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Journal of Virology, August 2007, p. 8515-8524, Vol. 81, No. 16
0022-538X/07/$08.00+0     doi:10.1128/JVI.00435-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Molecular Changes in the Polymerase Genes (PA and PB1) Associated with High Pathogenicity of H5N1 Influenza Virus in Mallard Ducks{triangledown}

D. J. Hulse-Post,1 J. Franks,1 K. Boyd,2 R. Salomon,1 E. Hoffmann,1 H. L. Yen,1 R. J. Webby,1 D. Walker,1 T. D. Nguyen,3 and R. G. Webster1*

St. Jude Children's Research Hospital, Department of Infectious Diseases, Division of Virology, Memphis, Tennessee,1 St. Jude Children's Research Hospital, Animal Resources Center, Memphis, Tennessee,2 Department of Virology, National Institute of Veterinary Research, Ministry of Agriculture and Rural Development, Hanoi, Vietnam3

Received 28 February 2007/ Accepted 23 May 2007

The highly pathogenic (HP) influenza viruses H5 and H7 are usually nonpathogenic in mallard ducks. However, the currently circulating HP H5N1 viruses acquired a different phenotype and are able to cause mortality in mallards. To establish the molecular basis of this phenotype, we cloned the human A/Vietnam/1203/04 (H5N1) influenza virus isolate that is highly pathogenic in ferrets, mice, and mallards and found it to be a heterogeneous mixture. Large-plaque isolates were highly pathogenic to ducks, mice, and ferrets, whereas small-plaque isolates were nonpathogenic in these species. Sequence analysis of the entire genome revealed that the small-plaque and the large-plaque isolates differed in the coding of five amino acids. There were two differences in the hemagglutinin (HA) gene (K52T and A544V), one in the PA gene (T515A), and two in the PB1 gene (K207R and Y436H). We inserted the amino acid changes into the wild-type reverse genetic virus construct to assess their effects on pathogenicity in vivo. The HA gene mutations and the PB1 gene K207R mutation did not alter the HP phenotype of the large-plaque virus, whereas constructs with the PA (T515A) and PB1 (Y436H) gene mutations were nonpathogenic in orally inoculated ducks. The PB1 (Y436H) construct was not efficiently transmitted in ducks, whereas the PA (T515A) construct replicated as well as the wild-type virus did and was transmitted efficiently. These results show that the PA and PB1 genes of HP H5N1 influenza viruses are associated with lethality in ducks. The mechanisms of lethality and the perpetuation of this lethal phenotype in ducks in nature remain to be determined.


* Corresponding author. Mailing address: Division of Virology, Department of Infectious Diseases, Mail Stop 330, St. Jude Children's Research Hospital, 332 N. Lauderdale St., Memphis, TN 38105-2794. Phone: (901) 495-3400. Fax: (901) 523-2622. E-mail: Robert.webster{at}stjude.org

{triangledown} Published ahead of print on 6 June 2007.


Journal of Virology, August 2007, p. 8515-8524, Vol. 81, No. 16
0022-538X/07/$08.00+0     doi:10.1128/JVI.00435-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.




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