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What is swine influenza?
Swine influenza (swine flu) is caused by type A
influenza virus and gives pigs the flu. Swine flu
viruses cause regular outbreaks of flu in pigs but death
is infrequent. The viruses may circulate among pigs
throughout the year, but most outbreaks occur during the
late fall and winter months similar to outbreaks in
humans. The classical swine flu virus (an influenza type
A H1N1 virus) was first isolated from a pig in 1930.
How many swine flu viruses are there?
Like all flu viruses, swine flu viruses change
constantly. Pigs can be infected by avian, human and
swine influenza viruses. When influenza viruses from
different species infect pigs, the viruses can reassort
and new ones emerge that are a mix of swine, human
and/or avian influenza viruses. Over the years,
different variations of swine flu viruses have emerged.
Right now, there are four main influenza type A virus
subtypes that have been isolated in pigs: H1N1, H1N2,
H3N2, and H3N1. However, most of the recently isolated
influenza viruses from pigs have been H1N1 viruses.
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