Influenza A virus subtype H1N1
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Influenza A virus subtype H1N1, also known as A(H1N1), is a subtype of influenzavirus A and the most common cause of influenza (flu) in humans. Some strains of H1N1 are endemic in humans, including the strain(s) responsible for the 1918 flu pandemic which killed 50–100 million people worldwide. Less virulent H1N1 strains still exist in the wild today, worldwide, causing a small fraction of all influenza-like illness and a large fraction of all seasonal influenza. H1N1 strains caused roughly half of all flu infections in 2006.[1] Other strains of H1N1 are endemic in pigs and in birds.
In March and April 2009, hundreds of laboratory-confirmed infections and a number of deaths were caused by an outbreak of a new strain of H1N1.[2]
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Nomenclature
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Influenza A virus strains are categorized according to two proteins found on the surface of the virus: hemagglutinin (H) and neuraminidase (N). All influenza A viruses contain hemagglutinin and neuraminidase, but the structure of these proteins differs from strain to strain due to rapid genetic mutation in the viral genome.
Influenza A virus strains are assigned an H number and an N number based on which forms of these two proteins the strain contains. There are 16 H and 9 N subtypes known in birds, but only H 1, 2 and 3, and N 1 and 2 are commonly found in humans.[4]
Spanish flu
The Spanish flu, also known as La Gripe Española, or La Pesadilla, was an unusually severe and deadly strain of avian influenza, a viral infectious disease, that killed some 50 million to 100 million people worldwide over about a year in 1918 and 1919. It is thought to be one of the most deadly pandemics in human history. It was caused by the H1N1 type of influenza virus.[5]
The Spanish flu caused an unusual number of deaths because it may have caused a cytokine storm in the body.[6][7] (The recent epidemic of bird flu, also an Influenza A virus, had a similar effect.)[8] The Spanish flu virus infected lung cells, leading to overstimulation of the immune system via release of cytokines into the lung tissue. This leads to extensive leukocyte migration towards the lungs, causing destruction of lung tissue and secretion of liquid into the organ. This makes it difficult for the patient to breathe. In contrast to other pandemics, which mostly kill the old and the very young, the 1918 pandemic killed unusual numbers of young adults, which may have been due to their healthy immune systems being able to mount a very strong and damaging response to the infection.[3]
The term "Spanish" flu was coined because Spain was at the time the only European country where the press were printing reports of the outbreak, which had killed thousands in the armies fighting the First World War. Other countries suppressed the news in order to protect morale.[9]
Russian flu
- See Influenza A virus subtype H2N2#Russian flu for the 1889–1890 Russian flu
The more recent Russian flu was a 1977–1978 flu epidemic caused by strain Influenza A/USSR/90/77 (H1N1). It infected mostly children and young adults under 23 because a similar strain was prevalent in 1947–57, causing most adults to have substantial immunity. Some have called it a flu pandemic but because it only affected the young it is not considered a true pandemic. The virus was included in the 1978–1979 influenza vaccine.[10][11][12][13]
North American flu
Minor outbreaks of swine influenza occurred in humans in 1976 and 1988, and in pigs in 1998 and 2007.
In the 2009 swine flu outbreak, the virus isolated from patients in the United States was found to be made up of genetic elements from four different flu viruses – North American Mexican influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe – "an unusually mongrelised mix of genetic sequences."[14] This new strain appears to be a result of reassortment of human influenza and swine influenza viruses, in all four different strains of subtype H1N1. However, as the virus has not yet been isolated in animals to date and also for historical naming reasons, the World Organisation for Animal Health (OIE) suggests it be called "North-American influenza".[15] On April 30, 2009 the World Health Organization began referring to the outbreak as "Influenza A" instead of "swine flu".[16], and later began referring to it as "Influenza A(H1N1)". Several complete genome sequences for U.S. flu cases were rapidly made available through the Global Initiative on Sharing Avian Influenza Data (GISAID).[17][18] 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. The six genes from American swine flu are themselves mixtures of swine flu, bird flu, and human flu viruses.[19][20] While viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S.[21]
See also
Notes
- ^ "CDC". http://www.cdc.gov/flu/weekly/.
- ^ "Swine influenza - update 3". World Health Organization. http://www.who.int/csr/don/2009_04_27/en/index.html.
- ^ a b Palese P (December 2004). "Influenza: old and new threats". Nat. Med. 10 (12 Suppl): S82–7. doi:. PMID 15577936.
- ^ Lynch JP, Walsh EE (April 2007). "Influenza: evolving strategies in treatment and prevention". Semin Respir Crit Care Med 28 (2): 144–58. doi:. PMID 17458769.
- ^ http://www.fas.org/programs/ssp/bio/factsheets/H1N1factsheet.html
- ^ Kobasa D, Jones SM, Shinya K, et al (January 2007). "Aberrant innate immune response in lethal infection of macaques with the 1918 influenza virus". Nature 445 (7125): 319–23. doi:. PMID 17230189.
