Influenza Virus Flashcards
what strain are the majority of influenza diseases
influenza A
influenza structure
single stranded RNA
enveloped
segmented genome
what are the most relevant segments of influenza genome
segment 4 and 6
both are surface proteins required for attachment to host cells
combination of H and N segments determines strain (ex. H1N1)
segment 4
H segment; hemagglutinin
binds to a2,3 or a2,6 sialic acid receptors on host epithelial cells
segment 6
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
antigenic shift
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
antigenic drift
single strain infects a host cell and mutates during replication to produce a new sequence
causes SEASONAL VARIATION within the same subtype
why are mutations in viral replication so common
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)
what receptors do influenza viruses bind to
sialic acid receptors
distribution of receptors determines virus tropism for certain hosts and tissues
avian influenza receptors
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
mammalian influenza receptors
a2,6 SA receptors located in the RESPIRATORY TRACT
causes respiratory disease and shedding in saliva or airborne particles
pig influenza receptors
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
pathogenesis of influenza
- viral envelope attaches to cell membrane
- fuses and uncoats inside cell
- replication and cytokine/granzyme production
- causes airway and alveolar inflammation
- inflammation damages airway cells leading to hyper-reactivity + constriction
- outcome: bronchial asthma and COPD
zoonotic influenza
viruses transmitted from animals to humans
does NOT have human to human transmission
ex. H5N1 bird flu
pandemic influenza
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
seasonal influenza
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
what are the most common seasonal flu strains
H1N1 and H3N2
occurs between October and May
influenza reservoir
wild birds
- non-pathogenically infected
influenza transmission
- direct transmission from wild birds to:
- marine mammals
- domestic ducks
- bats
- cats +/- dogs - indirect transmission via domestic ducks to:
- poultry
- pigs
- horses - pigs act as “mixing vessels” to infect:
- humans
- dogs
- horses
prevention of influenza spread
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
avian influenza strain
H1N1
- reportable
- high and low pathogenic strains (both cause fatality)
- no vaccine available
- can spread H5N1 to humans
equine influenza strain
H3N8
- spread from birds –> horses
- high morbidity: respiratory infection
- low mortality
- self limiting
canine influenza strains
H3N8: spread from horses; not clinically relevant
H3N2: spread from birds; causes mild upper respiratory disease
- cough, lethargy, sneezing, ocular discharge
- self-limiting
marine influenza strain
H3N8
- spread from birds to seals
- seals can act as mixing vessels for avian and mammalian strains
CIV vaccine
non core
at risk animals only
EIV vaccine
non core
at risk animals only
avian influenza vaccine
NONE available
- long production time
- poor efficacy
human influenza vaccine
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
influenza diagnostics
- PCR
- rapid antigen
- viral culture
