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Pandemic Research
The Basics of Flu
A flu virus is roughly
round, but it can also be elongated or irregularly shaped.
Inside are the genetic instructions for making new copies
of the virus. Flu's most striking feature is a layer of
spikes projecting from its surface. There are two
different types of spikes: one which
allows the virus to "stick" to a cell and initiate
infection, the other is a protein which enables newly
formed viruses to exit the host cell.
Virus A, B, C
Influenza viruses are
classified as type A, B, or C based upon their protein
composition. Type A viruses are found in many kinds of
animals, including ducks, chickens, pigs, whales, and also
in humans. The type B virus widely circulates in humans.
Type C has been found in humans, pigs, and dogs and causes
mild respiratory infections, but does not spark epidemics.
Type A influenza is the most frightening of the three. It
is believed responsible for the global outbreaks of 1918,
1957 and 1968.
Where Influenza Comes
From
In nature, the flu virus is found in wild aquatic birds
such as ducks and shore birds. It has persisted in these
birds for millions of years and does not typically harm
them. But the frequently mutating flu viruses can readily
jump the species barrier from wild birds to domesticated
ducks and then to chickens. From there, the next stop in
the infectious chain is often pigs.
Pigs can be infected by both bird (avian) influenza and
the form of influenza that infects humans. In a setting
such as a farm where chickens, humans and pigs live in
close proximity, pigs act as an influenza virus mixing
bowl. If a pig is infected with avian and human flu
simultaneously, the two types of virus may exchange genes.
Such a mutated flu virus can sometimes spread from
pigs to people.
In 1997, for the first time, scientists found that bird
influenza skipped the pig step and infected humans
directly. Alarmed health officials feared a worldwide
epidemic (a pandemic). But, fortunately, the virus could
not pass between people and thus did not spark an
epidemic. Scientists speculate that chickens may now also
have the receptor used by human-type viruses.
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