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Swine influenza (also called swine flu, hog flu, and pig flu) refers to influenza caused by those strains of influenza virus that usually infect pigs and are called swine influenza virus (SIV).[1] Swine influenza is common in pigs in the midwestern United States (and occasionally in other states), Mexico, Canada, South America, Europe (including the United Kingdom, Sweden, and Italy), Kenya, Mainland China, Taiwan, Japan and other parts of eastern Asia.[1]
Transmission of swine influenza virus from pigs to humans is not common. When it is transmitted, it does not always cause human influenza; often, the only sign of infection is the presence of antibodies, detectable only by laboratory tests. When transmission results in influenza in a human, it is called zoonotic swine flu. People who work with pigs, especially people with intense exposures, are at risk of catching swine flu. However, only about fifty such transmissions have been recorded since the mid-20th Century, when identification of influenza subtypes became possible. (Importantly, eating pork does not pose a risk of infection.) Rarely, these strains of swine flu can pass 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" is due to an apparently virulent new strain of influenza A virus subtype H1N1 that was produced by reassortment from one strain of human influenza virus, one strain of avian influenza virus, and two separate strains of swine influenza. The origin of this new strain is unknown, and the World Organization for Animal Health (OIE) reports that this strain has not been isolated in pigs.[2] It passes with apparent ease from human to human, an ability attributed to an as-yet unidentified mutation.[3] This 2009 H1N1 strain causes the normal symptoms of influenza, such as fever, coughing and headache.[4]
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