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Study finds key factors behind bird flu outbreaks
WASHINGTON (Reuters) - Ducks, people and rice paddies are the primary forces driving outbreaks of avian influenza in Thailand and Vietnam, and the number of chickens is less pivotal, scientists said on Wednesday.
U.N. Food and Agriculture Organization experts and others looked at three waves of H5N1 bird flu in Thailand and Vietnam in 2004 and 2005. The virus has killed 236 people in 12 countries since 2003.
They used computer modeling to study how various factors were involved in the spread of the virus, including the numbers of ducks, geese and chickens, human population size, rice cultivation and local geography.
Even though Thailand and Vietnam addressed the outbreaks in different ways, the researchers found that the numbers of ducks and people, and the extent of rice cultivation were the most important contributing factors underpinning the outbreaks.
\"This provides better insight on where and when the H5N1 risk is highest, so it's possible to better pinpoint where to look for the virus or where to expect flare-up of disease and also when to expect it,\" Jan Slingenbergh, senior veterinary officer for the Food and Agriculture Organization, said in a telephone interview.
\"It helps to better target the interventions,\" he added.
Monitoring duck populations for the H5N1 virus and tracking rice farming by satellite are the optimal ways to predict an outbreak's distribution, the researchers said. They added that their model also can be extended to Laos and Cambodia, where there are similar land use patterns.
Avian influenza has been closely linked to chickens in the past, but the study found the number of chickens to be less important as a predictor.
The findings were published this week in the journal Proceedings of the National Academy of Sciences.
\"In the past in Vietnam, there have been major (bird) vaccination exercises countrywide, which is an enormous effort in terms of logistics and time and effort and staff requirements,\" Slingenbergh said.
\"And there is fatigue, also, among the farmers and veterinarians. And if it's now possible to better time and localize the efforts, that is a major efficiency achievement.\"
The researchers said there are close ties between duck grazing patterns and rice cropping intensity. They said ducks feed mainly on leftover rice grains in harvested paddy fields, so free-ranging ducks may go to many different sites following rice harvest patterns.
The H5N1 avian flu virus has swept through flocks of poultry in Asia and sometimes in Africa and Europe. It has infected 373 people in 14 countries and killed 236 of them since 2003. Experts fear the virus may change just enough to pass easily from person to person, sparking a deadly pandemic.
华盛顿路透社电）科学家在周三宣布，鸭群、人类和稻田，是泰国和越南爆发禽流感疫情的温床，倒是鸡只的数量并不是最紧要的。
联合国粮农组织的多名专家和其他科学家，观察泰国和越南于2004年和2005年爆发三次禽流感疫情。从2003年至今，12个国家已有236人死于禽流感。
他们利用电脑模型，研究禽流感H5N1病毒蔓延的各种因素，包括鸡、鸭和鹅的数量、人口的多寡、稻米种植，以及当地的地理状况。
虽然泰国和越南防抗禽流感的方式不同，但研究员却发现鸭子的数量、居民和种稻情况，才是引发禽流感病毒蔓延的最重要因素。
粮农组织高级兽医Slingenbergh在接受电话访问时说：“这些数据使人更清楚看到禽流感爆发风险最高的地区和时间，因此，可能更好地点出到哪里去寻找病毒，或者疫情预计会恶化的地区和几时爆发。”
“这有助于更好地锁定防御计划。”他补充说。
研究员认为，监视鸭子数量来预测H5N1病毒，以及利用卫星追踪稻田情况，是预测禽流感病毒分布的最理想途径。他们又说，他们研发的模式，也适合于土地利用方式类似的老挝和柬埔寨。
过去认为禽流感同鸡有密切关系，但这次研究发现鸡只的数量，并非是重要的预测因素。
有关研究结果，已于本周在美国《国家科学院学报》上发表。
Slingenbergh说：“越南曾在全国推行大规模的禽流感免疫计划，意味着大量的后勤工作，时间、精力、人员要求等等。”
“农民和兽医都精疲力竭。如果现在能够善用时间和把资源分配到关键地区，等于取得了重大的成效。
研究员指出，放养鸭子和水稻栽种密度也有密切关联。鸭子以稻穗收割后遗留的谷粒为主食，因此鸭子可能跟随收割地段，四处游荡觅食。
H5N1禽流感病毒已在亚洲，或非洲、欧洲的家禽内散播。2003年以来已感染了14个国家的373人，并致死236人。专家担心，病毒可能已变化得能在人类间轻易传播，导致致命的流感爆发。
http://www.zaobao.com/special/birdflu/pages3/birdflu080328.shtml
亚洲，家禽，尤其在农村，多采用散养，现在看来这是与野禽能接触的地方，而这些地方也是禽流感防疫的薄弱地区，令人担忧。病毒变异到何等程度，现在不那么清楚，但是形势不容乐观哪。
上海巴斯德所几年前的讲座，记得说“鸭子即使得病，也有一半以上的概率能够活下来”。——也提示鸭类是天然宿主。
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发表于 2008-4-8 12:01:07