Factors associated with West Nile virus disease fatalities in horses.
In 2003, the occurrence and location of horses with clinical signs of West Nile virus infection were identified in the southern portion of Saskatchewan with the help of veterinarians, owners, and the regional laboratory. A total of 133 clinical cases were reported between July 30 and September 19, 2003; however, postseason surveillance suggests that the number of cases was underestimated. The case fatality rate was 43.8% (95% CI 35.2, 52.4). Factors associated with fatality in clinical cases included sex, week of onset of clinical signs, and coat color. Reported clinical cases clustered within regional health authority districts, suggesting regional differences in geographic factors, potentially including climate and mosquito control, that could contribute to the risk of disease. However, most of the variation in the risk of fatality in clinical cases is explained at the individual level rather than the Regional Health Authority level, which suggests the outcome of clinical disease is primarily determined by characteristics of, or management factors affecting, the individual horse.
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan. tasha.epp@usask.ca
Tasha
T
Epp
Cheryl
C
Waldner
Keith
K
West
Hugh
H
Townsend
D000822:Animal Husbandry / Q000379:methods; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D001947:Breeding; D016000:Cluster Analysis; D005260:Female; D006734:Horse Diseases / Q000453:epidemiology / Q000401:mortality*; D006736:Horses; D008297:Male; D009032:Mosquito Control; D012307:Risk Factors; D012525:Saskatchewan / Q000453:epidemiology; D012621:Seasons; D016036:Seroepidemiologic Studies; D012737:Sex Factors; D014901:West Nile Fever / Q000453:epidemiology / Q000401:mortality / Q000662:veterinary*; D014902:West Nile virus / Q000276:immunology* / Q000302:isolation & purification
D000914:Antibodies, Viral