Century Equine

Eastern and Western Encephalitis are mosquito borne diseases. Their names are indicative of their typical distribution (though this can vary). Birds and rodents are natural reservoirs for the disease. Mosquitoes then transfer the disease to other species, humans included. Horses are not able to transmit the disease as the virus does not reach the level needed in their blood stream for a mosquito to acquire it. Western Encephalitis has the lowest level of mortality (~50%) while mortality can approach 90% for Eastern Encephalitis. Risk varies from year to year depending on the distribution of birds/rodents and mosquitoes.

Symptoms can be difficult to appreciate initially. Horses may have a transient, mild to severe fever (103-106F) that can last 1-2 days. You may also see poor appetite. From here, your horse will begin to show neurological deficiencies. These include depression, somnolence, uncontrolled excitement after stimulation and more. Eventually horses may begin head pressing, acquire a head tilt and begin to exhibit muscle twitching. They may also lose the ability to pass manure and urinate normally. If recumbent and unable to stand, a horse’s prognosis is quite poor. Neurological symptoms are secondary to inflammation of the brain and spinal cord.

Treatment of these diseases is completely symptomatic. Diagnostic tests can be performed to confirm infection. Treatment can involve placement of IV and urinary catheters, drugs to decrease inflammation and other nursing care. Treatment may be necessary for weeks and if a horse survives the infection, it may have permanent neurological deficits.

Eastern and Western Encephalitis are diseases that are preventable with vaccination. These are consider core vaccines by the AAEP due to the severity of disease.