http://www4.eurekalert.org/pub_releases/2005-10/tifg-fbi100305.php
discusses work done at TIGR on influenza.
http://www.scienceinafrica.co.za/2002/june/flu.htm
reveals that: "There are three types of influenza virus, A, B and C.
Types A and B viruses cause epidemics of disease almost every winter,
while type C viruses only cause a mild respiratory illness and are not
considered clinically important. Influenza type A viruses are divided
into subtypes based on two proteins on the surface of the virus, the
haemagglutinin (HA) and neuraminidase (NA). The current subtypes of
influenza A viruses that infect humans are A (H1N1) and A (H3N2).
Influenza A viruses are found in many different animals, including
birds, pigs, horses, whales and seals. Wild aquatic birds are the
reservoir for all subtypes of influenza A viruses. There are fifteen
different haemagglutinin and nine different neuraminidase types that
occur in influenza A viruses in wild birds. Unlike influenza A viruses,
influenza B viruses are not divided into subtypes and have only been
isolated from humans and recently from seals."
And here's why it represents macroevolution that transcends the "kind"
barrier: "Influenza viruses can change in two different ways. The first
way is referred to as "antigenic drift" and occurs by continuous
mutations taking place during the replication cycle of the virus. These
changes are unpredictable and if they occur within the five defined
antigenic sites on the HA protein, can give rise to an antigenically
novel virus. The new variant virus can escape the host's previously
acquired immunity, and can then spread rapidly through a susceptible
population.
"The second type of change, "antigenic shift", occurs in influenza
A viruses. Antigenic shift is an abrupt, major change due to gene
reassortment and results in an influenza A virus with new
haemagglutinin and/or neuraminidase proteins. When a new subtype of
virus appears after antigenic shift that can cause both illness in
humans and can also spread easily from person to person, an influenza
pandemic (worldwide epidemic) can occur. During the last century three
influenza pandemics occurred. In 1918 -1919, the "Spanish flu" caused
approximately 40 million deaths worldwide. The virus that caused it ,
influenza A (H1N1), was unique because almost half of the people who
died were young, healthy adults. The next pandemic, the "Asian flu"
occurred during 1957- 1958 and was the result of an antigenic shift
producing an H2N2 virus. In 1968, a new subtype (H3N2) emerged and was
referred to as the "Hong Kong flu" since it was first detected in Hong
Kong before it spread globally causing the third pandemic."
Budikka
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