A dangerous new strain of bird flu that emerged in South Korea on 17 January has spread nationwide despite efforts to clamp down on the virus. Authorities have culled 2.8 million domestic chickens and ducks since the outbreak began, and the strain has also killed dozens of Baikal teal and other migratory birds. As yet, there are no reports of human infections. Scientists are puzzling over where the H5N8 strain, never before seen in a highly pathogenic form, originated. And researchers are scrambling to keep the virus out of the country's premier poultry research center.

Intensive surveillance of commercial poultry and wild birds had never before detected the H5N8 strain in Korea, says Jae-Hong Kim, a veterinary microbiologist at Seoul National University. Last year, a Chinese group reported having isolated it from apparently healthy ducks at a live poultry market in China. Based on H5N8’s sudden appearance in Korea and the genetic similarity of isolates from poultry and migratory birds, a governmental investigative committee has "tentatively concluded that [the virus] was likely to have been introduced by migratory birds," Kim says.

Conservationists are scoffing at that conclusion. "If birds are sick with the flu they are not going to fly thousands of kilometers," says Judit Szabo, science officer for the Seoul-based East Asian–Australasian Flyway Partnership, a group representing 15 Asia-Pacific nations and nongovernmental organizations. Szabo, a bird conservation biologist, speculates that migratory birds may have carried a mild form of the virus to Korea, where it spread into commercial poultry farms that provide "perfect conditions for a virus to get pathogenic really quickly." She says that on the first infected farms the virus caused only a drop-off in egg production, but then it mutated into a deadly strain as it spread. Wild birds then picked up the highly pathogenic form of H5N8 from farm wastewater, Szabo says. In a statement on its website, the partnership calls wild birds the victims of bird flu, not the perpetrators.

As scientists spar over H5N8’s origins, the virus has reached the doorstep of the National Institute of Animal Science (NIAS). A wild goose infected with the virus was found dead on 1 February just 10 kilometers from the institute's Suwon campus near Seoul. The facility houses more than 13,000 hens and nearly 5000 ducks for research on breed improvement and animal husbandry. "If the virus infects the facility, we would cull all of the poultry," says Yong-sup Song, who heads the NIAS contingency team. That would put a serious dent in the center's genetic resources and set back ongoing research programs.

"We are nervous, fighting against the possibility of infection," Song says. To keep H5N8 at bay, all of the center's 263 staff members have been on round-the-clock duty since 2 February, disinfecting facilities, chasing migratory birds away, and controlling human and vehicle traffic.

If those efforts fail, all is not lost. NIAS keeps an equal number of poultry at another campus 50 kilometers away. "We believe there is little chance of the virus simultaneously infecting both facilities," Song says.

With reporting by Mi-Young Ahn.