Objective—To describe the prevalence of West Nile virus (WNV) infection and evaluate factors associated with positive IgM capture ELISA results in equids with clinical signs compatible with WNV infection.
Design—Retrospective case series.
Sample Population—Laboratory submission forms from 1,104 equids tested for WNV in Colorado in 2003.
Procedures—Submission forms accompanying samples submitted for detection of WNV via IgM capture ELISA were obtained from the Colorado state veterinarian and diagnostic laboratories performing the tests. Data on signalment, clinical signs, history of vaccination against WNV, and assay results were collected from laboratory submission forms. Equids with clinical signs compatible with WNV infection in which IgM capture ELISA results were positive were considered as case equids.
Results—1,104 equids were tested for WNV; 1,017 (92.1%) had clinical signs compatible with WNV infection. Among equids with clinical signs compatible with WNV infection, the odds of testing positive for WNV via IgM capture ELISA were lower in males and in vaccinated equids and higher in equids with moderate and severe illness, compared with females, unvaccinated equids, and equids with mild illness.
Conclusions and Clinical Relevance—Among equids with clinical signs compatible with WNV infection, vaccination against WNV, severity of clinical signs, duration of illness, and region in Colorado were associated with increased risk of having a positive IgM capture ELISA result.
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.
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)