In 2015, the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) confirmed 38 Texas horses infected with West Nile virus (WNV) and six cases of Eastern Equine Encephalitis (EEE). Currently, flood conditions in parts of Texas will produce favorable mosquito habitat when floodwaters recede. By May 2016, cases of EEE have already been reported in Florida and South Carolina. As with many of the Texas cases in 2015, these positives were reported in non-vaccinated horses.
Terry S. Hensley, MS, DVM, TVMDL assistant director and Texas A&M AgriLife Extension Service veterinarian says that Texas horses should be vaccinated annually because of the state’s history with WNV and EEE. He suggests that owners should work with their veterinarian in deciding on a vaccination program based on their horse(s) disease risk factors.
“While a long distance from Texas, this may be indicative of another year of an increase in mosquito-borne disease cases, especially following the recent weather events,” he said. “These diseases exist in a regular naturally-occurring cycle between wild birds and mosquitoes. When there is an increase in both the mosquito population and the circulating virus, the potential for these diseases to spillover to horses and humans is much higher. However, there is no direct spread from horse-to-horse or horse-to-human.”
While WNV, EEE and Western Equine Encephalitis (WEE) may cause similar neurological signs, other diseases such as Equine Herpesvirus-1 (EHV-1), can also result in a similar neurological presentation. Therefore, Dr. Hensley recommends horse owners work closely with their veterinarian to determine the cause of their horse’s illness.
Clinical presentation for neurologic disease is similar for EHV-1, WNV, EEE and WEE. Diagnostic testing is the only method to differentiate between the various infectious causes of neurologic disease in the horse. If a horse shows clinical signs of neurologic disease, TVMDL recommends veterinarians request an encephalitis panel as well as individual diagnostic tests for each potential disease in order to have a complete diagnostic picture. These tests should look for EHV, EEE, WNV and Western Equine Encephalitis. Rabies should also be considered in a horse that dies or is euthanized due to an undiagnosed neurologic condition.
The Texas Department of State Health Services and the Texas Animal Health Commission have information related to WNV and mosquito control available for free download. For more information on TVMDL’s equine neurologic testing, visit tvmdl.tamu.edu, or contact the agency headquarters at 1.888.646.5623.