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Equis ISSN 2398-2977

Western Equine Encephalomyelitis

Synonym(s): WEE, sleeping sickness

Contributor(s): Frank Andrews, Sarah Binns

Introduction

  • Non-supprative viral encephalitis of horses, birds and humans that is transmitted by mosquitoes (Culex tarsalisandCuliseta melanura)   Equine viral encephalitides  .
  • The virus is maintained in sylvatic populations of wild birds.
  • Cause: virus from:
    • Family:Togaviridae.
    • Genus:Alphaviridae.
    • Group A Arboviruses (closely related EEE   Eastern Equine Encephalomyelitis virus   and VEE viruses). Transmitted from sylvatic populations of wild brids to hroses via blood meal from mosquito bite. Virus over winters in other mammals, birds, amphibians and reptiles (reservoir hosts).
  • Signs: biphasic fever (38-41°C, 2 and 6 days), then general depression, dullness, anorexia, stiffness, ataxia, hyperesthesia, aggression, excitability, continuous chewing movements, aimless wandering, somnolence   →   head pressing, circling, twitching, recumbency and death.
  • Diagnosis: paired serum titers (4-fold increase in titer over 2-4 weeks), virus isolation from brain tissue at necropsy or single high serum titer during the acute phase of the disease.
  • Treatment: no specific antiviral treatment is available to treat WEE.  Therefore, supportive care, nursing care, prevention of self-trauma, and non-steroidal anti-inflammatory therapy, fluids, electrolytes, total and partial parental nutrition, DMSO and corticosteroids (controversial). Also, diazepam or phenobarbital to control convulsions.
  • Prognosis: guarded as mortality rates range from 10-50% in cases with neurologic signs.  Once recumbent, death may occur within 5 days.  Horses that recover from clinical disease frequently have persistent neurologic deficits. 

Pathogenesis

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Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

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