Human disease due to infection with AI viruses endemic to North American wild birds has not been reported. However, there are many avian influenza strains that are highly adapted to poultry populations worldwide.For the poultry industry, these viruses are an ever-present, economically-important cause of flock morbidity and mortality. Historically, these poultry-adapted viruses were not known to spill over to any significant extent into wild bird populations.Since 2002, highly pathogenic strains of an avian influenza virus subtype known as Asian Lineage H5N1 have caused extensive mortality events in both domestic poultry and wild birds in many regions of the world. Associated with these outbreaks have been a few cases of illness and death in humans having very close contact with infected birds. These cases have prompted concern that one of the strains might eventually acquire genetic characteristics necessary for sustained human-to-human transmission, thus becoming capable of causing a human flu pandemic. Each wave of this unprecedented, ongoing epornitic has been met with very costly eradication attempts, resulting in economic hardship, political tensions,and sometimes cultural resentments.
It is clear that wild, migratory bird populations have contributed to the spread of these viruses, though to what extent is unclear. Surveillance in both domestic and wild bird populations continues throughout much of the world, including North America. While these viruses have not been detected in North America, experimental work indicates that wild bird mortalities can be expected should one of these viruses gain entry.