Submitted to: United States Animal Health Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 27, 2006
Publication Date: July 1, 2007
Citation: Pantin Jackwood, M.J., Suarez, D.L., Swayne, D.E. 2006. Increased pathogenicity of H5N1 Vietnam viruses in ducks. Proceedings of the 110th United States Animal Health Association Meeting, October 2006, Minneapolis, Minnesota. p. 93. Technical Abstract: Ducks and other wild aquatic birds are the natural reservoir of influenza type A viruses, which usually are nonpathogenic in these birds. The Asian H5N1 HPAI viruses have changed from producing a mild respiratory infection in ducks to some strains causing systemic disease and death. In order to further understand the change in pathogenicity of these new viruses in ducks, we studied the clinical disease, gross and microscopic lesions, and the tissue distribution of viral antigen in 2-week-old white Pekin ducks inoculated intranasally with two different strains of Asian origin H5N1 HPAI viruses isolated from ducks in Vietnam during 2006: A/duck/Vietnam-Ninh Binh/203/2006 and A/duck/Vietnam-Nam Dinh/218/2006. Ducks inoculated with these viruses were severely depressed the day after inoculation and presented neurological signs including tremors, uncontrollable shaking, marked loss of balance, tilted head, seizures, and paralysis. All ducks died, with a mean death time (MDT) of 3.3 days for ducks inoculated with A/duck/VN-Ninh Binh/203/2006 and 2.7 days for ducks inoculated with A/duck/Vietnam-Nam Dinh/218/2006. These ducks died more than a day earlier than ducks inoculated with an H5N1 Vietnam strain from 2004 (A/Vietnam/1203/04) or with any other previously studied Asian H5N1 virus. Grossly, dehydration, empty intestines, thymus atrophy and splenomegaly was observed in most ducks. In some ducks, congested and malacic brain, impacted proventriculus and gizzard full with intense bile staining of the mucosa, and pale pancreas, was also observed. Microscopically, the brain, heart, pancreas, skeletal muscle, and adrenal glands were the organs most consistently affected and viral antigen was most often detected in the parenchyma of these organs. Both viruses studied were isolated in high titers from oropharyngeal and cloacal swabs and also from brain, heart, spleen, lung and muscle tissues collected at 2 days post-inoculation. These viruses are more pathogenic to ducks than previously studied AI strains, this pathogenicity is related to increased viral replication in tissues.