Equine encephalomyelitis, also called "sleeping sickness," is an infectious viral disease transmitted by mosquito bites that affects the central nervous system of the horse. Causative agents include the Eastern, Western, and Venezuelan Equine Encephalomyelitis viruses. The mortality of the three strains runs from moderate to high. The eastern strain occurs more frequently in the United States and has the highest mortality rate. These are zoonotic disases, which means that they can be transmitted to humans.

Clinical Signs

• Fever and depression
• Loss of appetite
• Overall drowsy appearance and no desire to move
• Self-mutilation, hyperexcitability, irritability, and a refusal of food and water
• Central nervous system signs of incoordination, head pressing, circling, sawhorse stance, circling, paddling motion of the limbs, paralysis, convulsions, and coma
• Irritability and aggressiveness towards handlers
• Blindness
• Abnormal sensitivity to light and sound
• Death two to three days after the first signs appear

Treatment

Treatment is mainly supportive, including fluid therapy, and the prudent administration of anti-inflammatory agents and anticonvulsants. The horse should be kept in a shaded, well-padded area. Mortality rate is high.

Prevention

Vaccination and mosquito control are recommended for prevention.

For more information, see Encephalomyelitis in horses.