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Expansión del H5N1 en el sureste asiático antes de 2004


H5N1 viruses are known to occur in Asia and have been isolated from free ranging wildlife at several intervals throughout the years. HPAI (H5N1) has certainly been present in the region since the first detection of the infection in geese in 1996 (Guangdong province of China) but the analysis of the biological character of previous isolates of H5N1 would be a priority to understand the current epidemic.

After its first detection in 1996 in Guangdong province, the disease broke out in Hong Kong in 1997. A Goose/GD/96-like virus was later considered to be the origin of the H5 component of the 1997 Hong Kong H5N1 virus. The disturbing event of the 1997 epidemic was the transmission of the disease to humans (confirmed in 18 people), leading to the deaths of 6. The same year, the virus was also detected in geese in Guangdong province.

From 1999 onwards, virus circulation was detected in Hong Kong in avian species through blood testing, swabbing of cages and testing of faecal samples. It appeared that the number of H5N1 virus isolations from ducks and geese increased from 1999 to 2001.

In late 2000, the virus changed genetically, incorporating new genes from other influenza viruses. These genes were believed to be from influenza viruses derived from other aquatic birds.

In May 2001, an avian H5N1 influenza virus was isolated from duck meat that had been imported to the Republic of Korea from China.

In 2002, mortalities of wild birds due to HPAI were reported in Hong Kong. This was the first report of deaths in wild birds in Asia. An H5N3 virus was isolated from dead terns in 1961 in South Africa but, in other parts of the world, avian influenza viruses isolated from wild birds are low pathogenic.

In January 2003, the mortality extended to waterfowl (flamingo) in Kowloon Park, Hong Kong and later in the year (May 2003) the H5N1 virus was also detected in Japan in imported duck meat.