Human infections with avian influenza viruses.

Avian influenza A viruses are zoonotic agents that can cause outbreaks of acute respiratory disease in animals and man. The unprecedented re-emergence of highly pathogenic H5N1 influenza viruses in the human population has resulted in the deaths of 42 people and slaughter of millions of birds in Asia. The most striking features of this virus are its ability to infect and cause disease in a wide range of animals and to spread from person to person. There are also instances of infections with H7 and H9 subtypes in humans that are not discussed in this article. Therefore it is crucial to develop virologic surveillance programs for animal and human influenza, to limit the spread of the virus from infected poultry, and to develop efficacious vaccines by exploiting novel technologies such as reverse genetics.