Viral Persistence 1

Question 1

Req for persistence

Answer 1

Evade host imm d

Equilibrium between virus and host the breakdown of which can lead to cell injury and disease

Question 2

Types of infection

Answer 2

Acute
Latent
Chronic
Chronic (acute that becomes chronic with recurrent shedding)
Acute occassionally chronic
Slow

Question 3

Levels of persistence

Answer 3

In pop
In host
In cells

Question 4

Flu antigenic variation

Answer 4

Via antigenic drift and antigenic shift cause virus ability to persist in a pop that can mount a large vigorous imm resp

Question 5

Flue antigenic shift

Answer 5

Varied HA and N antigenicity is basis of classification of flu subtypes
New subtype intro to pop can cause a pandemic

Question 6

Flu antigenic shift mech

Answer 6

Two strains coinfect the same cell. So segments from both viruses being tepl in cell and assembly and budding can result in reassortment of the segments into diff combos so can have a human infecting virus with a new Ha or N, so a new subtype

Question 7

Flu antigenic drift

Answer 7

Ability to persist and cause epidemics is freq mutation as it is an RNA virus so uses error prone RNA pol causing changes in antigenicity of glycopro and are selected for by imm syst

Question 8

EIAV persistence in host

Answer 8

Lentivirus
Fever anemia weight loss progressive weakness after acute phase symptoms subside and animal appears to recover but sometimes there is persistent viremia and a 2nd attack with a differ variant occurs
Imm selects for new strains caused by antigenic drift that can then evade inm resp as Ab to original infecting strain is no longer complementary. Each successive isolate completely replaces previous strains (in visna virus drift occurs but strains coexist)
So evade Ab and cytotox t cells due to mutation in peptide complexed to MHCc1 recog by TCR

Question 9

Advantage to virus of persist in host not in pop

Answer 9

Without outside reinfection the min viral pop size to ensure persist within pop is much higher than in host

Question 10

Persistance at immunopriveleged sites

Answer 10

Exploit anatomical sites usually shielded from imm syst attention eg kidney (polyoma and cytomegalo), salivary gland (cytomegalo), skin (papilloma), pns and cns (many viruses)

Question 11

Canine distemper birus persistance

Answer 11

An prod rare condition of old dog encephalitis similar to SSPE disease in humans cause by measles
Mech of SSPE persistance is thought to involve a defective viral pro, M pro, key in virus assembly. No new virus is produced in infected neurons but the viral genome is able to spread to neighbouring cells by cell fusion