Agrowing concern has focused on the recentdentification of influenza A H5N1 virus in Asia.Previously thought to infect only wild birds andpoultry,H5N1 has now infected humans,cats,pigs,and other mammals in an ongoing outbreak,oftenwith fatal results.According to a report from theWorld Health Organization(WHO),217 humanH5N1 cases have been confirmed and 123 of themhave been fatal as of May 19,2006.But manyquestions remain unanswered,for example how theH5N1 virus could cross species barriers and acquirethe ability to infect humans;when and how the H5N1virus will transmit effectively between humans andcause an influenza pandemic;and what are the 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 themhave been fatal as of May 19, 2006. Many many claims remain unanswered, for example how the H5N1 virus could cross species barriers and acquire the ability to infect humans; when and how the H5N1virus will transmit effectively between humans and cause an influenza pandemic; and what are the