Influenza A is one of the viruses in circulation that causes what we colloquially call the flu,

though it varies from some other flu-causing pathogens, in that it is primarily relegated to birds.

So the four types of influence of viruses we track, influenza A, B, C, and D, are similar enough

that we can trace them back to the same rough ancestral lineage, and they cause

somewhat similar symptoms in those they infect.

But influenza B and C are primarily human viruses.

D is most commonly found in cattle, like cows and pigs, and influenza A is a primarily

bird-infecting virus.

But these viruses have been known to jump to other species, in some cases just a little, and with very little impact, and in some cases somewhat more enthusiastically, and with fairly worrying, or at times fairly devastating outcomes, though thankfully still in relatively small pockets, even in those worst cases.

There are, theoretically at least,

one hundred ninety-eight different combinations of the proteins that cause variation within the influenza A virus lineage,

though only 18 of those combinations have been seen in the wild and documented.

And these known versions of this virus are named according to their lineage, their deadliness, their subtype, or their typical host.

And some have several names. The subtype moniker may be used within scientific circles, while the host name, which is easier to remember and more informative to the non-science person,

might be used more casually and in the press.

For instance, a strain of the H5N1 influenza A virus is more commonly called the avian influenza,

or avian flu, or just bird flu, if you want to get real casual about it.

There are records of this flu, or something very similar to it, as early as 1878,

but there's some reason to believe it was blended in with several other diseases,

like Newcastle disease and foul plague before then,

and forward in time as late as the mid-20th century,

as we didn't really have a great way of saying for certain what was causing what,

...