What is the Swine Flu?

Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza that regularly cause outbreaks of influenza among pigs. Swine flu viruses do not normally infect humans, however, human infections with swine flu do occur, and cases of human-to-human spread of swine flu viruses has been documented.

In March and April 2009, more than 1,000 cases of swine flu in humans were detected in Mexico, the southwestern United States, New York City metropolitan area, and two in Kansas, causing more than 80 deaths in Mexico.^[18] Following a series of reports of isolated cases of swine flu,^[19][20] the first announcement of the outbreak in Mexico was documented on April 23. Some of the cases have been confirmed by the World Health Organization to be due to a new genetic strain of H1N1.^[21][22] The new strain has been confirmed in 16 of the deaths and 44 others are being tested as of 24 April 2009.^[23] The Mexican fatalities are mainly young adults, a hallmark of pandemic flu.^[24]

The current vaccine against the seasonal influenza strain H1N1 is thought unlikely to provide protection.^[25] Anne Schuchat, director of CDC's National Center for Immunization and Respiratory Diseases, said that the United States cases were found to be made up of genetic elements from four different flu viruses—North American swine influenza, North American avian influenza, human influenza A virus subtype H1N1, and swine influenza virus typically found in Asia and Europe. For two cases a complete genome sequence had been obtained. She said that the virus was resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).^[26][27][28]

The new strain appears to be a recombinant between two older strains. Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. Viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, but there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S.^[29]