Animals

• The University of Wisconsin-Madison explains that influenza is found in a number of animal species, alongside the form of the illness found in humans. Commonly affected animals include poultry, horses, pigs and marine animals.
  
  

Avian Influenza

• The U.S. Government's Animal Welfare Information Center explains that forms of avian or bird flu are found in many areas of the world. The natural hosts of avian flu include ducks, shorebirds, and other species of wild aquatic birds. The symptoms can range from mild to severe, with some species having very high mortality rates.
  
  

Transference

• The American Veterinary Medical Association reports that many forms of animal influenza are able to transfer between species to become specific to the new host species. A 2004 outbreak of canine influenza was found to have begun in horses and transferred to racing greyhounds to become a new canine-specific strain of influenza.