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H7N9 is a bird flu strain of the species Influenza virus A (avian influenza virus or bird flu virus). Avian influenza A H7 viruses normally circulate amongst avian populations with some variants known to occasionally infect humans. An H7N9 virus was first reported to have infected humans in March 2013, in China.〔 Cases continued to be reported throughout April and then dropped to only a few cases during the summer months. At the closing of the year, 144 cases had been reported of which 46 had died.〔(WHO: Global Alert and Response: Human infection with avian influenza A(H7N9) virus – update ) (accessed November 7, 2013)〕 It is known that influenza tends to strike during the winter months, and the second wave, which began in October, was fanned by a surge in poultry production timed for Chinese New Year feasts that began at the end of January. January 2014 brought a spike in reports of illness with 96 confirmed reports of disease and 19 deaths. As of April 11, 2014, the outbreak's overall total was 419, including 7 in Hong Kong, and the unofficial number of deaths was 127.〔(Study says Vietnam at H7N9 risk as two new cases noted | CIDRAP )〕〔(#H7N9 Human Cases 2014 | pandemicinformationnews.blogspot.com )〕〔 (WPRO | Human Infection with Avian Influenza A(H7N9) )〕 The World Health Organization (WHO) has identified H7N9 as "...an unusually dangerous virus for humans." Most of the cases resulted in severe respiratory illness, with a mortality rate of roughly 30 percent.〔 〔 Researchers have commented on the unusual prevalence of older males among H7N9-infected patients.〔 While several environmental, behavioral, and biological explanations for this pattern have been proposed,〔 the reason remains unknown.〔 It has been established that many of the human cases of H7N9 appear to have a link to live bird markets.〔 As of January 2014, there has been no evidence of sustained human-to-human transmission,〔 however a study group headed by one of the world’s leading experts on avian flu reported that several instances of human-to-human infection are suspected.〔(Study puts troubling traits of H7N9 avian flu virus on display (July 10, 2013) )〕 H7N9 virus does not kill poultry, which makes surveillance much more difficult. Chinese scientists announced the development of a vaccine on October 26, 2013, but said that H7N9 had not spread far enough to merit widespread vaccination.〔〔 Research regarding background and transmission is ongoing.〔 ==H7N9 virus== Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA). The avian influenza A(H7N9) virus designation of H7N9 identifies it as having HA of the H7 subtype and NA of the N9 subtype. Avian influenza A H7 viruses are a group of influenza viruses that normally circulate among birds. H7 influenza infections in humans are uncommon, but have been confirmed world-wide in people who have direct contact with infected birds. Most infections have been mild involving only conjunctivitis and mild upper respiratory symptoms.〔〔 The avian influenza A(H7N9) virus is a subgroup among this larger group of H7 viruses. Although some H7 viruses (e.g. H7N2, H7N3 and H7N7) have occasionally been found to infect humans, H7N9 has previously been isolated only in birds, with outbreaks reported in the Netherlands, Japan, and the United States. Until the 2013 outbreak in China, no human infections with H7N9 viruses have ever been reported.〔〔 Genetic characterisation of avian influenza A(H7N9) shows that the H7N9 virus that infects human beings resulted from the recombination of genes between several parent viruses noted in poultry and wild birds in Asia. It is most closely related to sequences found in samples from ducks in Zhejiang province in 2011. Evidence so far suggests that the new H7N9 virus might have evolved from at least four origins. It is hypothesized that the gene that codes for HA has its origin in ducks and the gene that codes for NA has its origin with ducks and probably also wild birds. Six internal genes originated with at least two H9N2 chicken viruses. The HA genes were circulating in the East Asian flyway in both wild birds and ducks, while the NA genes were introduced from European lineages and transferred to ducks in China by wild birds through migration along the East Asian flyway.〔 Dr. Keiji Fukuda, WHO's assistant director-general for health security and environment, remarked at a Toronto interview that "I think we are genuinely in new territory here in which the situation of having something that is low path in birds (yet) appears to be so pathogenic in people... And then to have those genetic changes ... I simply don't know what that combination is going to lead to." "Almost everything you can imagine is possible. And then what's likely to happen are the things which you can't imagine," he also remarked. According to the deputy director of CDC's influenza division, the genetic makeup of H7N9 is "disturbingly different" from that of the H5N1 virus that has infected more than 600 people over the past 10 years and killed more than half of them. "The thing that's different between them is the H5 virus still maintains a lot of the avian or bird flu characteristics, whereas this H7N9 shows some adaptation to mammals. And that's what makes it different and concerning for us. It still has a ways to go before it becomes like a human virus, but the fact is, it's somewhere in that middle ground between purely avian and purely human."〔(Officials Prepare For Another Flu Pandemic — Just In Case : Shots - Health News : NPR )〕 In August 2013, it was announced that scientists plan to create mutant forms of the virus so they can gauge the risk of it becoming a lethal human pandemic. The genetic modification work will result in highly transmissible and deadly forms of H7N9, and is being carried out in several high security laboratories around the world. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Influenza A virus subtype H7N9」の詳細全文を読む スポンサード リンク
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