BEIJING, Aug. 26 (Xinhuanet) -- There are no pigs in the Chinese mainland infected with the H5N1 virus, or avian flu virus, and relevant research has reached no clear conclusion on H5N1 infecting pigs, announced the Ministry of Agriculture here on Thursday.

    In an experiment on isolation and identification of H5N1 and H9N2 of sub-type influenza virus in pigs, two strains of H5N1 were isolated from samples collected between 2001 and 2003, said Jia Youling, director of the Veterinary Bureau of the ministry, at a press conference.

    Upon receiving the results, the ministry began the verification process immediately, which showed that the research isolates were highly isogenous with the H5N1 duck virus isolated before. However,no new strains were isolated during the intense surveillance and study efforts, which suggested that it was an "incidental infection" by the duck-origin avian influenza (AI) virus, said Jia,also national chief veterinary officer.

    He noted that the ministry has kept sharp vigilance over any possibility of AI cross-species transmission and the infection of mammals. Since 1999, the ministry has called on institutes to carry out research activities on AI´s possible invasion of mammals.In addition, the epidemiological study was launched nationwide.

    After the outbreak of avian flu in some places in China this year, the ministry required local agencies to tighten up surveillance efforts on pigs when mapping out the AI monitoring arrangements.

    At the same time, the ministry required relevant institutes to continue and to intensify the research on the rules of genetic evolution of AI isolates as well as possible mammal infection mechanisms. The National AI Reference Lab, National Epizootics Research Center and Veterinary Diagnostic Center of the ministry were arranged to launch targeted surveillance and study of the possible carriage of AI virus by pigs.

    "The surveillance results show that no other H5N1 strain was isolated from pigs in the mainland," said Jia.

    "But it´s worth noting that carrying a virus does not mean infection. Similarly, the virus identified does not necessarily mean that there is a presence of an epidemic."

    "Once the epidemic breaks out, we will provide timely notification in accordance with the rules of international organizations," he said.

    In addition, due to the very limited strains isolated, no clear conclusion could be made on pig-to-human infection of H5N1. "But no matter whether there is a conclusion or not, we will certainly reinforce research programs on the relationship between H5N1 carried by pigs and avian flu infecting human beings. And by doing so, we will be able to prevent and control any outbreak if this kind," Jia noted.

    According to the ministry, studies from the international community indicate that the flu virus can infect not only poultry,but also mammals. There were reports of some mammals´ carriage of AI virus in Asia, such as cat, tiger, cloud leopard and pig.

    In 1918, the first swine flu case was reported in America. In 1931, the first H1N1 virus was isolated, followed by the H3, H4 and H9 sub-types from countries in Europe, Asia and North America.