H5N1 Forgotten (Almost), But Not Gone

While the world's flu fighters have concentrated on countering the H1N1 swine flu pandemic, avian influenza H5N1 has quietly continued to take its toll on both poultry and humans. Last year, 17 countries, stretching from Côte d'Ivoire and Germany to China and Japan, reported outbreaks of H5N1 in domestic poultry and wild birds; and the World Health Organization, which still says H5N1 poses a pandemic threat, recorded 72 human cases, 32 of them fatal.

The brunt of the outbreak, entering its eighth year, is still in China and the developing countries of Southeast Asia. Indonesia alone accounted for 19 of the 32 H5N1 deaths; Vietnam, for 5 and China, for 4. But there are glimmers of progress.

The number of human deaths has been dropping since peaking at 79 in 2006. And fewer countries reported outbreaks in 2009 than in 2008. Countries are refining responses to outbreaks, as was in evidence at the Asian Partnership on Emerging Infectious Diseases Research meeting in Kunming, China, from 13 to 16 January.

Partnership researchers from Cambodia, China, Indonesia, Laos, Thailand, and Vietnam compared notes on the effectiveness of control measures. Scientists reported that carefully targeted culling can be just as effective as widespread culling, and less disruptive. Others reported that reducing risk among those keeping backyard poultry has to be a community-wide effort, since changing the practices of individual farmers has proven difficult.

In particular, Witthawat Wiriyarat, a veterinarian and virologist at Mahidol University in Bangkok told ScienceInsider that a 3-year-old regional surveillance network is making progress in sorting out the role of wild birds. Some waterfowl initially thought to be spreading the virus, such as the Asian openbill stork, are now known to quickly succumb to H5N1 infection, Wiriyarat says. But passerine species, or perching birds, are apparently carrying the virus without ill effects, says Fumin Lei, of the Chinese Academy of Sciences' Institute of Zoology in Beijing. He adds that there is a high correlation of outbreaks in poultry and passerine movements.

Wiriyarat says it is still unclear what is sustaining the outbreak, whether there is a natural reservoir for H5N1, and how the virus is passed between domestic and wild birds. But while that research continues, the most effective way to reduce the amount of virus in circulation is to control outbreaks in poultry, he says.