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Introduction West Nile virus (WNV) is a mosquito-borne zoonotic pathogen and more than 20 years after its introduction in North America is still a major cause of disease in horses. 1 , 2 It caused 842 confirmed clinical cases in horses

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in Journal of the American Veterinary Medical Association

West Nile virus was first identified in Africa in 1937, and subsequently, Africa, Europe, Australia, and Asia were recognized as regions in which the virus was endemic. 1 In 1999, concurrent outbreaks of encephalitis among crows, humans, and

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in Journal of the American Veterinary Medical Association

West Nile virus is a single-stranded RNA virus of the family Flaviviridae that has been endemic in North America since 1999. 1 It is maintained in an enzootic cycle between avian and mosquito hosts, with Culex mosquitoes being the primary

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in American Journal of Veterinary Research

West Nile virus is a flavivirus endemic in many areas of Africa, western Asia, the Middle East, and, most recently, the United States. It is a vector-borne infection maintained in nature by a mosquito-bird cycle. 1 In humans and horses, WNV

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in American Journal of Veterinary Research

West Nile virus is a flavivirus of the Japanese encephalitis antigen complex that has been associated with considerable death rates among various species of birds of prey since its introduction to North America in 1999. 1–7 Birds are the natural

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in Journal of the American Veterinary Medical Association

West Nile virus-related deaths among birds were first noted during the summer of 1999 in New York City, and over the next several years, such deaths spread rapidly across North America. 1,2 In addition to being the cause of death in countless

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in American Journal of Veterinary Research

West Nile virus is a vector-borne flavivirus that was historically endemic to Africa, West Asia, and the Middle East. West Nile virus was first recognized to cause disease within the United States in equids, birds, and humans in New York in 1999

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine signalment, clinical findings, results of diagnostic testing, outcome, and postmortem findings in horses with West Nile virus (WNV) encephalomyelitis.

Design—Retrospective study.

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 release.

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)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate CSF in horses with confirmed West Nile virus encephalomyelitis.

Design—Retrospective study.

Animals—30 horses.

Procedure—Results of CSF analyses from horses with acute neurologic signs attributed to West Nile virus infection that was confirmed by immunoglobulin M antibody capture ELISA were reviewed and analyzed.

Results—Among 30 CSF samples, findings in 8 (27%) were within reference ranges and in 22 (73%) were abnormal. Among the 22 abnormal samples, mononuclear pleocytosis was found in 16 (73%) and high protein concentration with nucleated cell count within reference range was found in 6 (27%) samples. A predominance of lymphocytes was found in 11 of 16 samples with mononuclear pleocytosis, and a predominance of large mononuclear cells was found in 5 of 16 samples. Sensitivities of analyses of CSF obtained from the lumbosacral and atlanto-occipital regions of the spinal cord were 89 and 50%, respectively.

Conclusions and Clinical Relevance—Results suggest that in horses with acute onset of neurologic signs caused by West Nile virus encephalomyelitis, findings in the CSF are likely to be abnormal, mononuclear pleocytosis with lymphocytic predominance may be most commonly observed, and CSF collected from the lumbosacral region may be abnormal more commonly than CSF collected from the atlanto-occipital region. (J Am Vet Med Assoc 2002;221:1303–1305)

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in Journal of the American Veterinary Medical Association

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)

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in Journal of the American Veterinary Medical Association