Avian influenza in poultry and wild birds

Avian influenza is a viral disease that primarily infects birds, both domestic and wild. Certain strains of bird flu break the avian barrier and have been known to infect other animals and humans. Avian flu viruses are common among wild bird populations, which act as a reservoir for the disease. While rarely fatal in wild birds, avian flu is highly contagious and often fatal in domestic poultry, prompting strict biosecurity measures on farms. International trade restrictions imposed by countries to counter avian flu can have large economic effects. A strain of highly pathogenic avian influenza (H5N1) has spread throughout Asia since 2003, infecting mostly poultry, some wild birds, and a limited number of humans through close domestic poultry-to-human contact. The virus has also spread beyond Asia, reaching Europe in 2005 and the Middle East and Africa in early 2006. Over 250 million poultry have died or been destroyed internationally. The human mortality rate among the more than 250 people infected exceeds 50%. Fears that the virus could mutate to allow efficient human-to-human transmission and cause a human pandemic have prompted a massive political and public health response. Since wild birds can carry the highly pathogenic H5N1 virus, federal, state, and other agencies have increased surveillance of wild and migratory birds. Surveillance is particularly high in Alaska, where Asian and American flyways overlap. Migrating birds from Asia could carry the virus to Alaska and infect birds from the Americas on shared nesting grounds. The newly infected birds could carry the virus down North American flyways. The United States also has blocked imports of poultry and poultry products from H5N1-infected countries. Nonetheless, imports into Central and South America could introduce the virus to the Western Hemisphere, and subsequent wild bird migration could bring the virus north into the United States. The highly pathogenic H5N1 strain has not been detected in the United States. But surveillance has detected different, low pathogenicity strains in wild bird populations, including a low pathogenic H5N1. Even if highly pathogenic H5N1 is found in the Americas, it does not signal the onset of a global human pandemic. The virus apparently has not yet mutated to allow human-to-human transmission, and scientists disagree whether or when this may happen. Controlling avian flu in poultry, and to the extent possible in wild birds, is seen as the best way to prevent a human pandemic from developing -- by reducing the number of animal hosts in which the virus may evolve. Indemnity payments to compensate farmers for birds destroyed in eradication efforts are seen as an important element of increasing success in control efforts. Congressional agriculture committees have held hearings on avian influenza preparedness, and appropriators have increased funding for surveillance and other preparedness activities for poultry and wild birds.