Equine encephalomyelitis

EQUINE ENCEPHALOMYELITIS

Synonym

  • Blind staggers

Definition

  • A serious disease of equine caused by arbovirus characterised by signs of central nervous system

Aetiology

  • Arbovirus - There are many strains of the virus
  • Eastern strain
  • Western strain
  • Venezuelan strain

Susceptibility

  • Horses, mules
  • Man and birds can be infected

Transmission

  • Mosquitoes, birds, reptiles ,rodents act as reservoirs
  • Western strain of the virus infects variety of birds and is transmitted by Culex mosquitoes
  • Eastern strain also infects birds but uses Aedes mosquitoes which transmits the disease to horses
  • Seasonal occurrence

Pathogenesis

  • From the bite of the insect, virus enters into the bood giving rise to viremia
  • Viremia is transient in the American disease ( Eastern and Western strains) while it is persistent in Venezuelan strain
  • Virus is found in the saliva and nasal discharge
  • The virus enters into the brain through blood and affects neurons producing the symptoms.

Clinical signs

  • Affected horses lose awareness of the surroundings, wander aimlessly
  • Unresponsive to commands
  • Strike violently against objects like fence etc.
  • Initial pyrexia and malaise
  • Excitement, restlessness, mania
  • Blind, move in circles
  • Muscular tremors
  • Paralysis- Stupor, head hanging
  • Fall down/ unable to get up
  • Complete cessation of feeding, micturition and defecation
  • Subnormal temperature- Death

Gross lesions

  • Hyperaemia and edema of brain and spinal cord
  • Enlarged oedematous lymphnodes

Microscopic lesions

  • Degenerative changes in liver and kidney
  • Brain- disseminated non suppurative encephalitis
  • Cortex, thalamus and hypothalamus revealed tigrolysis, chromatolysis, karyorrhexis, gliosis, accumulation of lymphocytes and neutrophils around the neurons- Neuronophagia
  • Leucocytes and glial cells form nodules around injured neurons
  • Grey matter is infiltrated with leucocytes
  • Perivascular cuffing in grey matter and extending into white matter
  • Vasculitis of spinal cord

Diagnosis

  • Symptoms and lesions in brain
  • Brain from affected animal- injected subcutaneously or intra cerebrally or intra peritoneally in guinea pigs causes signs of paralysis in 3-5 days
  • Inoculation into chick embryos causes death in 18-24 hr
  • Complement fixation test
  • Neutralization test
Last modified: Monday, 19 March 2012, 8:27 AM