One thing is certain about avian influenza: it's deadly. All three people who contracted the H5N1 strain of the virus in China last year died. In the first six weeks of 2009, eight people have come down with bird flu, and five have died. Another thing is that while the disease has yet to go pandemic, as many doctors fear it could, it remains worrisomely persistent. Every year since 2003, about 100 people in Asia, the Middle East and Africa contract the disease. Last year, in a rare exception, the number dropped below 50.
But bird flu, it seems, is back. Last month's five deaths one of the highest tallies of bird-flu deaths China has ever recorded in a month were in locations as far removed from one another as Beijing in the north, Xinjiang in the west, Guangxi in the south, Hunan in the center and Shandong in the east. "From a disease-control perspective, the increase in cases in China is notable, as is the wide geographic spread," says Dr. Hans Troedsson, the World Health Organization's representative in China. There is still no evidence that the virus has mutated to spread easily between humans, he says. But while such a nightmare scenario, which could set off a global flu pandemic that could kill millions, has shown no signs of being an immediate threat, serious concerns remain. "The fact that this is the highest number for a single month in China reminds us that the virus is entrenched and circulating in the environment," Troedsson says. (See pictures of the resurgence of bird flu.)
On Feb. 10, authorities in the far-Western region of Xinjiang culled more than 13,000 chickens in the city of Hotan after 519 died in a bird-flu outbreak. But until this week, China had reported no widespread outbreaks of the virus among bird populations, prompting concerns among some public-health experts that mainland health and veterinary authorities could be missing or even concealing the spread of the disease through poultry and wild birds. Hong Kong, where the first human cases of H5N1 infection were found in 1997, reported finding a dozen birds with the deadly strain of the virus earlier this year a strong indication that the virus is very likely present in adjacent Guangdong province. But so far, Guangdong has reported no bird cases. Equally unusual is that after such a busy month of infections in China, reports of human cases have gone silent. "It's a surprise for me, since in January, the human cases, you have so many, but in February it suddenly stops," says Dr. Guan Yi, a virologist from the University of Hong Kong. (Read "Is Hong Kong's Bird-Flu Vaccine Failing?")
The human deaths in China, plus new outbreaks among poultry in neighboring Vietnam and northeast India, indicate the likelihood of a firm presence of the virus on the mainland. Some experts worry that China could be missing the disease's deadly progression. Last week Dr. Lo Wing-Lok, an adviser to the Hong Kong government on communicable diseases, said the mainland had not been forthright about the spread of bird flu in poultry. "There's no doubt of an outbreak of bird flu in China, though the government hasn't admitted it," he told Bloomberg. Yu Kangzhen, the Ministry of Agriculture's chief veterinarian, responded in an interview with the state-run Xinhua news service that human bird-flu cases are not necessarily linked with animal cases. (Read about living with bird flu in Indonesia.)
If mainland investigators are missing the virus, it may be because efforts to block it are inadvertently hiding it. China developed an avian-influenza vaccine for poultry in 2005 and inoculates millions of birds annually. But not everyone agrees it's a panacea. In 2005 Robert Webster, an influenza expert at St. Jude Children's Research Hospital in Memphis, Tenn., suggested that China may have been using substandard vaccines that stopped symptoms of bird flu in poultry but allowed the virus to continue to spread. Recently, Guangzhou-based expert Zhong Nanshan also said there is a danger that China's widespread vaccinations could conceal the virus. "Special attention should be paid to such animals, including those that have been vaccinated," the Xinhua news service quoted him as saying on Feb. 6. "The existing vaccines can only reduce the amount of virus rather than totally inactivating it."
Mainland controls may be lacking another layer of more basic prevention in the way that live-chicken markets, prevalent throughout Asia, are inspected. Some worry that Chinese monitors may be calling for culls only when a large number of poultry become sick, as in Hotan this week, when 519 birds died. In contrast, last year Hong Kong culled thousands of birds after a regular inspection found only infected chickens in a wet market. The infected birds, experts say, showed no external signs of disease and could have been missed if inspectors were screening only birds that were dead or visibly ill.
Ramping up preventive measures may increasingly be a matter of life and death. Since bird flu re-emerged in 2003, 254 people in 15 countries have died of it. Researchers fear that other crises like global warming and the global recession have crowded the virus out of the news. But the disease survives in the limelight or out of it. "The point is, this virus has not disappeared at all," says Malik Peiris, a virologist at the University of Hong Kong. "It kind of dropped off the radar screen of media attention, but the virus itself has increased its spread. It's not only entrenched in Asia, the Middle East, in Egypt, Africa, parts of India and Bangladesh. It's really a problem."