Highly pathogenic notifiable avian influenza (HPNAI) is a serious, highly infectious and often lethal respiratory disease of birds and some mammalian species, including humans, cats, dogs, and mink caused by particular serotypes of the Influenza A virus.

All serotypes of Influenza A virus are widespread in nature in wild ducks, geese and shorebirds, but infection of these hosts does not usually produce clinical signs. The virus replicates in the airways and in the cells lining the intestinal tract, and is shed into the environment though the nasal excretions and faeces. Any susceptible host coming into contact with this can become infected. Poultry (fowls, turkeys, quail and ducks) are highly susceptible to infection with influenza A viruses but these can generally be classified into two categories: low pathogenic avian influenza (LPAI) viruses that typically cause little or no clinical signs in poultry, and highly pathogenic notifiable avian influenza (HPNAI) viruses that can cause severe signs and high mortalities in poultry. The term “notifable” refers to viruses of the H5 an H7 serotypes, as these have the potential to cause serious disease and epidemics.

The various serotypes are determined by the combination of two major antigens coating the virus surface, viz. the hemagglutinin (H) and neuraminidase (N) glycoproteins. 16 different H and 9 different N types have been discovered thus far, and can occur in any combination to form the serotype, e.g. H5N1, H1N1 etc. However, only two of the “H” subtypes, viz. H5 and H7 cause the scale of outbreaks that require the presence of the virus to be notifiable to the World Organization for Animal Health (OIE).