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

Abstract

The H5N1 influenza virus, which killed humans and poultry in 1997, was a reassortant that possibly arose in one type of domestic poultry present in the live-poultry markets of Hong Kong. Given that all the precursors of H5N1/97 are still circulating in poultry in southern China, the reassortment event that generated H5N1 could be repeated. Because A/goose/Guangdong/1/96-like (H5N1; Go/Gd) viruses are the proposed donors of the hemagglutinin gene of the H5N1 virus, we investigated the continued circulation, host range, and transmissibility of Go/Gd-like viruses in poultry. The Go/Gd-like viruses caused weight loss and death in some mice inoculated with high virus doses. Transmission of Go/Gd-like H5N1 viruses to geese by contact with infected geese resulted in infection of all birds but limited signs of overt disease. In contrast, oral inoculation with high doses of Go/Gd-like viruses resulted in the deaths of up to 50% of infected geese. Transmission from infected geese to chickens occurred only by fecal contact, whereas transmission to quail occurred by either aerosol or fecal spread. This difference is probably 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 hypothesis 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, especially quail, supports the wisdom of separating aquatic and land-based poultry in the markets in Hong Kong and the need for continued surveillance in the field and live-bird markets in which different types of poultry are in contact with one another.

FIG. 1.

Phylogenetic analysis of the HA1 genes of H5 influenza A viruses. The tree was generated with PAUP by using a maximum-parsimony algorithm. Nucleotides 77 through 1037 (961 bp) of the HA gene were analyzed. The tree is rooted to A/Japan/305/57 (H2N2). Only Eurasian lineages are shown. The lengths of the horizontal lines are proportional to the minimum numbers of nucleotide differences required to join nodes. Vertical lines are for spacing branches and labels. Abbreviations: Ck, chicken; Dk, duck; Env, environment; Gs, goose; Ty, turkey; GD, Guangdong; HK, Hong Kong.

FIG. 2.

Changes in the weights of mice infected with goose H5N1 influenza viruses. BALB/c mice were infected with Gs/HK/437-4/99 (⧫), Gs/HK/437-6/99 (•), Gs/HK/437-8/99 (▴), Gs/HK/437-10/99 (•), Gs/HK/485-3/00 (○), and Gs/HK/485-5/00 (□). Untreated animals (▵) received PBS. The weights of the mice were measured on days 0, 3, 5, 7, 9, 11, 14, and 16 after infection. Each value is the percent change in the initial mean starting weight on day 0. The standard errors (SE) are given.