Flu, Bird Flu, Influenza A virus subtype
H5N1, also known as A(H5N1) or H5N1. Avian flu
is any flu caused by a virus adapted to birds. (Also
called "bird flu", "avian influenza"
and "bird influenza".)
The only known such viruses are Influenza
A viruses. Most people use "avian flu" to
mean H5N1 which is the subtype of the species Influenza
A virus that is a current pandemic threat.
Avian flu viruses are noninfectious
for most species. When they are infectious they are
usually asymptomatic, so the carrier does not have any
disease from it.
Thus while infected with an avian
flu virus, the animal doesn't have a "flu".
Typically, when illness (called "flu") from
an avian flu virus does occur, it is the result of an
avian flu virus strain adapted to one species spreading
to another species (usually from one bird species to
another bird species).
So far as we know the most common
result of this is an illness so minor as to be not worth
noticing (and thus little studied). But with the domestication
of chickens and turkeys, we have created species subtypes
(domesticated poultry) that can catch an avian flu virus
adapted to waterfowl and have it rapidly mutate into
a form that kills in days over 90% of an entire flock
and spread to other flocks and kill 90% of them and
can only be stopped by killing every domestic bird in
Until H5N1, this was basically the
whole story of avian flu so far as anyone knew or cared
(outside of the poultry industry). Now with H5N1, we
have a whole new ballgame with H5N1 inventing new rules
as it goes with behaviors never noticed before, and
possibly never having occurred before.