- ^ Kash JC, Tumpey TM, Proll SC, et al (October 2006). "Genomic analysis of increased host immune and cell death responses induced by 1918 influenza virus". Nature 443 (7111): 578–81. doi:. PMID 17006449. PMC: 2615558. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=17006449.
- ^ Cheung CY, Poon LL, Lau AS, et al (December 2002). "Induction of proinflammatory cytokines in human macrophages by influenza A (H5N1) viruses: a mechanism for the unusual severity of human disease?". Lancet 360 (9348): 1831–7. PMID 12480361.
- ^ Barry, John M. (2004). The Great Influenza: The Epic Story of the Greatest Plague in History. Viking Penguin. ISBN 0-670-89473-7.
- ^ CNN interactive health timeline box 1977: Russian flu scare
- ^ Time magazine article Invasion from the Steppes published February 20, 1978
- ^ Global Security article Pandemic Influenza subsection Recent Pandemic Flu Scares
- ^ State of Alaska Epidemiology Bulletin Bulletin No. 9 - April 21, 1978 - Russian flu confirmed in Alaska
- ^ "Deadly new flu virus in US and Mexico may go pandemic". New Scientist. 2009-04-26. http://www.newscientist.com/article/dn17025-deadly-new-flu-virus-in-us-and-mexico-may-go-pandemic.html. Retrieved on 2009-04-26.
- ^ A/H1N1 influenza like human illness in Mexico and the USA : OIE statement
- ^ : Renaming of strain to Influenza A(H1N1)
- ^ "Likely Swine Flu In Auckland New Zealand Students". 2009-04-26. http://www.recombinomics.com/News/04260901/H1N1_Swine_Aukland.html.
- ^ "GISAID". http://platform.gisaid.org/dante-cms/live/struktur.jdante?aid=1131.. GISAID is freely available, but subject to license terms and currently subject to a backlog of applications following the outbreak. Some discussion of sequence homologies can be found at "FluTracker.com". http://www.flutrackers.com/forum/showthread.php?t=100610.. The first strains released are A/California/09/2009 7M 2009-04-15, A/Texas/05/2009 16M 2009-04-15, A/Texas/04/2009 16M 2009-04-14, A/California/07/2009 54M 2009-04-09, A/California/06/2009 41F 2009-04-16, A/California/05/2009 9F 2009-03-30, and A/California/04/2009 10M 2009-04-01.
- ^ Susan Watts (2009-04-25). "Experts concerned about potential flu pandemic". BBC. http://www.bbc.co.uk/blogs/newsnight/susanwatts/2009/04/experts_concerned_about_potent.html.
- ^ Dr. Henry Niman at FluTrackers has described the homologies of the genes as PB2 Avian North America, PB1 Human circa 1993, PA Swine Eurasia and/or North America, HA Swine North America, NP Swine Eurasia and/or North America, NA Swine Eurasia, MP Swine Eurasia, NS Swine Eurasia and/or North America.[1]
- ^ "Swine Influenza A (H1N1) Infection in Two Children --- Southern California, March--April 2009". CDC MMWR. 2009-04-22. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5815a5.htm.
External links
- BioHealthBase Bioinformatics Resource Center Database of influenza genomic sequences and related information.
- Outbreak Alerts United States based communicable disease notification website.
- American Medical Association Physician Resources: Swine Flu
- Consultant Magazine H1N1 (Swine Flu) Center
 | Wikinews has related news: Swine flu cases worldwide top 1,000 |
- Pandemic Influenza: A Guide to Recent Institute of Medicine Studies and Workshops A collection of research papers and summaries of workshops by the Institute of Medicine on major policy issues related to pandemic influenza and other infectious disease threats.
- The Swine Flu Affair: Decision-Making on a Slippery Disease Report commissioned by the Department of Health, Education and Welfare, written by Richard Neustadt and Harvey V. Fineberg. An examination of what happened during and after the 1976 swine flu outbreak and lessons to help cope with similar situations in the future.
Nontechnical
- Why Revive a Deadly Flu Virus? By Jamie Shreeve - January 2006 New York Times - Six-page human-interest story on the recreation of the deadly 1918 H1N1 flu virus
- BBC News - 1918 flu virus's secrets revealed Results from analyzing a recreated strain.
- Publicly available data
- Oral history by 1918 pandemic survivor
Technical
- Recent influenza A (H1N1) infections of pigs and turkeys in northern Europe
- Epidemiologic Notes and Reports Influenza A(H1N1) Associated With Mild Illness in a Nursing Home -- Maine
- Swine Influenza Vaccine, H1N1 & H3N2, Killed Virus
- Influenza Virus Infections of Pigs
- H1N1-influenza as Lazarus: Genomic resurrection from the tomb of an unknown
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