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United States Department of Agriculture

Agricultural Research Service

Research Project: APPLICATION OF BIOLOGICAL AND MOLECULAR TECHNIQUES TO THE DIAGNOSIS AND CONTROL OF AVIAN INFLUENZA AND OTHER EMERGING POULTRY PATHOGENS Title: The effect of NS1 gene exchange on the pathogenicity of H5N1 HPAI viruses in ducks

Authors
item Sarmento, Luciana
item Wasilenko, Jamie
item Pantin-Jackwood, Mary

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 2009
Publication Date: March 15, 2010
Citation: Sarmento, L., Wasilenko, J.L., Pantin Jackwood, M.J. 2010. The effects of NS gene exchange on the pathogenicity of H5N1 HPAI viruses in ducks. Avian Diseases. 54:532-537.

Interpretive Summary: Avian influenza viruses cause severe disease in poultry. Ducks and wild aquatic birds are the natural reservoir of all influenza viruses. Until 2002, highly pathogenic avian influenza (HPAI) viruses of the H5N1 type caused only mild respiratory infections in ducks. Since then, new viruses have emerged that can cause high mortality in ducks and other waterfowl. In order to understand why this increase in pathogenicity is occurring, we used reverse genetics to make viruses that differed only in their NS1 (non structural 1) protein. The NS1 protein is known to suppress immune responses in influenza virus-infected hosts affecting virus pathogenesis. Exchanging the NS genes from A/Ck/HK/220/97 (a virus that produces mild disease in ducks) and A/Dk/VN/201/05 (a very virulent virus for ducks) in the rEgret/02 virus (a recombinant virus derived from A/Egret/HK/757.2/02), resulted in differences in time of death between the viruses. However, the exchange of this particular gene was not enough to induce complete change in pathogenicity of the parent virus. Infection with the recombinant viruses affected the expression of immune related genes in spleens and lungs when compared to controls, but when compared among them, the expression of the duck genes was similar. Furthermore, amount of virus in the tissues of the ducks were similar in ducks infected with the recombinant viruses. In conclusion, under these experimental conditions, exchanging NS had minimal effect on the virus pathogenicity, and suggests that other viral genes are most likely contributing to the increased virulence of H5N1 HPAI viruses in ducks.

Technical Abstract: Until 2002, H5N1 highly pathogenic avian influenza (HPAI) viruses caused only mild respiratory infections in ducks. Since then, new viruses have emerged that cause systemic disease and high mortality in ducks and other waterfowl. Studies on HPAI virus pathogenicity in ducks have been limited and there is no clear explanation of why the pathogenicity of some H5N1 HPAI viruses has increased. The NS1 protein is known to suppress immune responses in influenza virus-infected hosts affecting virus pathogenesis. In order to determine if the NS1 protein contributes to increased virulence in ducks, single gene reassortant viruses were generated. Exchanging the NS (non-structural) genes from A/Ck/HK/220/97 (a virus that produces mild disease in ducks) and A/Dk/VN/201/05 (a very virulent virus for ducks) in the rEgret/02 background (a recombinant virus derived from A/Egret/HK/757.2/02), resulted in differences in mean death times (MDTs) compared to infection with the rEgret/02 virus in ducks. However, the exchange of this particular gene was not enough to induce complete change in pathogenicity of the parent virus. Infection with the recombinant viruses affected the expression of immune related genes in spleens and lungs when compared to controls, but when compared among them, the expression of the duck genes was similar. Furthermore, virus titers in spleen, lung and brain and antigen distribution in various tissues were similar in ducks infected with the recombinant viruses. All together these data show that, under these experimental conditions, exchanging NS had minimal effect on the virus pathogenicity, and suggest that other viral genes are most likely contributing to the increased virulence of H5N1 HPAI viruses in ducks.

Last Modified: 11/25/2014
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