毒力弱的禽流感病毒株可感染人类

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一项新的研究第一次报道了毒力弱的禽流感病毒株能够从禽类传播给人类。

穿越物种屏障是流感病毒能在全世界流行的重要一步。以前的研究主要集中于致病力强的病毒株，如亚洲流行的h5n1型禽流感，就是从禽类传播给人类的。新的研究表明低致病力的病毒株也能传播给人类，只要给它们与人类株进行基因交换的机会，而且最终会发展成致病力强的病毒。

意大利的研究者对1999-2003年爆发的禽流感进行了研究，以确定人与禽类接触时感染禽流感的危险性。意大利北部禽流感的爆发主要发生在以饲养禽类为商业目的的农场。以前感染禽流感的人类病例主要是因为与被感染的禽类密切接触造成的，特别是那些生病或死亡的小鸡。

研究者对禽流感爆发时的暴露人群进行了血清学分析，从爆发区域的禽类农场工人取了983份血样，用不同的方法对血液进行检测以确保结果的准确性。

爆发主要涉及两种禽流感病毒的血清型：低致病力及高致病力h7n1型和低致病力h7n3型。一些暴露于最近低致病力h7n3型爆发的人群检测到h7n3阳性。这些被感染的人来自两个地区的不同农场，都和火鸡或小鸡有密切接触史。没有出现与感染相关的重度症状。

研究的作者isabella donatelli博士称，他们的研究第一次表明在家禽爆发禽流感时低致病力病毒株能够传播给人类。以前亚洲、加拿大和荷兰报道的人类感染都是高致病力病毒株导致的。

研究结果说明了不仅要在禽流感爆发时对高致病力的病毒株进行监测，而且还要在低致病力病毒株一出现就要进行监测。

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原始新闻和全文。
Less Virulent Strains Of Avian Influenza Can Infect Humans
ScienceDaily (Sep. 14, 2005) —

In findings with implications for pandemic influenza, a new study reports for the first time that a less-virulent strain of avian influenza virus can spread from poultry to humans. The research appears in the October 1 issue of The Journal of Infectious Diseases, now available online.
Crossing the species barrier is an important step in the development of a flu virus with pandemic potential. Previous studies have focused on the ability of highly pathogenic strains, such as H5N1 “bird flu” circulating in Asia, to spread from poultry to humans. The new study shows less pathogenic strains are also capable of jumping to humans, giving them the opportunity to swap genetic material with human strains, which could result in a more virulent virus.

Researchers in Italy studied outbreaks that occurred among poultry between 1999 and 2003, to determine the risk of avian influenza virus transmission to persons in contact with the animals. The outbreaks occurred in northern Italy in regions where the majority of the country's commercial poultry are raised on farms. Most previous cases of human infection with avian influenza viruses have involved close contact with infected poultry, particularly ill or dying chickens.

The investigators performed a serologic analysis of individuals exposed to infection during the outbreaks, collecting 983 blood samples from poultry farm workers in the outbreak regions. Blood was tested using three different techniques to ensure the validity of results.

The outbreaks involved two serotypes of avian influenza: one low and one highly pathogenic H7N1 and a low pathogenic H7N3 virus. Seven individuals exposed to the more recent outbreak of low pathogenic H7N3 tested seropositive for H7N3. The infected persons came from different farms in two locations and had close contact with turkeys or chickens. No serious symptoms were reported in connection with the infections.

The authors of the study, Dr. Isabella Donatelli of Istituto Superiore di Sanità in Rome and colleagues, noted that their work provides the first serologic evidence of transmission of low pathogenic strains of avian influenza virus to humans during an outbreak in domestic poultry. Previous reports of human infection in Asia, Canada, and the Netherlands have been associated, in contrast, with highly pathogenic strains. The investigators emphasized that their study probably underestimates the real infection rate of the two strains among exposed individuals, since blood samples were considered positive only if they repeatedly produced unequivocal positive results using several different serologic techniques. They commented, however, that very sensitive serologic techniques such as those developed in the study provide an efficient tool for preventing or controlling the spread of avian flu to humans.

The authors say their findings highlight the importance of improving disease surveillance not only during outbreaks of highly pathogenic avian flu, but also when less pathogenic strains are circulating. To forestall genetic exchange between human and avian strains, as in mixed infections, they emphasized that poultry workers should be systematically vaccinated, pointing out that such workers are identified as high-risk and included in the annual Italian vaccination campaign.

In an accompanying editorial, Frederick Hayden, MD, of the University of Virginia and Alice Croisier, MD, of the World Health Organization concluded, "The transmissibility of avian viruses may increase as the viruses adapt to humans. In affected countries, public education about simple precautionary measures for food preparation, poultry handling, and avoidance of contaminated water are essential until specific prevention measures such as vaccines become available."

全文是这个：
Serological Analysis of Serum Samples from Humans Exposed to Avian H7 Influenza Viruses in Italy between 1999 and 2003
摘要：
We evaluated the potential for avian-to-human transmission of low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI) H7N1 and LPAI H7N3 viruses that were responsible for several outbreaks of influenza in poultry in Italy between 1999 and 2003. A serological survey of poultry workers was conducted by use of a combination of methods. Evidence of anti-H7 antibodies was observed in 3.8% of serum samples collected from poultry workers during the period in 2003 when LPAI H7N3 virus was circulating. These findings highlight the need for surveillance in people occupationally exposed to avian influenza viruses, so that they can be monitored for the risk of avian-to-human transmission during outbreaks of avian influenza caused by both LPAI and HPAI viruses.

还有1篇研究LPAV的
Human Illness and Isolation of Low-Pathogenicity Avian Influenza Virus of the H7N3 Subtype in British Columbia, Canada