Objective—To determine signalment, clinical findings,
results of diagnostic testing, outcome, and postmortem
findings in horses with West Nile virus
Animals—46 horses with WNV encephalomyelitis.
Procedure—Clinical data were extracted from medical
records of affected horses.
Results—On the basis of clinical signs and results of
serologic testing, WNV encephalomyelitis was diagnosed
in 46 of 56 horses with CNS signs. Significantly
more males than females were affected. Increased
rectal temperature, weakness or ataxia, and muscle
fasciculations were the most common clinical signs.
Paresis was more common than ataxia, although both
could be asymmetrical and multifocal. Supportive
treatment included anti-inflammatory medications,
fluids, antimicrobials, and slinging of recumbent horses.
Results of the IgM capture ELISA and the plaque
reduction neutralization test provided a diagnosis in
43 horses, and only results of the plaque reduction
neutralization test were positive in 3 horses. Mortality
rate was 30%, and 71% of recumbent horses were
euthanatized. One horse that had received 2 vaccinations
for WNV developed the disease and was euthanatized.
Follow-up communications with 19 owners
revealed that most horses had residual deficits at 1
month after release from the hospital; abnormalities
were resolved in all but 2 horses by 12 months after
Conclusions and Clinical Relevance—Our findings
were similar to those of previous WNV outbreaks in
horses but provided additional clinical details from
monitored hospitalized horses. Diagnostic testing is
essential to diagnosis, treatment is supportive, and
recovery rate of discharged ambulatory horses is
< 100%. (J Am Vet Med Assoc 2003;222:1241–1247)