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). The positive cases were found from the Panhandle to Dallas, to South Texas and the Houston area. The most prolific area with positive cases was the southeastern region of the state.

The common factor in each case was confirmation from the owner or veterinarian that the horse had not been vaccinated for these common neurologic diseases. 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.

“Horse owners may want to save a few dollars by not vaccinating their horse for some of the diseases they see as uncommon to their home area,” he said. “But the wide geographic range of cases in 2015 dispels the belief that only horses in areas of the Texas with higher rainfall are susceptible to these mosquito-borne diseases.”

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.

“Vaccinating for all three mosquito-borne diseases, West Nile, EEE and WEE is important for all horses, as well as mules and donkeys,” Dr. Hensley said. “The AAEP [American Association of Equine Practitioners] lists these three diseases and rabies and tetanus as diseases for which the majority of horses be vaccinated.

“If the horse travels to shows, competitions, breeding farms, boarding stables, etc they are at increased risk of exposure to infectious diseases and horse owners need to work closely with their veterinarian to design an appropriate vaccination program. A proper vaccination program is one of the most cost effective preventative health measures that an owner can do.”

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.

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.

Texas A&M Veterinary Medical Diagnostic Laboratory
1 Sippel Road | PO Drawer 3040
College Station, Texas 77843
1.888.646.5623 | tvmdl.tamu.edu

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