Submitted to: Research Conference on Orthomyxoviruses
Publication Type: Abstract Only
Publication Acceptance Date: 6/13/2005
Publication Date: 7/28/2005
Citation: Pantin Jackwood, M.J., Swayne, D.E., Suarez, D.L., Beck, J.R., Spackman, E. 2005. Pathogenicity of four different H5N1 avian influenza viruses in ducks [abstract]. Research Conference on Orthomyxoviruses p.47.
Technical Abstract: Ducks and other wild aquatic birds are the natural reservoir of influenza type A viruses. Until recently, none of the highly pathogenic H5N1 viruses had been shown to produce disease in ducks. However, in 2002 a pathogenic H5N1 outbreak among waterfowl and wild birds occurred in Hong Kong causing the death of many resident avian species. In order to assess the pathogenicity and transmission potential in ducks of these new viruses, we studied the clinical disease, gross and histologic lesions, and distribution of viral antigen in 2-week-old white Pekin ducks inoculated intranasally with one of four Asian origin H5N1 highly pathogenic Avian Influenza (HPAI) viruses. The viruses examined were: A/Vietnam/1203/04 and A/Prachinbury/6231/04, isolated from human cases of HPAI in Vietnam and Thailand respectively, and A/Crow/Thailand/04 and A/Egret/HK/757.2/02. Ducks inoculated with A/Vietnam/1203/04, A/Crow/Thailand/04 and A/Egret/HK/757.2/02 developed acute disease, including severe neurological dysfunction and death. A/Vietnam/1203/04 and A/Egret/HK/757.2/02 killed 7 out of 8 ducks within 10 days, and A/Crow/Thailand/04 killed 8 out of 8, with a median death time (MDT) for all viruses between 4.1- 4.5 days after inoculation. Grossly, the birds were dehydrated. Small thymus, splenomegly, and ischemic necrosis of beak and toes were observed. Histologic lesions were present in multiple organs and consisted mostly of necrosis and inflammation. The brain, lungs, heart, pancreas, skeletal muscle, and adrenal glands were the most consistently affected and viral antigen was most often detected by immunohistochemistry in the parenchyma of these organs. A/Prachinbury/6231/04 killed 3 out of 8 ducks within 10 days, producing mild depression and affecting body weight gain, but not inducing neurological signs. The MDT was 6.3 days and gross lesions consisted mostly of enlarged and flaccid heart and serous exudates in body cavities. All four viruses studied were isolated from oropharyngeal and cloacal swabs, with mean viral titers between 3.7 and 5.8 log10EID50/ml and 1.36 and 2.36 log10EID50/ml respectively at 3 days post inoculation (dpi). Viruses were also isolated from brain, heart, lung and muscle tissues collected at 2 dpi. Contact birds introduced 2 days after inoculating the initial group also got infected and died demonstrating efficient transmission for all the viruses studied. These results confirm that some of the circulating H5N1 isolates are capable of causing disease in ducks, with three of the four isolates studied inducing severe neurological signs. Consequences of this change in pathogenicity and its role in the transmission and evolution of HPAI will need to be further evaluated.