Epidemics of highly pathogenic avian influenza in Vietnam

An outbreak of highly pathogenic avian influenza (HPAI) caused by H5N1 subtype of avian influenza virus was reported in South Korea first outside China in December 2003. The outbreaks were continuously observed in eight Asian countries in the next 3 months. More than 100 million poultry were sacrificed in these countries. Vietnam was a country that was the most severely affected with the infection not only in poultry but also in human beings. A large number of domestic waterfowl such as ducks are rearing in Vietnam and other many Asian countries. The evidence is accumulated that HPAI viruses are maintained and circulating in waterfowl with latent infection. The waterfowl secrete viruses for long time and become a source of virus spreading. Characteristics of endemic viruses are changing genetically and antigenically during a bird-to-bird dissemination. Epidemiological aspects of HPAI (H5N1) in Vietnam are reviewed in this paper.