Viral Equine Encephalomyelitis (Meningoencephalitis)
There are three well known types of viral encephalomyelitis, Eastern Equine Encephalomyelitis (EEE), Western Equine Encephalomyelitis (WEE) and Venezuelan Equine Encephalomyelitis (VEE). West Nile Virus is also a viral encephalomyelitis but will discussed separately.
All three types are caused by
from the family alphavirus . Viral subtypes are
seen within each type of encephalomyelitis.
Rodents, reptiles and birds are considered reservoirs of these viruses, though they show no clinical signs of disease. Transmission of the virus from one of the reservoir animals to the horse occurs through biting insects most notably the . The virus is introduced into the horse’s blood through an insect bite. The virus travels through the blood toward the central nervous tissue. The virus is , meaning it has a preference for nervous tissue, especially the matter. Once inside the central nervous system the virus infects the nerve cells and the cells of the meninges causing inflammation. Diffuse inflammation of the meninges and the grey matter is called meningoencephalomyelitis. The predispositions are young and those who are unvaccinated and kept in pastures during peak mosquito season. EEE is most prevalent in the southeastern states, WEE in the western states and VEE in Mexico, Columbia & Venezuela. In the acute stage of disease, the horse shows general signs of infection. These include fever, depression and anorexia. Approximately five days after infection the horse begins to show signs of infection of the central nervous system. These signs include head pressing, wandering, circling, dementia, aggression, excitability, ataxia, blindness, cranial nerve impairment, paresis, recumbency, seizure, coma and death.
Diagnosis of viral encephalomyelitis can be made through serology, and analysis of the CSF.
Treatment is generally supportive, including IV fluids, NSAID’s, DMSO, antiviral medications, nasogastric feeding tube, catheters, and slings. Prognosis depends on the type and severity of the infection. Mortality rates for EEE is 70-90%, WEE is 20-30% and VEE is 40-90%. Full recovery is rare. Most animals that do recover have lasting impairment due to damage of tissue during acute infection. All three types of viral encephalomyelitis can be prevented through . It is recommended that horses be vaccinated annually at least three weeks before the start of mosquito season.
230
Made with FlippingBook Publishing Software