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zoom RSS ブタインフルエンザの追跡監視は不十分

<<   作成日時 : 2010/06/22 20:07   >>

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画像 木曜日の発表された香港の研究によると、昨年のパンデミック・インフルエンザは現在中国のブタで感染が持続しているが、ウイルス遺伝監視がほとんどなされていないと言う。危険な新型は出現していないが、1月に細胞に付着する突起である表面蛋白の1つに新型が見つかった。別のブタ新型が容易に人に感染するようになるという合図でもあり、用心深く見守る必要がある。ブタはヒト型とトリ型の両方のインフルエンザに感染するので、ブタの中で8つの遺伝子が交換され新たな組み合わせが発生してブタに広がり、結局はヒトに達するという意味で重要である。
 米国と西ヨーロッパでは巨大豚飼育場では規則的に検査がされているが、小さい農場や、アジア・南米の大規模飼育場での数百万頭のブタはめったに検査されることがない。
 昨年のブタ・インフルエンザは構成する8つの遺伝子が米国とユーラシアでのブタから過去10年間に見つかっていることから命名されたものだが、メキシコでは見つかっていない。また、過去のヒトやブタの標本からも見つかっていないので、どこからきたかは依然謎のままである。
 いまや200カ国で感染し、さらにまた中国のブタにも感染し、時々長い間ブタかぜとして知られている2つの遺伝子と混ぜ合わさっていることが明白となってきた。

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Study Criticizes Swine-Flu Follow-Up
By DONALD G. McNEIL Jr.
Published: June 17, 2010
http://www.nytimes.com/2010/06/18/health/18flu.html

There is too little genetic surveillance of last year’s human pandemic flu, which has gone on to infect pigs in China and is readily mixing with other flus there, according to a study released Thursday by researchers in Hong Kong.

No dangerous new strain has emerged, said several experts who saw the study. But in January the researchers found a new strain with one of the pandemic flu’s surface proteins ― the outer spikes and knobs it uses to attach to cells. That was a reminder of how easily another swine strain capable of spreading among people could emerge.

“Just because we’ve just had a pandemic does not mean we’ve decreased our chances of having another,” said Dr. Carolyn B. Bridges, an epidemiologist in the flu division of the Centers for Disease Control and Prevention. “We have to stay vigilant.”

While there is “a long global history” of testing humans in many countries to see how human flu strains shift each year, there are “major gaps” in testing pigs, Dr. Bridges said.

That is important because pigs can catch both human and bird flus. Flus easily swap their eight genes and any new combination might be able to spread among pigs and eventually reach another human.

Pigs in the giant hog-raising barns of the United States and Western Europe are tested regularly, but the millions of pigs on small farms and in big operations in Asia and Latin America seldom are.

Commercial hog operations do constant testing so they can formulate new vaccines and snuff out flu outbreaks. Flu seldom kills pigs, but it makes them lose weight, which cuts into profits.

In the new study, published online in the journal Science, the Hong Kong researchers sequenced viruses they found by regularly swabbing pigs’ snouts at the territory’s largest slaughterhouse, which gets pigs from all over southern China. That testing, supported by a United States government grant, has gone on for 12 years.

“The message from our paper is not an inevitable disaster around the corner, but the need for continued vigilance,” Malik Peiris, a flu expert at the University of Hong Kong and one of the study’s authors, said in an e-mail message.

Among the globe-circulating flus that pigs could, in theory, catch are six swine flus, several human seasonal ones and at least two avian ones. The latter include the feared H5N1, which has killed 60 percent of the 500 people known to have caught it since 2003 but thus far almost never spreads from person to person, and an H9N2, which has been found in about a dozen humans but caused only mild disease so far.

Last year’s pandemic was originally dubbed a “swine flu” because the eight genes in its makeup had been seen before in American or Eurasian pigs during the previous 10 years, though never in the exact combination that was making people sick in Mexico.

It has not been found in any stored samples from people or pigs, so where it came from remains a mystery.

It has now reached 200 countries and is still infecting more people every day, though most cases are mild to moderate. It is now clear that it is also circulating freely in pigs in China and sometimes mixing genes with at least two other long-known swine flus.

“The implication of this study is that we have to be very careful,” said Dr. Peter Palese, a flu researcher at the Mount Sinai School of Medicine. “On the other hand, I can argue that it hasn’t happened yet. It’s not clear that any of these new swine viruses have the potential to go into humans and cause problems.”

----------------------------------------------------
Science 18 June 2010:
Vol. 328. no. 5985, p. 1529
DOI: 10.1126/science.1189132

Reassortment of Pandemic H1N1/2009 Influenza A Virus in Swine

D. Vijaykrishna,1,2,*,{dagger} L. L. M. Poon,1,* H. C. Zhu,1,2 S. K. Ma,1 O. T. W. Li,1 C. L. Cheung,1 G. J. D. Smith,1,2,{dagger} J. S. M. Peiris,1,{ddagger} Y. Guan1,2,{ddagger}

The emergence of pandemic H1N1/2009 influenza demonstrated that pandemic viruses could be generated in swine. Subsequent reintroduction of H1N1/2009 to swine has occurred in multiple countries. Through systematic surveillance of influenza viruses in swine from a Hong Kong abattoir, we characterize a reassortant progeny of H1N1/2009 with swine viruses. Swine experimentally infected with this reassortant developed mild illness and transmitted infection to contact animals. Continued reassortment of H1N1/2009 with swine influenza viruses could produce variants with transmissibility and altered virulence for humans. Global systematic surveillance of influenza viruses in swine is warranted.

1 State Key Laboratory of Emerging Infectious Diseases and Department of Microbiology, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong Special Administrative Region, China.
2 International Institute of Infection and Immunity, Shantou University Medical College, Shantou, Guangdong 515031, China.


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