Avian influenza: epidemiology and surveillance in New Zealand

Avian influenza: epidemiology and surveillance in New Zealand Avian influenza epidemiology Avian influenza (AI) refers to infection of birds with avian influenza A viruses of the family Orthomyxoviridae. These RNA viruses are widespread, highly contagious and extremely variable. AI viruses are most frequently recorded in waterfowl (defined for this paper as members of the order Anseriformes – ducks, geese, and swans), which are considered to be the biological and genetic reservoirs of all AI viruses and the primordial reservoir of all influenza viruses for birds and mammals (Webster et al. 1992; Stallknecht 1998; Perdue et al. 2000). Carriage of AI is also seen to a lesser extent among two families within the order Charadriiformes: the Laridae (gulls and terns), and Scolopacidae (waders). The Charadriiformes are considered of secondary importance, given that AI viruses are only detected seasonally and at low prevalence when compared to the Anseriformes (Olsen et al. 2006; Munster et al. 2007; Whitworth et al. 2007). Wild birds, particularly migratory waterfowl, may play a major role in the initial introduction of AI viruses into commercial poultry (Halvorson et al. 1985; Hinshaw et al. 1986). However, once AI becomes established in commercial poultry, wild birds have very little or no role in secondary dissemination (Nettles et al. 1985).