title: Avian virulence and thermostable replication of the North American strain of West Nile virus.
abstract: 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 degrees C) and duck embryonic fibroblast (DEF; 37-45 degrees 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 degrees C. Replication of KEN-3829 viral RNA was reduced 6500-fold at 72 h p.i. in DEF cells incubated at 44 degrees C relative to levels of intracellular virus-specific RNA measured at 37 degrees C. In contrast, replication of virus derived from the NY99 infectious cDNA at 44 degrees 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.
authors.affiliation: 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.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Kinney
authors.affiliation: 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.
authors.forename: Claire Y-H
authors.initials: CY
authors.lastname: Huang
authors.affiliation: 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.
authors.forename: Melissa C
authors.initials: MC
authors.lastname: Whiteman
authors.affiliation: Department of Biomedical Sciences, Colorado State University, Fort Collins, CO 80522, USA.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Bowen
authors.affiliation: Center for Vector-borne Diseases and Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
authors.forename: Stanley A
authors.initials: SA
authors.lastname: Langevin
authors.affiliation: 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.
authors.forename: Barry R
authors.initials: BR
authors.lastname: Miller
authors.affiliation: Center for Vector-borne Diseases and Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
authors.forename: Aaron C
authors.initials: AC
authors.lastname: Brault
mesh_terms: D000818:Animals; D001715:Bird Diseases / Q000821:virology*; D001831:Body Temperature; D002460:Cell Line; D002522:Chlorocebus aethiops; D046368:Crows / Q000821:virology*; D004372:Ducks; D012367:RNA, Viral / Q000096:biosynthesis; D016019:Survival Analysis; D013696:Temperature; D014709:Vero Cells; D010948:Viral Plaque Assay; D014774:Virulence; D014779:Virus Replication; D014901:West Nile Fever / Q000662:veterinary* / Q000821:virology; D014902:West Nile virus / Q000472:pathogenicity* / Q000502:physiology*
chemical_list: D012367:RNA, Viral