Thursday, July 16, 2009
Scientific Facts About Swine Flu
Swine influenza (also called swine flu, hog flu and pig flu) is an infection of a host animal by any one of several specific types of swine influenza virus. In 2009 the media labeled as "swine flu" flu caused by 2009's new strain of swine-origin A/H1N1 pandemic virus just as it had earlier dubbed as "avian flu" flu caused by the recent Asian-linage HPAI (High Pathogenic Avian Influenza) H5N1 strain that is still endemic in many wild bird species in several countries.
A swine influenza virus (SIV) is any strain of the influenza family of viruses that is usually hosted by (is endemic in) pigs. As of 2009, the known SIV strains are the influenza C virus and the subtypes of the influenza A virus known as H1N1, H1N2, H3N1, H3N2, and H2N3. Swine flu is common throughout pig populations worldwide.
Transmission of swine influenza virus from pigs to humans is not common and does not always cause human influenza, often only resulting in the production of antibodies in the blood. The meat of the animal poses no risk of transmitting the virus when properly cooked. If transmission does cause human influenza, it is called zoonotic swine flu. People who work with pigs, especially people with intense exposures, are at increased risk of catching swine flu. In the mid-20th century, identification of influenza subtypes became possible, which allows accurate diagnosis of transmission to humans. Since then, fifty confirmed transmissions have been recorded. 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. Pigs can also become infected with human influenza, and this appears to have happened during the 1918 flu pandemic.
The 2009 swine flu outbreak in humans is due to a new strain of influenza A virus subtype H1N1 that contains genes closely related to swine influenza. The origin of this new strain is unknown. However, the World Organization for Animal Health (OIE) reports that this strain has not been isolated in pigs. This strain can be transmitted from human to human, and causes the normal symptoms of influenza.
Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Influenzavirus A includes only one species: Influenza A virus which causes influenza in birds and some mammals. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon. Some isolates of influenza A virus cause severe disease both in domestic poultry and, rarely, in humans. Occasionally viruses are transmitted from wild aquatic birds to domestic poultry and this may cause an outbreak or give rise to human influenza pandemics.
Influenza A viruses are negative sense, single-stranded, segmented RNA viruses. There are several subtypes, labeled according to an H number (for the type of hemagglutinin) and an N number (for the type of neuraminidase). There are 16 different H antigens (H1 to H16) and nine different N antigens (N1 to N9). The newest H type (H16) was isolated from black-headed gulls caught in Sweden and the Netherlands in 1999 and reported in the literature in 2005.
Each virus subtype has mutated into a variety of strains with differing pathogenic profiles; some pathogenic to one species but not others, some pathogenic to multiple species.
Influenza A virus subtype H1N2
H1N2 is a subtype of the species Influenza A virus (sometimes called bird flu virus). It is currently pandemic in both human and pig populations.
H1N1, H1N2, and H3N2 are the only known Influenza A virus subtypes currently circulating among humans.
The new A(H1N2) strain appears to have resulted from the reassortment of the genes of the currently circulating influenza A(H1N1) and A(H3N2) subtypes. The hemagglutinin protein of the A(H1N2) virus is similar to that of the currently circulating A(H1N1) viruses and the neuraminidase protein is similar to that of the current A(H3N2) viruses.
It is unknown where the A(H1N2) virus originated, but on February 6, 2002, the World Health Organization (WHO) in Geneva and the Public Health Laboratory Service (PHLS) in the United Kingdom reported the identification influenza A(H1N2) virus from humans in the UK, Israel, and Egypt. In addition to the virus isolates reported by WHO and PHLS, the Centers for Disease Control and Prevention has identified influenza A(H1N2) virus from patient specimens collected during the 2001-2002 and 2002-2003 seasons.* Influenza A(H1N2) viruses have circulated transiently in the past. Between December 1988 and March 1989, 19 influenza A(H1N2) virus isolates were identified in 6 cities in China, but the virus did not spread further.
A(H1N2) was also identified during the 2001-2002 flu season (northern hemisphere) in Canada, the U.S.A., Ireland, Latvia, France, Romania, Oman, India, Malaysia, and Singapore.
The H1N2 virus is not very different from the currently circulating influenza viruses. The H1 protein of the H1N2 virus is like the H1 protein of the currently circulating H1N1 viruses and the N2 protein is similar to the N2 protein in the currently circulating H3N2 viruses. The difference is that we don't commonly see the H1 and N2 proteins on the same virus.
The A(H1N2) virus is not causing a more severe illness than other influenza viruses, and no unusual increases in influenza activity have been associated with the A(H1N2) virus. Because both the hemagglutinin and neuraminidase protein on the A(H1N2) virus closely matches the hemagglutinin and neuraminidase proteins of viruses included in the current influenza vaccine, the vaccine should provide good protection against influenza A(H1N2) virus as well as protection against the currently circulating A(H1N1), A(H3N2), and B viruses.
Influenza A virus subtype H3N1
H3N1 is a subtype of the species Influenza A virus, mostly affecting pigs.
Influenza A virus subtype H3N2
Influenza A virus subtype H3N2 (also H3N2) is a subtype of viruses that cause influenza (flu). H3N2 viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains. H3N2 is increasingly abundant in seasonal influenza, which kills an estimated 36,000 people in the United States each year.
Influenza A virus subtype H2N3
H2N3 is a subtype of the influenza A virus. Its name derives from the forms of the two kinds of proteins on the surface of its coat, hemagglutinin (H) and neuraminidase (N). H2N3 viruses can infect birds and mammals
P.S.: Credit goes to cdc and wikipedia for this information.