
Influenza caused by strains of influenza virus called swine influenza virus that usually affect pigs is known as swine flu. In Midwestern United States, Canada, South America, Mexico, Japan, eastern Asian countries, it is found in pigs. Properly cooked pork poses no risk of transmission of swine influenza virus from pig to human. When infected, virus shows the signs of infection in the presence of antibodies and does not always cause human influenza, detectable only by laboratory tests.
It is called zoonotic flu when transmission results in a human influenza. People with intensive exposure to pigs or those who work with pigs are at risk of catching flu. Mal Since the mid twentieth century only 50 such transmissions have been recorded. The strains of swine flu pass from one human to another, and show common symptoms like chills, fever, muscle pains, sore throat, coughing, severe headache, weakness and general discomfort. The 2009 flu outbreak which is also known as the 'swine flu' is caused due to new strain of influenza A virus subtype H1N1. This virus contains genes closely related to swine influenza. Its origin is not known but the world organization for animal health claims that this virus is not isolated to pigs, it can also pass from human to human to cause normal symptoms of influenza.
Out of the genera of influenza virus, influenza virus C is common in pigs and influenza virus A is rare. Humans and pigs are infected due to influenza virus C and not birds. Transmission between human and pigs occurred before: for instance, influenza C caused outbreak of mild among children in Japan, but due to its limited host range and lack of genetic diversity, it did not became pandemic. It is also caused by influenza subtypes like H1N1, H1N2, H3N1, H3N2 and H2N3.
The first case of swine flu was found on 1918, when pigs as well as human became ill at the same time. For the following next 60 years the common strain was H1N1. after that between 1997 and 2003, its different subtypes emerged. With only 12 cases in US since 2005, its direct transmission from pigs to humans is rare. For several times it has been reported as a zoonosis in humans, usually with limited distribution. These outbreaks cause significant losses in industry. The 1918 flu pandemic was related to H1N1 and flu appeared in pigs. In this case, human caught disease from pigs. The exact origin of 1918 outbreak remains unknown. On October 1, 1976 the immunization program began and by the start of November 40 million people are vaccinated. In 1988 one woman was killed due to swine flu in its outbreak. This outbreak proved the fact that pigs can serve as crucible where novel influenza viruses emerge as resentment of genes from different strains. The 2009 outbreak is due to new strain H1N1 which is not previously reported in pigs and it is reported at pigs' farm at Alberta, Canada.




