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Cards In This Set
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Who does type A avian influenza affect?
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Most mammals and aves. humans, dogs, horses, whales, seals, tigers, swine, etc.
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Human Seasonal Influenza
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There are a few types of avian influenza circulating and they can present themselves as seasonal influenza viruses.
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Type C influenza
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It causes milder infections and is associated with sporadic cases and minor localizard outbreaks. Not that big a deal.
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Which influenza type is avian influenza caused by?
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Influenza A virus
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What are the 2 avian influeza pathotypes? Describe them.
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HPAI (High pathogenicity) and LPAI (Low pathogenicity). The HPAI is a severe, systemic disease whereas the LPAI mainly attacks the respiratory and reprodctive tracts.
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What are clinical signs of AI?
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They can range from mild to asymptomic to a fatal disease. In HPAI, there is high death losses, severe depression, sudden drop in production of eggs, swollen wattles and hemorrhages of legs.
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What are AI virus genome characteristics?
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It has 8 genetic segments of linear negative-sense ss RNA
there are many subtypes. - H (1-16 or 18) - N (1-10) virion is pleomorphic. |
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Explain importance of HA cleavage.
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The HA cleavage is when the endosomal pH reaches 5.0 and the HA protein undergoes a conformational rearrangement. this change exposes a fusion peptide on the HA- a short, hydrophobic sequence that inserts intot he endosomal membrane and causes it to fuse with the viral envelope. then viral RNAs are released into host cell cytoplasm.
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How do cleavage of LPAI and HPAI HA proteins differ
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In LPAI viruses, only trypsin-like proteases found in the enteric (intestines) and respiratory tracts can cleave the HA protein. the disease is restricted because virus replication is restricted. however, in HPAI viruses, the HA protein can be cleaved by many different proteases found in most cells. thus, the viruses can replicate systemically and is not restricted.
so they both start with HA0 and it gets cleaved into either HA1 or HA2 |
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How do you know if HA0 becomes HA1 or HA2?
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The link b/w HA1 and HA2 is the structure of the uncleaved precursor and how it interacts with the proteases. for LPAIs, the cleavage site usually consists of single arginine whereas HPAIs have multiple basic amino residues so the cleavage site has a R-X-K/R-R sequence
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Sialic acid receptors
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These receptors determine which host the virus will bind to. AIV HA binds to 2-3 sialic avid receptors on host cells. HumanIV HA binds a 2-6 sialic avid receptors. swine influenza viruses have the ability to bind to both AIV and HumanIV sialic acid receptors.
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How do you name an influenza virus?
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Virus type/geographic origin/strain number/year of isolation/virus subtype
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Antigenic drift (minor)
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Antigenic drift occurs from point mutations in the HA or NA genes that results in minor antigenic changes in those proteins
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Antigenic shift (major)
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Antigenic shift occurs during coinfectionand genetic reassortment when gene segments interchange
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 Describe the image in terms of antigenic drift and antigenic shift. |
Antigenic shift is more serious than antigenic drift. Antigenic shift is the genetic reassortment of the gene segments during a coinfection. A human and a bird have different strains of AI, then they coinfect a pig and the pig in turn gives a product of both strains of AI. Whereas, antigenic drift results from point mutations in the HA or NA genes in an organism.
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