HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Kinney, R. M. Articles by Brault, A. C. Search for Related Content PubMed PubMed Citation Articles by Kinney, R. M. Articles by Brault, A. C. Agricola Articles by Kinney, R. M. Articles by Brault, A. C.

Avian virulence and thermostable replication of the North American strain of West Nile virus

Melissa C. Whiteman^1,

¹ Division of Vector-borne Infectious Diseases, National Center for Zoonotic, Vector-borne and Enteric Diseases, Coordinating Center for Infectious Diseases, Centers for Disease Control and Prevention, US Department of Health and Human Services, PO Box 2087, Fort Collins, CO 80522, USA
² Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80522, USA
³ Center for Vector-borne Diseases and Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA

Correspondence
Richard M. Kinney
rmk1{at}cdc.gov

The NY99 genotype of West Nile virus (WNV) introduced into North America has demonstrated high virulence for American crows (AMCRs), whilst a closely related WNV strain (KEN-3829) from Kenya exhibits substantially reduced virulence in AMCRs [Brault, A. C., Langevin, S. A., Bowen, R. A., Panella, N. A., Biggerstaff, B. J., Miller, B. R. & Nicholas, K. (2004). Emerg Infect Dis 10, 2161–2168]. Viruses rescued from infectious cDNA clones of both the NY99 and KEN-3829 strains demonstrated virulence comparable to that of their parental strains in AMCRs. To begin to define parameters that might explain the different virulence phenotypes between these two viruses, temperature-sensitivity assays were performed for both viruses at the high temperatures experienced in viraemic AMCRs. Growth curves of the two WNV strains were performed in African green monkey kidney (Vero; 37–42 °C) and duck embryonic fibroblast (DEF; 37–45 °C) cells cultured at temperatures that were tolerated by the cell line. Unlike the NY99 virus, marked decreases in KEN-3829 viral titres were detected between 36 and 120 h post-infection (p.i.) at temperatures above 43 °C. Replication of KEN-3829 viral RNA was reduced 6500-fold at 72 h p.i. in DEF cells incubated at 44 °C relative to levels of intracellular virus-specific RNA measured at 37 °C. In contrast, replication of virus derived from the NY99 infectious cDNA at 44 °C demonstrated only a 17-fold reduction in RNA level. These results indicated that the ability of WNV NY99 to replicate at the high temperatures measured in infected AMCRs could be an important factor leading to the increased avian virulence and emergence of this strain of WNV.

Present address: Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555-0606, USA.