Swine flu
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Swine Flu (or Swine influenzavirus (SIV) flu) refers to a subset of Orthomyxoviridae that creates influenza in pigs and are endemic in pigs. This is not a phylogenetics based taxonomic category.
The species of Orthomyxoviridae that can cause flu in pigs are Influenza A virus and Influenza C virus but not all genotypes of these two species infect pigs.[1]
The known subtypes of Influenza A virus that create influenza in pigs and are endemic in pigs are H1N1, H1N2, H3N1 and H3N2. [2] [3]
"In swine, 3 influenza A virus subtypes (H1N1, H3N2, and H1N2) are circulating throughout the world. In the United States, the classic H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. Most H3N2 virus isolates are triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages. [...] Present vaccination strategies for SIV control and prevention in swine farms typically include the use of 1 of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 isolates had strong serologic cross-reactions with antiserum to 3 commercial SIV vaccines. Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus, the presence of nonreactive H3N2 SIV variants suggests that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses."[4]
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[edit] H5N1
Avian influenza virus H3N2 is endemic in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. Health experts say pigs can carry human influenza viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment) with H5N1, passing genes and mutating into a form which can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift and caused the Hong Kong Flu pandemic of 1968 and 1969 that killed up to 750,000 humans. The dominant strain of annual flu in humans in January 2006 is H3N2. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 in humans has increased to 91% in 2005. A combination of these two subtypes of the species known as the avian influenza virus in a country like China is a worst case scenario. In August 2004, researchers in China found H5N1 in pigs.[5]
In 2005 it was discovered that H5N1 "could be infecting up to half of the pig population in some areas of Indonesia, but without causing symptoms [...] Chairul Nidom, a virologist at Airlangga University's tropical disease center in Surabaya, Java, [Indonesia] was conducting independent research earlier this year. He tested the blood of 10 apparently healthy pigs housed near poultry farms in western Java where avian flu had broken out, Nature reported. Five of the pig samples contained the H5N1 virus. The Indonesian government has since found similar results in the same region, Nature reported. Additional tests of 150 pigs outside the area were negative."[6]
[edit] Veterinary swine flu vaccine
Swine influenza has become a greater problem in recent decades. Evolution of the virus has resulted in inconsistent responses to traditional vaccines. Standard commercial swine flu vaccines are effective in controlling the problem when the virus strains match enough to have significant cross-protection and custom (autogenous) vaccines made from the specific viruses isolated are created and used in the more difficult cases.[7] SIV vaccine manufacture Novartis paints this picture: "A strain of swine influenza virus (SIV) called H3N2, first identified in the US in 1998, has brought exasperating production losses to swine producers. Abortion storms are a common sign. Sows go off feed for two or three days and run a fever up to 106°F. Mortality in a naïve herd can run as high as 15%."[8]
[edit] The U.S. swine flu scare of 1976
On February 5, 1976, an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that swine flu was the cause of death and that this strain of flu appeared to be closely related to the strain involved in the 1918 flu pandemic. Alarmed public-health officials decided that action must be taken to head off another major pandemic, and they urged that every person in the U.S. be vaccinated for the disease. President Gerald Ford was confronted with a potential swine flu pandemic. The vaccination program was plagued by delays and public relations problems, but about 24% of the population was vaccinated by the time the program was cancelled. [9]
An immunopathological reaction to the vaccine in some people is believed to have caused about 500 cases of Guillain-Barré syndrome resulting in death from severe pulmonary complications for 25 people. More people died from the vaccine than died from the swine flu itself.[9] Other influenza vaccines have not been clearly linked to Guillain-Barré syndrome.[10]
[edit] The Philippine swine flu outbreak of 2007
On August 20, 2007, Department of Agriculture officers investigated the outbreak of swine flu in Nueva Ecija and Central Luzon, Philippines. The mortality rate is less than 10 % for swine flu, if there are no complications like hog cholera. Earlier, or on July 27, 2007, the Philippine National Meat Inspection Service (NMIS) raised a hog cholera "red alert" warning over Metro Manila and 5 regions of Luzon after the disease spread to backyard pig farms in Bulacan and Pampanga, even if these tested negative for the swine flu virus.[11][12]
[edit] See also
[edit] Sources
- ^ Veterinary Sciences Tomorrow article Swine influenza: a zoonosis by Paul Heinen dated 15 September 2003 says "Influenza B and C viruses are almost exclusively isolated from man, although influenza C virus has also been isolated from pigs and influenza B has recently been isolated from seals."
- ^ Swine Diseases (Chest) - Swine Influenza, Iowa State University College of Veterinary Medicine
- ^ eurekalert Tips from the Journals of the American Society for Microbiology - Novel H3N1 Swine Influenza Virus Identified in Pigs in Korea
- ^ pubmedcentral.nih.gov Canadian Journal of Veterinary Research (2007 July; 71(3): 201–206.) article Serologic and genetic characterization of North American H3N2 swine influenza A viruses by Marie René Gramer, Jee Hoon Lee, Young Ki Choi, Sagar M. Goyal, and Han Soo Joo
- ^ WHO (October 28, 2005). H5N1 avian influenza: timeline.
- ^ CIDRAP article Indonesian pigs have avian flu virus; bird cases double in China published May 27, 2005
- ^ National Hog Farmer article Swine Flu Virus Turns Endemic published September 15, 2007
- ^ livestock.novartis.com Custom Vaccines: Swine
- ^ a b The Sky is Falling: An Analysis of the Swine Flu Affair of 1976
- ^ University of Illinois at Springfield
- ^ GMA NEWS.TV, DA probes reported swine flu 'outbreak' in N. Ecija
- ^ GMA NEWS.TV, Gov't declares hog cholera alert in Luzon
[edit] Further reading
- The Swine Flu Episode and the Fog of Epidemics by Richard Krause in CDC's Emerging Infectious Diseases Journal Vol. 12, No. 1 January 2006 published December 20, 2005
- SWINE INFLUENZA by Carol G. Woodlief of College of Veterinary Medicine at North Carolina State University Overview, symptoms in pigs, treatment for pigs
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