Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 8, 2008
Publication Date: June 16, 2008
Citation: Pantin Jackwood, M.J., Suarez, D.L. 2008. Pathogenicity of H5N1 HPAI viruses from Vietnam in chickens and ducks [abstract]. Workshop on Avian Influenza: Research to Policy, June 16-18, 2008, Hanoi, Vietnam. 2008 CDROM. Technical Abstract: Ducks and other wild aquatic birds are the natural reservoir of influenza type A viruses, and influenza viruses in these species normally is an asymptomatic infection. Even the viruses that are highly pathogenic for chickens typically can infect but do not cause disease in domestic ducks. However, with the goose/Guangdong/96 H5N1 lineage of HPAI virus, we have seen large changes in how this lineage of virus infects and causes disease in ducks. The Asian H5N1 highly pathogenic avian influenza (HPAI) viruses have changed from producing a mild respiratory or enteric infection in ducks to some strains causing systemic disease and death. Vietnam has been one of the countries most affected by H5N1 HPAI in Southeast Asia, with outbreaks persistently occurring in domestic ducks and chickens. Ducks, which make up a large part of poultry in Vietnam, have been recognized as one of the primary factors in the spread of AI this country. H5N1 viruses isolated in Vietnam in 2005 and 2007, were biologically characterized in both chickens and ducks. Based on the HA gene sequence, these viruses belong to clade 1 or clade 2, with these second group of viruses clustering in two distinct sublineages. All viruses were highly virulent not only in chickens, killing them within two days of experimental inoculation, but also in two-week old Pekin ducks, causing 100% mortality within four days of challenge. A marked increased in pathogenicity in ducks was observed with these viruses when compared to earlier H5N1 isolates from Vietnam and other countries. This increase in pathogenicity is the consequence of an increase in viral replication in tissues and an expanded tissue tropism. Field observations coincide with these results, with higher numbers of cases of H5N1 HPAI among domestic ducks, with high mortality, reported in Vietnam during the last years. Changes in pathogenicity of circulating viruses have important implications on the epidemiology of the virus and control methods.