SEOUL, Jan. 27 (Xinhuanet) -- South Korea has tightened quarantinemeasures for those returning from abroad after bird flu hit a poultry farm in the central part of the country again, killing 3,500 chickens, according to the Ministry of Agriculture and Forestry Tuesday.

    "Bird flu recurred in a province where first outbreak was reported late last year, and Southeast Asian countries reported confirmed cases, so we adopted strengthened quarantine measures for those returning from abroad," Kim Chang-seob, chief of the animal health division at the ministry, was quoted by Yonhap News Agency as saying.

    In cooperation with the (South) Korea Customs Service and otherrelevant ministries, the agriculture ministry increased the numberof quarantine officials at ports of entry and established more quarantine centers, Kim said.

    The ministry on Monday confirmed a chicken farm in Cheonan, some 92 kilometers south of Seoul, was hit again by the bird flu.

    It was a new bird flu case reported in 13 days. Up to now, a total 17 poultry farms have been confirmed to be infected by the Highly Infectious Avian Flu since the first outbreak on Dec. 15, 2003.

    About 3,500 chickens at the farm in Cheonan died of the H5N1 virus, and the rest 20,000 chickens were slaughtered. Quarantine officials planned to cull 214,000 poultry in a radius of 500 meters, reported Yonhap.

    South Korea has culled nearly 2 million chickens and other fowlto stem the spread of the highly contagious disease, which appeared to have been brought under control at the beginning of January.

    Quarantine officials in the field have warned that a few signs of a possible recurrence, including a drop in egg-laying rate, remained present, prompting the authorities to stay on alert.

    There were, however, no signs that the disease has crossed the species barrier to humans in South Korea. None of the more than 1,500 people was believed to have been exposed to the flu tested positive, health officials said.

    Officials said the local outbreak of avian flu was a different variant of H5N1 from the one which has surfaced in Vietnam.

    Although most strains of the H5N1 are not transmittable to humans, South Koreans are avoiding eating chicken or duck, causingprices to plummet. Enditem