Animal-to-Human Transmission of Avian Influenza
Historically, influenza viruses are believed to cycle from birds to swine and from swine to people. Unique among animals, swine carry viral receptors for both human and avian influenza viruses. However, birds and people do not carry compatible receptors to permit a direct sharing of common influenza viruses. If swine are infected with both a human- and a bird-origin influenza virus, these viruses can hybridize (cross and share genetic information) and possibly create a more lethal human virus or create a more lethal bird virus. These processes occur on a yearly basis and are responsible for most human influenza viruses that emerge. The current H5N1 influenza is unique in that it appears to have been transmitted directly from birds to humans, without the usual swine intermediary.
The last two human influenza pandemics are believed to have originated in China, where there are large numbers of farm-raised poultry and swine in close proximity to a large, concentrated human population. This culture provides the conditions ideally suited for the development of the new influenza viruses.
- This document is VM138, one of a series of the Veterinary Medicine-Large Animal Clinical Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date June 12, 2002, reviewed and revised May 16, 2005.
- 2. Gary D. Butcher, DVM, Ph.D., Diplomate, American College of Poultry Veterinarians, University of Florida College of Veterinary Medicine, Gainesville, FL., Richard D. Miles, Ph.D., Professor, Poultry Nutritionist, Department of Dairy and Poultry Sciences, Amir H. Nilipour, PhD, Director of Investigation and Quality Assurance, Grupo Melo, S.A., Panama, Republic of Panama