Influenza is a well-known viral disease that appears worldwide at fairly predictable times each year. There are three main types and several subtypes, each believed to have its genesis in an avian specie. Until the direct jump from poultry to humans in the 1997 outbreak of the H5 type in Hong Kong, the various viruses were all thought to have gone through intermediary amplification in swine. Influenza can be a moderately disabling infection in a small percentage of a population or a catastrophic pandemic that causes millions of fatalities, as was the case in 1918. More recently, vaccines specific to certain genotypes identified through a global monitoring system have been effective. Of course, these vaccines are not universally available, and not freely available to everyone anywhere.
Less predictable and less interdictable is influenza in avian populations. The disease may take the form of classical Fowl Plague, one of several moderately severe influenzas, or Highly Pathogenic Avian Influenza (HPAI). The last is a major concern of poultry breeders, due to historically high fatality rates and the efficiency and range in which the disease can be transmitted. Wild shore and water birds, and migratory waterfowl are the most likely hosts of the virus, and can fall victim themselves.