Equine encephalomyelitis
Synonym
Definition
Aetiology
Susceptibility
Transmission
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Mosquitoes, birds, reptiles ,rodents act as reservoirs
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Western strain of the virus infects variety of birds and is transmitted by Culex mosquitoes
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Eastern strain also infects birds but uses Aedes mosquitoes which transmits the disease to horses
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Seasonal occurrence
Pathogenesis
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From the bite of the insect, virus enters into the bood giving rise to viremia
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Viremia is transient in the American disease ( Eastern and Western strains) while it is persistent in Venezuelan strain
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Virus is found in the saliva and nasal discharge
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The virus enters into the brain through blood and affects neurons producing the symptoms.
Clinical signs
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Affected horses lose awareness of the surroundings, wander aimlessly
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Unresponsive to commands
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Strike violently against objects like fence etc.
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Initial pyrexia and malaise
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Excitement, restlessness, mania
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Blind, move in circles
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Muscular tremors
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Paralysis- Stupor, head hanging
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Fall down/ unable to get up
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Complete cessation of feeding, micturition and defecation
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Subnormal temperature- Death
Gross lesions
Microscopic lesions
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Degenerative changes in liver and kidney
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Brain- disseminated non suppurative encephalitis
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Cortex, thalamus and hypothalamus revealed tigrolysis, chromatolysis, karyorrhexis, gliosis, accumulation of lymphocytes and neutrophils around the neurons- Neuronophagia
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Leucocytes and glial cells form nodules around injured neurons
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Grey matter is infiltrated with leucocytes
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Perivascular cuffing in grey matter and extending into white matter
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Vasculitis of spinal cord
Diagnosis
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Brain from affected animal- injected subcutaneously or intra cerebrally or intra peritoneally in guinea pigs causes signs of paralysis in 3-5 days
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Inoculation into chick embryos causes death in 18-24 hr
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Complement fixation test
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Neutralization test
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Last modified: Monday, 19 March 2012, 8:27 AM