucleocapids self assemble
6. Release of the virus