-- AIWEB --

Care must be taken when describing and discussing avian influenza to avoid confusion. The terms avian influenza, avian influenza virus, human influenza, highly pathogenic avian influenza, pandemic influenza, and H5N1 cannot be used interchangeably. The following table (Table 1) lists commonly used avian influenza terms and provides definitions and usage guidelines.

Table 1. Definitions and usage guidelines for a selection of terms commonly used when discussing avian influenza.

Term	Acronym	Definition and usage
Avian flu*		Used colloquially and by the media, and often used wrongly, to refer to HPAI in poultry and/or humans – because its use can cause great confusion, it is better to avoid it, even when referring to poultry or other species of birds.
Avian influenza*	AI	A disease of birds caused by an influenza A virus – it is not a virus. Only use the term “avian influenza” to refer to the disease in poultry or other bird species – and remember that “avian influenza” can refer to either low pathogenic or highly pathogenic forms of the disease (LPAI or HPAI). Infection does not necessarily produce clinical disease.
Avian influenza virus	AIV	The aetiological (causative) agent of avian influenza.
Bird flu*		See Avian flu.
Enzootic/endemic		Prevalent among or presently constantly in a population in a specific geographic area. Endemic refers to human populations, while enzootic refers to populations of animals.
Genotype		Specific genetic composition of a virus, each subtype of AIV will have multiple genotypes. Genotyping AIVs aids epidemiological investigations.
Hemagglutinin	HA	Surface antigen on the influenza virus. Together with the neuraminidase (NA) antigen it defines the antigenic phenotype of the virus, which in turn, classifies influenza A viruses into subtypes.
Highly pathogenic avian influenza	HPAI	A severe disease in poultry and some other birds; has been associated with some H5 and H7 viruses; not all H5 and H7 viruses are highly pathogenic.
Low pathogenic avian influenza	LPAI	See avian influenza.
Neuraminidase	NA	Surface antigen on the influenza virus. Together with the hemagglutinin (HA) antigen it defines the antigenic phenotype of the virus, which in turn, classifies influenza A viruses into subtypes.
Pathogenic		Causing disease or capable of doing so.
Poultry		Term referring to domestic birds bred for meat, eggs, feathers etc. including chickens, turkeys, ducks, geese, quail etc.
Prevalence		Proportion of individuals within a given population with disease at a given time.
Subtype		A classification of influenza A virus based on the antigenic phenotype, which is determined by the HA and NA antigens present on the virus. Subtype examples include H5N1, H5N2, H7N3, H13N9.
Virulence		Ability of an infectious organism to produce disease (similar to pathogenicity but more a factor of the virus rather than host response).
Waterbird		Species of birds that are ecologically dependent on wetlands for at least part of their annual cycle including e.g. wildfowl, waders, gulls, herons, grebes, auks etc.

* Do not use the terms “bird flu”, “avian flu” or “avian influenza” to refer to human disease, even when it is a question of influenza in humans caused by infection from HPAI – the correct term to use, even though it is lengthy, is “influenza in humans caused by a virus of avian origin”.

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