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Influenza is a pleomorphic, enveloped, single-stranded
RNA virus of the family Orthomyxoviridae.
There are at four subtypes: Genus Influenzavirus
A, Genus Influenzavirus B, Genus Influenzavirus
C, and Genus "Tthogoto-like Viruses."
Influenza A and B cause epidemics of respiratory
illness in humans and animals. Animal hosts include:
birds, pigs, ducks, whales, horses, and seals.
Variations in the two surface proteins of influenza
A, hemagglutinin (H) and neuraminidase (N), are
used to describe specific viruses. At least 15
types of hemagglutinin and 9 types of neuraminidase
are recognized, although not all forms are seen
in human infections. Significant change in these
proteins is often associated with epidemics. Worldwide
epidemics occur when changes to these
proteins are marked, such as when a form of influenza
A only seen in animals suddenly begins to infect
humans.
Human vaccines against influenza A & B are
annually designed to protect against the threat
of changes in endemic influenza strains.
In recent years, influenza strains normally
only detected in birds (H5N1
and H9N2)
have caused disease in humans. The cross-species
movement of influenza merits close surveillance.
The following web sites contain detailed information
regarding influenza:
All
the Virology on the Web
Centers for Disease Control & Prevention (CDC)
Food and Agricultural Organization (FAO)
National Wildlife Health Center avian influenza
The Big Picture Book of Viruses: Orthomyxoviridae US Dept of Labor protecting poultry workers
US pandemic influenza plan
USDA avian influenza
USDA APHIS avian influenza
US Fish and Wildlife Service
World Organization for Animal Health (OIE) avian influenza
World Health Organization (WHO) avian flu
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