Bird flu might be less deadly than feared

 作者:向褥     |      日期:2019-03-02 01:15:02
By Debora MacKenzie H5N1 bird flu may be less deadly to people than feared, suggests a study in Vietnam, although the results will require more work to confirm. This might be good news if H5N1 ever starts spreading more readily among humans. But it is bad news if it means there are far more human infections with the virus, as it means more opportunities for the virus to adapt to humans. To date, about half the people confirmed to have H5N1 have died – a terrifying fatality rate. By comparison the 1918 pandemic flu virus killed just 3% it made ill. But it is possible that many mild or symptom-free H5N1 infections have gone undetected, meaning the real fatality rate is lower. One way of uncovering unreported H5N1 infections is to look for antibodies to the virus. Tests on nurses and doctors who have tended H5N1 patients have generally failed to turn up such antibodies. But what scientists do not know is whether people can catch it from sick poultry – as nearly all the severe cases so far have – and not fall seriously ill. The grandfather of people who fell ill with H5N1 in Vietnam in 2005 had antibodies but showed no known symptoms, as have a handful of Japanese and Hong Kong workers culling infected chickens. But this might have been after exposure to dead virus, and not from live virus infection. The new data come from a health study of 45,000 people in Ha Tay province, just south of Hanoi, conducted by Anna Thorson and colleagues from the Karolinska Institute in Stockholm, Sweden, since 2003. In 2004 the region was struck by H5N1 bird flu, though none of the study’s participants fell ill. Subjects were asked about any flu-like illness in the preceding months and their exposure to poultry. They found that adults aged 19 to 45 were twice as likely to have had a flu-like illness if they had handled sick or dead poultry than if they had simply had sick poultry around the house, or no sick birds at all. Cases also clustered in families, as have severe cases. “Awareness of bird flu in humans was very low and considered ‘something that happens to others’ at the time of the study in 2004,” says Thorson. That makes it less likely that people who handled sick chickens were worried about flu, and so inclined to imagine having it. There were no blood samples taken, but the team calculated that there could have been 750 cases of mild H5N1 in the group. But Jeremy Farrar, head of Oxford University’s Clinical Research Unit in Ho Chi Minh City, Vietnam, cautions that flu-like illnesses are common. “Without knowing whether these people have antibodies to H5N1, you can’t really draw any firm conclusions from these results,” he told New Scientist. Thorson agrees antibody work is needed. “We want to do it,” she said. “The main problem with a follow-up is probably the [low] sensitivity of the antibody test.” Antibody studies of healthy people in areas with H5N1 outbreaks are now underway, says Farrar. Bird Flu – Learn more about the flu pandemic that could kill millions in our continually updated special report. More on these topics: