Texas Horse Owners: Take Steps to Protect Against EEE, WNV

Mosquitoes transmit both EEE and WNV.

Photo: Thinkstock

Texas animal health officials are cautioning owners that horses in that state have tested positive for Eastern equine encephalitis (EEE) and West Nile virus (WNV).

On July 30, the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) reported that a horse in Jefferson County, on the southeastern Gulf Coast, tested positive for WNV.

“This is the third confirmed (equine) case of WNV in Texas in 2015, and as with other positive cases, the horse was not vaccinated for WNV,” a TVMDL statement said. “Clinical signs alerted the horse’s owners to a potential problem: mild depression and muscle fasiculations.”

Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculations (twitching); hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional drowsiness; propulsive walking (driving or pushing forward, often without control); and "spinal" signs, including asymmetrical weakness. Some horses show asymmetrical or symmetrical ataxia. Equine mortality rate can be as high as 30-40%.

Additionally, the Texas Animal Health Commission (TAHC) said July 30 that the TVMDL has confirmed five EEE cases in Texas horses this year. The infected horses are located in Newton, Orange, Liberty, Jasper, and Jefferson counties.

Officials with the TAHC are reminding owners to consult with their private veterinary practitioner regarding vaccinating their horses against mosquito-borne illnesses such as EEE, Western equine encephalitis (WEE), Venezuelan equine encephalitis (VEE), and WNV.

Another viral disease, EEE affects the central nervous system. Clinical signs include moderate to high fever, depression, lack of appetite, cranial nerve deficits (facial paralysis, tongue weakness, difficulty swallowing), behavioral changes (aggression, self-mutilation, or drowsiness), gait abnormalities, or severe central nervous system signs, such as head-pressing, circling, blindness, and seizures. The course of EEE can be swift, with death occurring two to three days after onset of clinical signs despite intensive care; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems.

Similar to EEE, WEE is characterized by central nervous system dysfunction, and about 20 to 50% of horses infected with WEE die.

Venezuelan equine encephalitis (VEE) is a viral disease that affects horses and causes illness in humans. It has not been seen in the United States for many years; however, a recent VEE outbreak occurred in Mexico). Clinical signs in horses vary widely, but all result from the degeneration of the brain; early signs can include fever, depression, and appetite loss. The mortality rate for VEE is 40 to 80%.

"Vaccines are available for neurologic diseases such as EEE and WEE,” said Andy Schwartz, DVM, TAHC assistant executive director. “As part of routine equine health care, we strongly recommend that equine owners consult with their local veterinarian to discuss an appropriate vaccination program to protect their horses against mosquito-borne diseases such as these."

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