Equine encephalomyelitis

Encephalomyelitis or inflammation of the brain tissue and the spinal cord, can be brought about by different viruses. Eastern-, Western- and Venezuelan equine encephalomyelitis (EEE, WEE and VEE) are viral encephalomyelitis of horses and human caused by arthropod borne viruses of genus Alphavirus of Togaviridae family and are characterized by fever, anorexia, depression and somnolence. The virus is transmitted by mosquitoes. As the name suggests, EEE is generally reported to Eastern coast of America. WEE is generally reported from Colorado, Kansas, California, Texas and Florida. VEE is generally reported from South America (Venezuela, Colombia) and in Central America.

Clinical signs: After an incubation period of 5-14 days, there may be fever and horse appears sleepy, dull and unwilling to move. Absence of skin reflexes and blindness may be seen. Clinically VEE is the most severe followed by EEE and WEE. Mortality may be upto 50% in WEE and 90% in VEE.

Diagnosis: Standard methods of virus detection, isolation and serology are also available for disease confirmation. Virus can be isolated from field specimens by inoculating newborn mice, 6-8 days old embryonated eggs (yolk sack route), cell  cultures (BHK-21, Vero cells, RK-13  etc. Serological tests, viz. plaque reduction, virus neutralization, haemagglutination inhibition test, complement fixation test and IgM capture enzyme linked immunosorbent assay are used for detection of virus- specific antibodies. RT PCR is also used for the diagnosis

Prevention and control: Immunization of horses with inactivated or attenuated vaccines forms the basis of their control. In endemic areas, bivalent or trivalent vaccines with combination of attenuated EEE, WEE and VEE virus is usually given. Vaccination is repeated annually for permanent protection.