Aug 18, 2005 (CIDRAP News) – An outbreak of a mild form of avian influenza was reported in Japan today, as the World Health Organization (WHO) voiced concern about the recent spread of H5N1 avian flu to Russia and Kazakhstan.

Japan"e;s Ministry of Agriculture reported that chickens at a farm in Konosu, near Tokyo, had tested positive for avian flu, according to the Chinese news agency Xinhua. "The virus detected is of the H5 variety but is considered to be a weaker type because no mass deaths occurred at the farm," the story said.

The local government has decided to kill the 98,300 chickens on the farm and ban the movement of chickens and eggs within 5 kilometers of the site, the report said.

An outbreak of H5N2 avian flu was reported on one farm elsewhere in Japan in June. H5N2 avian flu has not been known to infect humans, unlike the H5N1 virus, which has killed close to 60 people in Southeast Asia since late 2003. Japan had several poultry outbreaks of H5N1 early in 2004.

The WHO today released an assessment of the recent spread of H5N1 outbreaks to Russia, Kazakhstan, and the Tibetan region of China. "The expanding geographical presence of the virus is of concern as it creates further opportunities for human exposure," the agency said.

"Each additional human case increases opportunities for the virus to improve its transmissibility, through either adaptive mutation or reassortment. The emergence of an H5N1 strain that is readily transmitted among humans would mark the start of a pandemic."

The outbreaks in Russia and Kazakhstan are the first appearances of highly pathogenic H5N1 avian flu in the two countries, the agency said. It said deaths in migratory birds as well as domestic birds have been reported.

The flu virus that recently killed 89 migratory birds at two lakes in northern Mongolia has not yet been fully identified, though it is known to be type A, the WHO said.

"The outbreaks in Russia and Kazakhstan provide evidence that H5N1 viruses have spread beyond their initial focus in south-east Asian countries, where outbreaks are now known to have begun in mid-2003," the WHO said. The virus continues to crop up in many areas of Vietnam and Indonesia and in some areas of Cambodia, China, Thailand, and possibly Laos, the statement added.

The WHO suggested that the Qinghai Lake wildlife refuge in central China may be a link between the outbreaks in Southeast Asia and those in Russia. More than 6,000 migratory birds at the refuge died of avian flu in late spring and early summer.

Research published in July indicated that the H5N1 viruses found in the Qinghai Lake outbreak resembled those that have been circulating in Southeast Asia, the agency said. It added, "Analyses of viruses from the Russian outbreak, recently published on the OIE [World Organization for Animal Health] Website, show apparent similarity to viruses isolated from migratory birds during the Qinghai Lake outbreak."

The WHO warned that the virus could spread to still more countries. The agency called for careful surveillance for cases in poultry and migratory birds and quick efforts to contain any outbreaks.

Meanwhile, it remained unclear today whether some bird deaths in southern Russia, near the Caspian Sea, were due to avian flu. The Moscow Times quoted Sergei Dankvert, a top Russian veterinary official, as saying that the birds on a farm in Kalmykia might have died of an infection caused by parasitic worms. If the illness turned out to be H5N1 avian flu, it could mark the first outbreak of that strain in Europe, the story said.