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Outcome of equids with clinical signs of West Nile virus infection and factors associated with death

Patricia Salazar DVM, MS1,2, Josie L. Traub-Dargatz DVM, MS, DACVIM3, Paul S. Morley DVM, PhD, DACVIM4, Delwin D. Wilmot DVM5, David J. Steffen DVM, PhD, DACVP6, Wayne E. Cunningham DVM7, and M. D. Salman BVMS, MPVM, PhD, DACVPM8
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  • 1 Animal Population Health Institute, Colorado State University, Fort Collins, CO 80523.
  • | 2 present address is Department of Clinical Sciences, Large Animal Surgery and Medicine, College of Veterinary Medicine, Auburn University, AL 36849.
  • | 3 Animal Population Health Institute, Colorado State University, Fort Collins, CO 80523.
  • | 4 Animal Population Health Institute, Colorado State University, Fort Collins, CO 80523.
  • | 5 Nebraska Department of Agriculture, Bureau of Animal Industry, Lincoln, NE 68509.
  • | 6 Veterinary Diagnostic Center, University of Nebraska, Lincoln, NE 68583.
  • | 7 Colorado Department of Agriculture, Division of Animal Industry, Lakewood, CO 80215.
  • | 8 Animal Population Health Institute, Colorado State University, Fort Collins, CO 80523.

Abstract

Objective—To determine outcome of equids in the western United States with clinical signs of West Nile virus (WNV) infection and identify factors associated with risk of death in infected equids.

Design—Cross-sectional study.

Animals—484 equids in Nebraska and Colorado.

Procedure—Owners of 484 equids with laboratoryconfirmed West Nile virus infection in Nebraska and Colorado were contacted by telephone, and a questionnaire was used to obtain information on signalment, management, clinical signs, date of disease onset, duration of disease, WNV vaccination status, and health status at the time of the interview.

Results—137 of 482 (28.4%) animals died or were euthanatized. Ataxia, lethargy, muscle fasciculations, and weakness were the most common clinical signs of disease. Animals ≥ 3 years old were more likely to die than were animals ≤ 2 years old. Unvaccinated equids were twice as likely to die as were animals that had been vaccinated at least once prior to the onset of disease. Animals that were recumbent and unable to rise were 78 times as likely to die as were animals that never lost the ability to rise. Females were 2.9 times as likely to die as males. Two hundred seventy-one of 339 (79.9%) animals that survived recovered fully; mean duration of disease for these animals was 22.3 days.

Conclusions and Clinical Relevance—Among equids with WNV infection, age, vaccination status, an inability to rise, and sex were associated with the risk of death. (J Am Vet Med Assoc 2004;225:267–274)

Abstract

Objective—To determine outcome of equids in the western United States with clinical signs of West Nile virus (WNV) infection and identify factors associated with risk of death in infected equids.

Design—Cross-sectional study.

Animals—484 equids in Nebraska and Colorado.

Procedure—Owners of 484 equids with laboratoryconfirmed West Nile virus infection in Nebraska and Colorado were contacted by telephone, and a questionnaire was used to obtain information on signalment, management, clinical signs, date of disease onset, duration of disease, WNV vaccination status, and health status at the time of the interview.

Results—137 of 482 (28.4%) animals died or were euthanatized. Ataxia, lethargy, muscle fasciculations, and weakness were the most common clinical signs of disease. Animals ≥ 3 years old were more likely to die than were animals ≤ 2 years old. Unvaccinated equids were twice as likely to die as were animals that had been vaccinated at least once prior to the onset of disease. Animals that were recumbent and unable to rise were 78 times as likely to die as were animals that never lost the ability to rise. Females were 2.9 times as likely to die as males. Two hundred seventy-one of 339 (79.9%) animals that survived recovered fully; mean duration of disease for these animals was 22.3 days.

Conclusions and Clinical Relevance—Among equids with WNV infection, age, vaccination status, an inability to rise, and sex were associated with the risk of death. (J Am Vet Med Assoc 2004;225:267–274)