Influenza Virus

Question 1

what strain are the majority of influenza diseases

Answer 1

influenza A

Question 2

influenza structure

Answer 2

single stranded RNA
enveloped
segmented genome

Question 3

what are the most relevant segments of influenza genome

Answer 3

segment 4 and 6

both are surface proteins required for attachment to host cells

combination of H and N segments determines strain (ex. H1N1)

Question 4

segment 4

Answer 4

H segment; hemagglutinin

binds to a2,3 or a2,6 sialic acid receptors on host epithelial cells

Question 5

segment 6

Answer 5

N segment; neuraminidase - determines antigenicity

NA tethers the new virus to the host cell after replication is complete; cleaves it once host cell is near another sialic acid receptor to facilitate transmission

Question 6

antigenic shift

Answer 6

two different strains infect a host cell at the same time (confection) causing segments from each to recombine during replication and produce a new subtype

causes PANDEMICS because hosts do not have the appropriate immune response to the new subtype

Question 7

antigenic drift

Answer 7

single strain infects a host cell and mutates during replication to produce a new sequence

causes SEASONAL VARIATION within the same subtype

Question 8

why are mutations in viral replication so common

Answer 8

virus polymerases are unable to correct mutations, making them very error prone

viruses only use host ribosomes NOT host polymerases (which are able to correct mutations)

Question 9

what receptors do influenza viruses bind to

Answer 9

sialic acid receptors

distribution of receptors determines virus tropism for certain hosts and tissues

Question 10

avian influenza receptors

Answer 10

a2,3 SA receptors located in the GUT

causes GI disease and shedding in the feces

does NOT cause disease in wild birds

DOES cause disease in domestic ducks and poultry

Question 11

mammalian influenza receptors

Answer 11

a2,6 SA receptors located in the RESPIRATORY TRACT

causes respiratory disease and shedding in saliva or airborne particles

Question 12

pig influenza receptors

Answer 12

BOTH 2,3 and 2,6 SA receptors in the RESPIRATORY TRACT

pigs are able to get infected by both avian and mammalian strains of influenza –> “mixing vessels” for influenza

Question 13

pathogenesis of influenza

Answer 13

1. viral envelope attaches to cell membrane
2. fuses and uncoats inside cell
3. replication and cytokine/granzyme production
4. causes airway and alveolar inflammation
5. inflammation damages airway cells leading to hyper-reactivity + constriction
6. outcome: bronchial asthma and COPD

Question 14

zoonotic influenza

Answer 14

viruses transmitted from animals to humans

does NOT have human to human transmission

ex. H5N1 bird flu

Question 15

pandemic influenza

Answer 15

global human to human spread of NOVEL viruses derived from antigenic SHIFT

new H#N# subtype emerges that has not circulated RECENTLY in people and causes disease in humans
- easily transmitted due to lack of immune memory to that subtype
- can get repeated subtypes if it has been long enough between pandemics
ex. 1977 H1N1 vs 2009 H1N1

Question 16

seasonal influenza

Answer 16

regular, yearly transmission of human-adapted viruses that have antigenically DRIFTED from previous year
- SAME H#N# subtype but mutated sequence

variants of previous pandemic viruses
- after a new subtype evolved - seasonal strains follow for years after

Question 17

what are the most common seasonal flu strains

Answer 17

H1N1 and H3N2

occurs between October and May

Question 18

influenza reservoir

Answer 18

wild birds
- non-pathogenically infected

Question 19

influenza transmission

Answer 19

1. direct transmission from wild birds to:
   - marine mammals
   - domestic ducks
   - bats
   - cats +/- dogs
2. indirect transmission via domestic ducks to:
   - poultry
   - pigs
   - horses
3. pigs act as “mixing vessels” to infect:
   - humans
   - dogs
   - horses

Question 20

prevention of influenza spread

Answer 20

from ducks –> poultry, pigs, horses:
- water treatment
- biosecurity
- indoor raising

from pigs:
- “stamping out”
- quarantine
- decontamination
- movement restriction

to humans, dogs, horses:
- vaccines
- market hygiene
- live market closure

Question 21

avian influenza strain

Answer 21

H1N1
- reportable
- high and low pathogenic strains (both cause fatality)
- no vaccine available
- can spread H5N1 to humans

Question 22

equine influenza strain

Answer 22

H3N8
- spread from birds –> horses
- high morbidity: respiratory infection
- low mortality
- self limiting

Question 23

canine influenza strains

Answer 23

H3N8: spread from horses; not clinically relevant

H3N2: spread from birds; causes mild upper respiratory disease
- cough, lethargy, sneezing, ocular discharge
- self-limiting

Question 24

marine influenza strain

Answer 24

H3N8
- spread from birds to seals
- seals can act as mixing vessels for avian and mammalian strains

Question 25

CIV vaccine

Answer 25

non core
at risk animals only

Question 26

EIV vaccine

Answer 26

non core
at risk animals only

Question 27

avian influenza vaccine

Answer 27

NONE available
- long production time
- poor efficacy

Question 28

human influenza vaccine

Answer 28

vaccines updated yearly based on forecasting upcoming flu strains
- combines circulating strain with master high growth strain
- recombinant: selects for high growth properties of the master strain + antigenicity of the circulating strain
- inactivated
- quadrivalent - makes a prediction of what 4 strains to include based on current circulating strains

Question 29

influenza diagnostics

Answer 29

1. PCR
2. rapid antigen
3. viral culture