摘要
Agrowing concern has focused on the recent ,identification of influenza A H5N1 virus in Asia. Previously thought to infect only wild birds and poultry, H5N1 has now infected humans, cats, pigs, and other mammals in an ongoing outbreak, often with fatal results. According to a report from the World Health Organization （WHO）, 217 human H5N1 cases have been confirmed and 123 of them have been fatal as of May 19, 2006.1 But many questions remain unanswered, for example how the H5N1 virus could cross species barriers and acquire the ability to infect humans;
Agrowing concern has focused on the recent ,identification of influenza A H5N1 virus in Asia. Previously thought to infect only wild birds and poultry, H5N1 has now infected humans, cats, pigs, and other mammals in an ongoing outbreak, often with fatal results. According to a report from the World Health Organization （WHO）, 217 human H5N1 cases have been confirmed and 123 of them have been fatal as of May 19, 2006.1 But many questions remain unanswered, for example how the H5N1 virus could cross species barriers and acquire the ability to infect humans;
