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H5N1 HPAI in Different Species

3.2 Geese and H5N1 HPAI

Domestic geese (Anser domesticus) are believed to have played a key role in the evolution of Asian-lineage H5N1 HPAI viruses from the time they were first detected in 1996 and the emergence of multiple genotypes from 2000 onwards.

Geese were first found to be infected with the H5N1 HPAI virus in 1996 and again in 1997, and viruses similar to those found in 1996 were still circulating in geese from southern China in 1999 (Cauthen et al, 2000). By 2001, the original goose virus genotype was rarely encountered and was thought to have been replaced by a range of reassortants that often only retained HA and NA genes linked back to the original viruses (Guan et al, 2002b). Healthy geese were also found to be infected in Viet Nam in 2001 during market studies (Nguyen et al, 2005). These viruses differed somewhat from those found in 2003 and later.

Numerically, there are fewer geese (around 270 million) reared in Asia than ducks (about 930 million) and chickens (about 8.78 billion) (FAO, 2006), suggesting that they probably play a lesser role in the spread of infection than other infected species. Nevertheless, China still has a standing population of more than 268 million head of geese or 89 percent of the global goose population, which still represents a significant potential reservoir (FAO, 2006).

Because geese vaccinated with killed H5N1 vaccines do not appear to produce prolonged, high-level immunity under experimental conditions without the use of multiple, high doses of vaccine (Tian et al, 2005), these birds have the potential to play a role in virus persistence and spread if vaccination is used irregularly, especially if doses higher than those recommended for chickens are not used.