Swine Flu

Swine influenza (also swine flu, hog flu,[1] and pig flu[1]) refers to influenza caused by any strain of the influenza virus endemic in pigs (swine). Strains endemic in swine are called swine influenza virus (SIV).[1]

Of the three genera of human flu, two are endemic also in swine: Influenzavirus A is common and Influenzavirus C is rare.[2] Influenzavirus B has not been reported in swine. Within Influenzavirus A and Influenzavirus C, the strains endemic to swine and humans are largely distinct.

Swine flu is common in swine in the midwestern United States (and occasionally in other states), Mexico, Canada, South America, Europe (including the United Kingdom, Sweden, and Italy), Kenya, China, Japan, Taiwan, and other parts of eastern Asia.[1]

Swine flu is rare in humans. People who work with swine, especially people with intense exposures, are at risk of catching swine influenza if the swine carry a strain able to infect humans. However, these strains infrequently circulate between humans as SIV rarely mutates into a form able to pass easily from human to human. In humans, the symptoms of swine flu are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort.

The 2009 flu outbreak in humans that is widely known as "swine flu" apparently is not due to a swine influenza virus. It is due to a new strain of influenza A virus subtype H1N1 that derives from one strain of human influenza virus, one strain of avian influenza virus, and two separate strains of swine influenza virus. The origins of this new strain are unknown, and the World Organization for Animal Health (OIE) reports that this strain has not been isolated in swine.[3]

It passes with apparent ease from human to human, an ability attributed to an as-yet unidentified mutation.[4] The strain in most cases causes only mild symptoms and the infected person makes a full recovery without requiring medical attention and without the use of antiviral medicines.[5]