The H5N1 virus occurs mainly in birds and does not usually infect people; however, more than 130 human cases have been reported by the World Health Organization since January 2004. Most of these have occurred after direct or close contact with infected poultry or contaminated surfaces. Few cases of human-to-human spread of the virus exist, and it has not continued beyond one person.
Influenza A (H5N1) virus -- also just called "H5N1 virus" -- is an influenza A virus subtype that occurs mainly in birds, is highly contagious among birds, and can be deadly to them.
Outbreaks of the avian flu H5N1 strain occurred among poultry in eight countries in Asia (Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam) during late 2003 and early 2004. At that time, more than 100 million birds infected with the H5N1 virus either died from the disease or were killed in order to try to control the outbreaks. By March 2004, the H5N1 outbreak was reported to be under control.
However, since late June 2004, new outbreaks of the H5N1 virus among poultry were reported by several countries in Asia (Cambodia, China [Tibet], Indonesia, Kazakhstan, Malaysia, Mongolia, Russia [Siberia], Thailand, and Vietnam). These outbreaks are believed to be ongoing.
Influenza H5N1 infection also has been reported among poultry in Turkey and Romania, and among wild migratory birds in Croatia. Human cases of H5N1 virus have also been reported in Cambodia, China, Indonesia, Thailand, and Vietnam.