The H5N1 virus is highly contagious among birds, but does not usually infect people. Even so, over 130 human cases have been reported by the World Health Organization since January 2004. Most of these cases are due to direct or close contact with infected poultry or contaminated surfaces. There are few cases of human-to-human spread of the virus. However, it has not continued beyond one person.
What Is the H5N1 Virus?
Influenza A (H5N1) virus -- also called just "H5N1 virus" -- is an influenza A virus subtype that occurs mainly in birds, is highly contagious among birds, and can be deadly to birds.
Outbreaks of the avian H5N1 virus 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 virus outbreak was reported to be under control.
Since late June 2004, however, 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). It is believed that these outbreaks are ongoing. Influenza H5N1 infection also has been reported among poultry in Turkey and Romania, and among wild migratory birds in Croatia. Human cases of the H5N1 virus have been reported in Cambodia, China, Indonesia, Thailand, and Vietnam.
The H5N1 virus does not usually infect people, but more than 130 human cases have been reported by the World Health Organization (WHO) since January 2004. Most of these cases have occurred as a result of people having direct or close contact with infected poultry or contaminated surfaces. However, there have been a few cases of human-to-human spread of H5N1 virus.
Of the few avian influenza viruses that have crossed the species barrier to infect humans, the H5N1 virus has caused the largest number of detected cases of severe disease and death in humans. In the current outbreaks in Asia and Europe, more than half of those infected with the virus have died. Most cases have occurred in previously healthy children and young adults. However, it is possible that the only cases currently being reported are those in the most severely ill people, and that the full range of illness caused by the H5N1 virus has not yet been defined.