Experts pressure China for samples that can be analysed.
The deaths in China of more than 1,000 migratory birds from the flu strain H5N1 has left experts struggling to square the outbreak with their knowledge of the virus. At the same time, rumours are beginning to circulate that humans in the region have also fallen victim to the disease — although official sources have so far denied this.
The H5N1 strain has killed at least 53 people in Asia since late 2003, and is seen as one of the prime candidates for sparking a human pandemic. Migratory birds can act as carriers of flu, but their role in spreading highly dangerous strains such as H5N1 remains a matter for debate.
Until the latest outbreak, only a handful of migratory birds were known to have died from H5N1. This led some experts to suggest that the migrants are asymptomatic carriers of the virus, causing the occasional outbreak among poultry populations along their migration routes. Others believed that the small number of deaths among migrants were simply the result of wild birds picking up the infection from local ducks or chickens.
But the revelation on 21 May that at least 500 wild birds across five different species had died from the virus has dramatically altered the situation. With H5N1 now seeming to be highly infectious and lethal among the migrants, experts fear that the virus's genes may have mutated or reassorted.
To find out, the World Health Organization (WHO) is pressuring China to release samples for sequencing and analysis. “This is an exceptional case,” says Maria Cheng, the WHO's spokeswoman in Beijing. “We want to see the virus as soon as we can.”
China had not reported any cases of H5N1 in people or birds since a previous poultry outbreak ended in June 2004. But several Internet sites including ProMED-mail, an online database of health-related news, are now reporting that people are dying as a result of the latest outbreak (see ‘China rejects Internet claims of human cases’). Some sources are claiming there have been up to 120 fatalities.
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