Avian influenza
(also known as bird flu, avian
flu, influenzavirus A flu, type A flu, or genus A flu)
is a flu (influenza) due to a type of influenza virus that is hosted
by birds, but may infect several species of mammals. It was first
identified in Italy in the early 1900s and is now known to exist
worldwide. [1]
The annual flu (also called "seasonal flu" or "human flu") kills an
estimated 36,000 people in the United States each year. The annual
flu vaccine is made by combining vaccines for the new versions of
H1N1 and H3N2 viruses that nature produces each year. The dominant
strain in January 2006 is H3N2. Measured resistance to the standard
antiviral drugs amantadine and rimantadine in H3N2 has increased
from 1% in 1994 to 12% in 2003 to 91% in 2005. "[C]ontemporary human
H3N2 influenza viruses are now endemic in pigs in southern China and
can reassort with avian H5N1 viruses in this intermediate host."
Avian flu is a disease and
avian flu virus is a species. The avian flu virus subtypes are
labeled according to an H number and an N number. (Flu means
influenza.) Each subtype virus has mutated into a variety of strains
with differing pathogenic profiles; some pathogenic to one species
but not others, some pathogenic to multiple species. Most known
strains are extinct strains. For example, the annual flu subtype
H3N2 no longer contains the strain that caused the Hong Kong Flu.
The avian influenzavirus subtypes that have been confirmed in
humans, ordered by the number of known human deaths, are: H1N1
caused Spanish flu, H2N2 caused Asian Flu, H3N2 caused Hong Kong
Flu, H5N1 is the current pandemic threat, H7N7, H9N2, H7N2, H7N3.
Avian influenza viruses compose the Influenzavirus A genus of the
Orthomyxoviridae family and are negative sense, single-stranded,
segmented RNA viruses. "There are 16 different HA antigens (H1 to
H16) and nine different NA antigens (N1 to N9) for influenza A.
Until recently, 15 HA types had been recognized, but a new type
(H16) was isolated from black-headed gulls caught in Sweden and the
Netherlands in 1999 and reported in the literature in 2005."
The World
Health Organization (WHO) has warned of a substantial risk of an
influenza epidemic in the near future, most probably from the H5N1
type of avian influenzavirus. One of the primary concerns is that
the virus could quickly spread across countries as various birds
follow their migration routes. In response, countries have begun
planning in anticipation of an outbreak. While short-term strategies
to deal with an outbreak focus on limiting travel and culling and
vaccinating poultry, long-term strategies require substantial
changes in the lifestyles of the most at-risk populations.