INTRODUCTION
hosts(1,2) and influenza B viruses, long thought to be restricted to humans, have been found in pinnipeds(3).
Influenza A viruses belong to the most important genus for wildlife.
They are divided into subtypes according to the antigenic variation in their HA and NA proteins. To date, 16 HA and 9 NA subtypes have been described. Wild waterbirds are the natural reservoirs of all influenza A virus subtypes[1] [2]. Influenza A viruses may also spread from wild birds or poultry to mammalian species, in which they may become established. In this way, influenza A viruses have become endemic in human, horse and pig populations. In addition, equine influenza A viruses have infected and potentially established in dog populations[3].In wild waterbirds, influenza A viruses primarily cause an intestinal tract infection in the absence of clinical disease. Such low pathogenic avian influenza viruses (LPAIV) similarly cause an intestinal tract infection in poultry. However, upon evolution, by selection, into highly pathogenic avian influenza viruses (HPAIV) in poultry, they cause systemic infection with high mortality. In mammals, influenza A viruses typically cause a respiratory tract infection of variable clinical severity and pneumonia as a primary complication. HPAIV H5N1 forms an exception, as it may cause severe systemic infection in mammals.
Infectious Diseases of Wild Mammals and Birds in Europe, First Edition. Edited by Dolores Gavier-Widen, J. Paul Duff, and Anna Meredith. © 2012 Blackwell Publishing Ltd. Published 2012 by Blackwell Publishing Ltd.