Influenza is an
enveloped virus of the family
orthomyxovirus. They have a (-)stranded
segmented RNA genome. It has two
proteins on its surface which are particularly important,
hemagglutinin(HA) and
neuraminidase(NA). NA serves to cleave
mucus, making it less
viscous, and allowing the virus to move to infect the host. HA causes the virus
particle to bind to
cells, and facilitates
endocytosis. Once the virus has been endocytosed, the
pH of the endocytic
vesicle drops, causing the virus to fuse with the
membrane and release its genome into the
cytoplasm.
Typically influenza undergoes a tremendous amount of genetic drift, with common strains changing from year to year, requiring a change in the vaccine. Strains are typically named after the type of HA and NA
surface proteins they have, so a typical name would be something like "influenza H2N7". The normal
reservoirs of the virus are
pigs and
fowl (
chickens,
ducks). Several years ago, over a million chickens were destroyed in
Hong Kong because they were harboring a particularly
virulent influenza strain that probably would have crossed over into humans eventually.