Characterization of H5N1 influenza viruses that continue to circulate in geese in southeastern China

The H5N1 influenza virus, which killed humans and poultry in 1997, was a re assortant that possibly arose in one type of domestic poultry present in th e live-poultry markets of Hong Kong. Given that all the precursors of H5N1/ 97 are still circulating in poultry in southern China, the reassortment eve nt that generated H5N1 could be repeated. Because A/goose/Guangdong/1/96-li ke (H5N1; Go/Gd) viruses are the proposed donors of the hemagglutinin gene of the H5N1 virus, we investigated the continued circulation, host range, a nd transmissibility of Go/Gd-like viruses in poultry. The Go/Gd-like viruse s caused weight loss and death in some mice inoculated with high virus dose s. Transmission of Go/Gd-like H5N1 viruses to geese by contact with infecte d geese resulted in infection of all birds but limited signs of overt disea se. In contrast, oral inoculation with high doses of Go/Gd-like viruses res ulted in the deaths of up to 50% of infected geese. Transmission from infec ted geese to chickens occurred only by fecal contact, whereas transmission to quail occurred by either aerosol or fecal spread. This difference is pro bably explained by the higher susceptibility of quail to Go/Gd-like virus. The high degree of susceptibility of quail to Go/Gd (H5N1)-like viruses and the continued circulation of H6N1 and H9N2 viruses in quail support the hy pothesis that quail were the host of origin of the H5N1/97 virus. The ease of transmission of Go/Gd (H5N1)-like viruses to land-based birds, especiall y quail, supports the wisdom of separating aquatic and land-based poultry i n the markets in Hong Kong and the need for continued surveillance in the f ield and live-bird markets in which different types of poultry are in conta ct with one another.