Avian Influenza: Type A Virus Infection in Humans

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Introduction The avian influenza virus is a type A influenza virus which is normally found in birds. Wild birds are the natural hosts for all known influenza type A viruses. This includes waterfowl, gulls and shorebirds. Ironically wild birds do not normally show symptoms of the influenza virus however when avian influenza type A viruses are passed onto domesticated birds, they are extremely susceptible to highly pathogenic avian influenza (HPAI) with a mortality rate of 90% to 100%1. Avian H2, H5, H6, H7, H8, H9 and H10 are the subtypes that are the most likely to be transferred to humans. The subtypes of the avian influenza type A virus that routinely cause human influenza are H3N2, H2N2, H1N1 and H1N2. H1N1 was the virus that caused the Spanish influenza pandemic in 1918 that killed 20 million people as well as the Russian pandemic of 1977 which was less lethal1. Currently, only two influenza type A virus subtypes are in general circulation among humans, H1N1 and H3N2. So far, the spread of H5N1 from person to person has been rare, very limited and not sustainable. However, of the 271 cases of H5N1 in humans reported to the World Health Organization (WHO) 59.1% were lethal cases. The continued cases of human H5N1 outbreaks, although restricted, cause concerns of a new and highly lethal influenza pandemic possibly in the future for humans2. Most recently an H7N9 outbreak was reported in April 2013 in China by the World Health Organization. While it’s been documented that some cases of H7N7 have seen mild illness, most cases have seen patients with severe respiratory illness and approximately one third of the severe cases leading to death3. At this point, no indication has been made that a genetic reassortment has oc... ... middle of paper ... ...ternational Journal of Avian Science. April 2007; 149 (2); 424-425. doi: 10.1111/j.1474-919X.2007.00711.x 9. To KW, Ng K, Que T, et al. Avian influenza AH5N1 virus: a continuous threat to humans. Emerging Microbes & Infection. 2012; 1, e25; doi:10.1038/emi.2012.24 10. Novick L, Morrow C, Mays G. Public Health Planning and Preparedness for Pandemic Flu. In Public Health Administration Principles for Population-Based Management. 2nd ed. Sadbury, MA: Jones and Bartlett Publishers;2008 11. U.S. Department of Health and Human Services. Public health Emergency, News Release. Available at: http://www.phe.gov/Preparedness/news/Pages/international-flu-vaccine-120607.aspx Accessed on December 7, 2013. 12. Center for Disease Control and Prevention. Avian Influenza A (H7N9). Available at: http://www.cdc.gov/flu/avianflu/h7n9-virus.htm Accessed on December 8, 2013.

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