Equine Encephalomyelitis, commonly known as Sleeping Sickness, is a rare but serious disease. Sleeping Sickness is caused by a virus that infects the central nervous system, consisting of the brain and spinal cord. Any horse of any age can be infected with the virus, although it is uncommon in horses under the age of three months.
There are three forms of the virus, two of which are significant in North America. The Eastern Equine Encephalitis (EEE) and Western Equine Encephalitis (WEE) have been found in Canada and the United States and the Venezuelan Equine Encephalitis (VEE) has been found in Central and South America. The virus is spread to horses from birds, small mammals and reptiles through mosquitoes. The spread requires sufficient host and carrier capabilities giving it a geographical and seasonal effect. Outbreaks are more likely to happen during the warm, humid weather of the summer months.
Equine Sleeping Sickness occurs when the virus enters the horse and causes inflammation of the brain and spinal cord. The most common clinical sign of infection is depression. The horse may develop a fever, lose their appetite and act colicy. They may also have trouble walking, start to move in circles, become blind and press their head into walls. The first apparent signs occur four to five days after infection. As Equine Sleeping Sickness progresses, the brain stem and spinal cord become more affected. Muscle weakness, behavioral changes and dementia occur. Other symptoms include aggression, wall leaning, compulsive circling, and blindness. Surviving horses may suffer permanent damage. The reported mortality rate for EEE is 75-90 percent, for WEE it is 20-50 percent. Some surviving patients will have residual and permanent neurological signs. There are many causes of central nervous system disease in the horse, including viral, bacterial, parasitic, developmental or traumatic disease and therefore all horses with the above mentioned signs need to be seen by a veterinarian.
Unfortunately, there is no specific treatment for horses suffering from Sleeping Sickness. Much of the treatment is aimed at general nursing care. Anti-inflammatories and anticonvulsants may be used to reduce the effects of the virus. Fluid therapy may be necessary to maintain hydration status of the animal. Protecting the animal from muscle problems following laying down for long periods of times may pose problems in many situations.
Equine Sleeping Sickness is a preventable disease. At Twin Valley VHS we recommend annual vaccination for both Eastern and Western Equine Encephalitis in all horses. These are included in our vaccines with a tetanus vaccine as well. Other diseases that should be vaccinated against include West Nile and Influenza. Other measures necessary to reduce infection include minimizing mosquito populations.
If you have any questions regarding the above information or any questions/concerns in general, please contact Twin Valley VHS at 745-6642.
Dr. Justin Noble DVM
Twin Valley Veterinary Health Services