(July 8, 2004 Beijing and Shantou) The Joint Influenza Research Centre (Shantou University Medical College/Hong Kong University) has published a study that shows H5N1, the highly pathogenic avian influenza virus, has become endemic in China and the East Asian region.
Results of the JIRC’s extensive 5-year study of the virus were published in Nature #431. The study showed that the H5N1 viruses are not easily eradicable, and pose a threat to public and veterinary health in the region and potentially the world. The JIRC suggested that governments implement sustainable control measures to reduce the frequency of H5N1 outbreaks and the probability of human infection.
To trace the ecological genetic origins of these outbreaks, the investigators compared H5N1 viruses isolated from poultry in Indonesia, Thailand and Vietnam as well as from humans in Thailand and Vietnam with H5N1 isolates obtained during prospective surveillance of live poultry markets in Hong Kong and in Guangdong, Hunan and Yunnan provinces from 2000 to 2004. Since 2001, H5N1 viruses have continued to surface in mainland China with a seasonal pattern, peaking from October to March, when the mean temperature falls below 20 degrees Celsius.
The timing and distribution of the H5N1 infection in poultry in China since 2001 coincides with the general period of winter bird migration to southern China. It is unclear whether the H5N1 virus has become established in wild bird populations. However, the potential role of wild birds in the circulation of H5N1 viruses must be considered in control strategies.
H5N1 is now endemic in poultry in Asia and is ecologically entrenched to present a long-term pandemic threat to humans. At present these viruses are poorly transmitted from poultry to humans, and there is no conclusive evidence of human-to-human transmission. However, continued, long-term human exposure to H5N1 viruses increases the likelihood that the viruses will acquire the necessary characteristics for efficient human-to-human transmission through genetic mutation or reassortment with a prevailing human influenza A virus.
Although other countries in the East Asian region have been affected, Hong Kong has implemented effective preventive measures and has remained remarkably free of H5N1 outbreaks in poultry in 2004.
The JIRC is supported by the Li Ka-shing Foundation and headed by Dr. K.S. Li and Dr. Y. Guan.