Swine influenza

Classification

Of the three types of influenza viruses that cause human influenza, both also cause flu in pigs, with the influenza virus A are common in pigs and influenza C are rare. Influenza B has not been reported in pigs. In the influenza virus A and C influenza virus, the strains found in pigs and humans are essentially separate, but because of reassortment, there were transfers of genes between strains of passage porcine, avian flu and the limits of the human species.

 Influenza C

Influenza C viruses infect humans and pigs, but does not infect birds. Transmission between pigs and humans have occurred in the past. For example, influenza C caused small outbreaks of a mild form of influenza in children in Japan and California. Thanks to its limited host range and lack of genetic diversity in influenza C, this form of flu does not cause pandemics in humans.

 Influenza A

Swine influenza is known to be caused by influenza A subtypes H1N1, H1N2, H3N1, H3N2 and H2N3. In pigs, three subtypes of influenza A viruses (H1N1, H3N2 and H1N2) strains are most common in the world. In the United States, the H1N1 subtype was exclusively prevalent among populations of swine before 1998, but since late August 1998, subtype H3N2 were isolated from pigs. In 2004 isolates of H3N2 viruses in pigs and the United States were turkey stocks triple reassortant containing genes from human (HA, NA and PB1), swine (NS, NP, and M), and of avian (PB2 and PA) lineages.

Surveillance

Although there is no national surveillance system of the United States to determine the circulating viruses in pigs, it is a monitoring network of the United States which is part of a global monitoring network.

Veterinary pathologist, Tracey McNamara, established a national system of disease surveillance in zoos because zoos do active surveillance of diseases and many exotic animals housed large susceptibilities. Many species below the radar of a fall federal agencies (including dogs, cats, pet prairie dogs, zoo animals, wildlife and urban), although in May be important in early detection of outbreaks of human diseases.
 

History

The swine flu was first proposed to a disease related to human influenza during the influenza pandemic of 1918, when pigs became sick at the same time as humans. The first identification of a flu virus as a cause of disease in pigs occurred a decade later, in 1930. For 60 years, the swine influenza were almost exclusively of H1N1 strains. Then, between 1997 and 2002, new strains of three and five subtypes genotypes appeared that cases of influenza in pigs in North America. In 1997-1998, the H3N2 strains appeared. These strains, which include derivatives of reassortment of genes humans, pigs and avian viruses have become a major cause of swine influenza in North America. Reassortment   between H1N1 and H3N2 product H1N2. In 1999 in Canada, a strain of H4N6 has crossed the species barrier from birds to pigs, but was contained on a single farm.