Why does avian influenza subtype H5N1 cause so much concern?
The magnitude of the most recent series of outbreaks of highly pathogenic avian influenza, which began in Southeast Asia in late 2003, is the largest and most severe on record. Never before in the history of this disease have so many countries been affected. The disease and attempts to halt its spread have resulted in the death or destruction of an estimated 250 million birds. The H5N1 virus is now considered endemic (regularly found) in many parts of Indonesia and in some parts of China, Egypt and Nigeria. Establishing control of this disease in poultry is expected to take several years. H5N1 is predominantly a disease in certain species of birds. However, the widespread persistence of H5N1 in poultry populations poses two main risks for human health. The first is the small risk of direct infection when the virus passes from poultry to humans and causes severe disease. Of the very few avian influenza viruses that have infected humans, the current H5N1 virus has caused the largest numb
