Equine Sleeping Sickness Or Equine Encephalomyelitis

Equine Sleeping Sickness

What is it?
Equine sleeping sickness or equine encephalomyelitis is a virus that attacks the brain and central nervous system. The virus causes inflammation of the brain and spinal cord. This disease is also deadly for humans. There are two forms currently active in the United States: Eastern equine encephalomyelitis (EEE) and Western equine encephalomyelitis (WEE).

What are the symptoms?
Horses may lose their appetite, display excitable or compulsive behavior, and walk blindly into objects. The first apparent signs occur four to five days after infection. The horse will usually have a fever and rapid heart rate and show signs of anorexia, depression, and variable other neurological signs.

As equine sleeping sickness progresses, the brain stem and spinal cord are affected. Muscle weakness, behavioral changes and dementia occur. Other symptoms include aggression, head pressing, wall leaning, compulsive circling, and blindness. Surviving horses may suffer permanent damage. The reported mortality rate for EEE is 75-90 percent, and it's 20-50 percent for WEE.

Where does it come from?
Mosquitoes transmit the virus from small infected animals such as birds and rodents to horses. Outbreaks are more common during the warm, humid weather of the summer. Horses cannot transmit EEE or WEE to humans.

How is it diagnosed?
Diagnosis of EEE and WEE is based on the clinical signs and the occurrence of an epidermiologic pattern that relates to warm weather and mosquitoes. The diagnosis is confirmed by paired-sample blood serologic testing and postmortem examination of the brain and spinal cord.

How is it treated?
There is no specific treatment for viral encephalomyelitis. Anti-inflammatory and anticonvulsant drugs may be used. Antibiotics may be needed to treat secondary complications such as pneumonia. Supplemental fluids and feeding will prevent dehydration and malnutrition. Protect against falls for convulsions with heavy bedding as well as leg and head wraps. If the horse is unable to stand, slinging or propping may help.

How is it prevented?
Horses should be vaccinated annually against EEE and WEE before mosquito season begins. In areas where the mosquito season is very long or year-round, vaccines may need to be given twice a year. Vaccines may be single or combination vaccines. Three-way shots include protection from EEE, WEE and equine tetanus. Four way shots include protection against equine flu as well.

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