Hunting Bird Flu

The appearance of bird flu in Europe, and particularly the outbreak in Turkey, has created several scientific mysteries. Why, for instance, did the disease infect birds almost simultaneously in 13 provinces scattered around the country? Why were more people infected (21 so far) than in any other outbreak since the disease first began infecting humans in 2003? And why have so few of the Turkish victims died--four, perhaps five--compared with previous outbreaks, in which half the human cases proved fatal? As the Turkish outbreak enters its fourth week, most of the people who contracted the disease are now on the mend. One person appears to have caught the virus without getting sick at all.

Doctors and health officials, worried about the threat of a human pandemic, aren't even sure if these developments constitute good news or bad. Europe, though, is turning out to be a better place to study H5N1, the virus that causes bird flu, than Asia ever was. In nine years in Asia, the virus has infected only 144 people, killing 75, usually one or two at a time. As a result, scientists haven't had much chance to observe the way the disease behaves in humans. The outbreak in Turkey has given them an unprecedented opportunity to get to know their foe.

The most evocative mystery concerns the relative mildness of the virus in Turkey compared to Asia. Turks who have contracted the disease have fared relatively well. As of last week, several had already been released from the hospital, some of them only mildly ill. And all of those who died did not, unlike the survivors, get early doses of Tamiflu, the antiviral drug, which has to be administered within 24 hours to be effective. This doesn't sound like the killer disease we've been hearing about. "This could be as bad as H5N1 gets," says Angus Nicoll, an ECDC scientist working in Ankara. "It could be that the virus is in the throes of changing and becoming less pathogenic."

Scientists are quick to point out, however, that it's way too soon to write off H5N1 as a dud. Other explanations for why the Turkish death rate is lower have not been discounted. It could be, for instance, that people in Turkey are simply more resistant to the virus than Asians. Or perhaps Turkish authorities were able to detect cases more quickly. Scientists are waiting with particular interest to learn the lab results on a brother and sister in an Ankara hospital; the girl is only mildly ill, and the boy isn't sick at all. He was taken there as a precaution and then tested positive for the virus. If the virus has turned less deadly, it may actually be more worrisome. Its mildness could enable it to spread more easily in people who have no symptoms, while the virus evolves the ability to pass to other humans. The answers to these questions will bear on how to combat H5N1 in future outbreaks.

The Turkish outbreak has also afforded scientists an opportunity to bring the latest in virus-hunting technology and techniques to bear. As the virus has made its way around the globe, it has been constantly mutating. To track the changes, scientists are using the latest genetic sequencing techniques, which give them a rapid turnaround--with some results in a few days. So far the news is inconclusive. The Medical Research Council lab in Britain has discovered a worrisome mutation in one of its Turkish samples, previously seen in an outbreak in Hong Kong, which made the virus better at infecting humans than chickens. So far, however, they've been able to rule out any recombination with human influenza. Gene-sequencing information can confirm where the victim caught the disease--and so far that seems in every case to be from birds directly. "It's not clear yet that the situation we're observing in Turkey, the number of infections, the virulence, is any different than what we've been seeing in Vietnam," says MRC's Alan Hay. For now, scientists are putting their hopes and fears on hold, and just trying to unravel the virus's genetic secrets.

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