Bird Flu in Japan, origin a mystery

Main Category: Bird Flu / Avian Flu
Also Included In: Flu / Cold / SARS
Article Date: 17 Feb 2004 - 0:00 PDT

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Following the outbreak of bird flu in Yamaguchi Prefecture, a new case was confirmed Tuesday in Oita Prefecture.

The virus that triggers the disease is suspected to have been carried to Japan from abroad by migratory birds. However, the route of infection remains unknown as the new outbreak took place far from the previous one.

The site of the Oita outbreak is about 150 kilometers from the Yamaguchi site. The Agriculture, Forestry and Fisheries Ministry therefore believes the two cases may be unrelated.

The transmitting agent of the virus that caused the outbreak in Yamaguchi Prefecture initially was thought to be migratory birds because the location was close to South Korea, where a massive outbreak of bird flu was confirmed.

But some experts are skeptical about this theory. Instead, they strongly suspect that the virus was carried into Japan via humans or goods as they believe it is unlikely that migratory birds would approach poultry and infect them.

Takaaki Sugimura, a former professor at Kagoshima University specializing in virology said, 'The virus is more likely to have been carried (into Japan) on shoes, clothes or other items.'

The Oita case occurred not at a poultry farm, but at a lumber mill. The infected bantams there were kept as pets.

An official of the ministry expressed puzzlement over the latest case, saying, 'I don't think many people went to and fro (the location) to feed the birds or get eggs.'

If the virus was carried on humans, it is unlikely that one person was behind both outbreaks. It seems more likely that there was more than one infection route.

Sugimura said: 'Due to advances in transportation, we've no idea when the outbreak of a disease takes place. It's important to cooperate internationally in seeking a cause.'

Bird flu has been rampant worldwide, especially in Asia. Yet the main source of infection remains unknown.

According to the Office International des Epizooties, a Paris-based organization established to monitor animal diseases worldwide, cases of bird flu have been confirmed in 11 Asian countries, and the number of people infected with the virus totaled 28 in Vietnam and Thailand, causing the deaths of 20 people.

International research institutions are trying to track down the route of infection using methods such as examining the virus' genetic structure. Recent research showed the virus detected in Yamaguchi Prefecture was different from the one found in Vietnam and Hong Kong. But the whole picture of the epidemic has yet to be revealed.

Over the past 20 years, outbreaks of the disease caused by the avian influenza virus have broken out in the United States and European countries as well as in Asia.

Shigeru Omi, regional director of the Western Pacific Regional Office of the World Health Organization, said, 'We should assume the virus already existed in many locations in Asia.'

But the outbreak of bird flu in Yamaguchi Prefecture is the nation's first case in 79 years, and infections confirmed in Japan have been geographically limited. Many experts therefore believe the virus was carried here from overseas.

Prof. Hiroshi Kida at Hokkaido University's Graduate School of Veterinary Medicine, said, 'It's hard to determine the route of virus penetration only with the Yamaguchi case, but we might be able to track it down if we examine the virus detected in Oita Prefecture.'

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