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Title: Comparison of the pathogenicity of different H5N1 HPAI viruses in chickens and ducks

Author
item Pantin Jackwood, Mary
item Kapczynski, Darrell
item Wasilenko, Jamie
item Sarmento, Luciana

Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Proceedings
Publication Acceptance Date: 6/25/2007
Publication Date: 10/18/2007
Citation: Pantin Jackwood, M.J., Kapczynski, D.R., Wasilenko, J.L., Sarmento, L. 2007. Comparison of the pathogenicity of different H5N1 HPAI viruses in chickens and ducks. In: Proceedings of theAmerican Association of Veterinary Laboratory Diagnosticians 50th Annual Conference, October 18-24, 2007, Reno, Nevada. p.125.

Interpretive Summary: In order to better understand the differences observed between chickens and ducks in their response to infection with Highly Pathogenic Avian Influenza (HPAI) viruses, we infected 2-week-old white ducks and chickens with four different strains of Asian origin H5N1 HPAI viruses: A/Ck/HK/220/97, A/Egret/HK/757.2/02, A/Ck/Indonesia/7/03 and A/duck/Vietnam /203/05, and studied the clinical disease, gross and microscopic lesions, and viral replication in these birds. Chickens infected with all four of these viruses were severely depressed and died in less than 2 days. None of the ducks infected with A/Ck/HK/220/97 died, contrary to all ducks infected with A/Egret/HK/757.2/02 or A/duck/Vietnam /203/05 which died in less than 6 six days. Six of ten ducks inoculated with A/ Ck/Indonesia/7/03 died. Sick ducks were depressed and also presented neurological signs. The severity of the lesions correlated with the level of viral replication in tissues. Lesions in the lung were more severe in chickens, and virus replication was observed in vascular endothelial cells which were not observed in the ducks. These differences may explain in part the differences in pathogenicity observed between the chickens and the ducks when inoculated with the same viruses. Differences in body temperature after infection were also observed between chickens and ducks, as also different cytokine expression in affected tissues, indicating differences in innate immune response. Understanding the mechanisms for cytokine induction and suppression following HPAI infection will provide insights into the pathogenicity of AIV in different avian species.

Technical Abstract: Contrary to what is observed in chickens where infection with highly pathogenic avian influenza (HPAI) viruses produce fatal disease, the Asian H5N1 HPAI viruses have changed from producing mild respiratory infections in ducks to some strains causing systemic disease and death. In order to further understand the difference in pathogenicity observed between chickens and ducks in their response to infection with H5N1 HPAI viruses, we studied the clinical disease, gross and microscopic lesions, the tissue distribution of viral antigen, and the cytokine profile in 2-week-old white Pekin ducks and White Leghorn chickens inoculated intranasally with four different strains of Asian origin H5N1 HPAI viruses: A/Ck/HK/220/97, A/Egret/HK/757.2/02, A/Ck/Indonesia/7/03, and A/duck/Vietnam /203/05. Chickens inoculated with all four of these viruses were severely depressed the day after inoculation and died with a mean death time (MDT) between 1.6 and 2 days post inoculation (dpi). None of the ducks inoculated with A/Ck/HK/220/97 died, contrary to all ducks inoculated with A/Egret/HK/757.2/02 or A/duck/Vietnam /203/05 which died, with MDT’s of 5.5 and 3.9 dpi respectively. Six of ten ducks inoculated with A/ Ck/Indonesia/7/03 died. Sick ducks were depressed and presented neurological signs. Microscopically, lesions and presence of viral antigen in tissues was similar in all the infected chickens and the ducks infected with A/Egret/HK/757.2/02, A/Ck/Indonesia/7/03, and A/duck/Vietnam/203/05, the severity of the lesions correlating with viral replication in tissues. Lesions in the lung were more severe in chickens, and virus replication was observed in vascular endothelial cells which were not observed in the ducks. These differences may explain in part the differences in pathogenicity observed between the chickens and the ducks when inoculated with the same viruses. No difference in body temperature was found between control chickens and chickens inoculated with any of the four viruses. Conversely, an increase in body temperature was observed in the ducks infected with A/Egret/HK/757.2/02, A/Ck/Indonesia/7/03, and A/duck/Vietnam /203/05, and this increase was proportional to virulence of the virus. Innate responses differed also between chickens and ducks. In general, cytokine expression in chickens was suppressed following infection when compared to controls. Understanding the mechanisms for cytokine induction and suppression following HPAI infection will provide insights into the pathogenicity of AIV in different avian species.