"Avian influenza (AI) viruses infect wild birds and poultry (e.g., chickens). They are divided into two groups based upon the severity of the disease they produce in poultry: low pathogenicity AI (LPAI) viruses and highly pathogenic AI (HPAI) viruses. LPAI viruses occur naturally in wild birds but can spread to poultry where they generally cause minor illness. However, HPAI viruses are highly contagious and cause high mortality in poultry. While LPAI viruses pose little threat to human health, certain HPAI viruses have caused serious illness and even death. Of particular concern to public health are the HPAI H5N1 viruses that are spreading rapidly in some parts of the world. HPAI H5N1 viruses have caused the deaths of millions of birds and of over 140 people worldwide. These deaths have thus far been restricted to Asia, the Middle East, and Africa. As of October 2006, the HPAI H5N1 virus has not been found in the United States."
Occupational Safety & Health Administration: http://www.osha.gov/