What is it?
Swine influenza virus (referred to as SIV) refers to influenza cases that are caused by Orthomyxoviruses endemic to pig populations. SIV strains isolated to date have been classified either as Influenzavirus C or one of the various subtypes of the genus Influenzavirus A.
Swine flu infects people every year and is found typically in people who have been in contact with pigs, although there have been cases of person-to-person transmission. Symptoms include fever, disorientation, stiffness of the joints, vomiting, and loss of consciousness ending in death. Swine influenza is known to be caused by influenza A subtypes H1N1, H1N2, H3N1, H3N2, and H2N3.
In swine, three influenza A virus subtypes (H1N1, H3N2, and H1N2) are circulating throughout the world.[citation needed] In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.
The 2009 Swine Flu Outbreak
In March and April 2009, more than 1,000 cases of swine flu in humans were detected in Mexico, and more than 80 deaths are suspected to have a connection with the virus. As of April 25, 2009 19:30 EDT there are 11 laboratory confirmed cases in the southwestern United States and in Kansas, and several suspected cases in the New York City metropolitan area. Following a series of reports of isolated cases of swine flu, the first announcement of the outbreak in Mexico was documented on April 23, 2009. Some of the cases have been confirmed by the World Health Organization to be due to a new genetic strain of H1N1. The new strain has been confirmed in 16 of the deaths and 44 others are being tested as of April 24, 2009. The Mexican fatalities are said to be mainly young adults, a hallmark of pandemic flu.
At 8 p.m. on Sunday, April 26, the New Zealand Minister of Health confirmed that 22 students returning from a school trip from Mexico had flu-like symptoms (most likely swine flu). 13 of the students with flu-like symptoms were tested and 10 tested positive for Influenza A, their cases strongly suspected to be the swine flu strain. However there is a possibility that the infected are not infected with the swine flu but other forms of the flu. The government has suggested that citizens of New Zealand with flu-like symptoms should see their physician immediately.
There have been five cases of possible swine flu in Canada, according to the Canadian Press. Two are in British Columbia, and three in Nova Scotia. According to the provincial government, four students in Windsor, Nova Scotia have confirmed cases of swine flu.
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.
On April 26, 2009, some schools in the United States announced closures and cancellations related to possibilities that students may have been exposed to swine flu.
According to University of Virginia virologist Frederick Hayden, the most recent flu season was dominated by H1N1 viruses, and people who had received flu shots in the U.S. may have some protection against swine flu.
