Texas Owners: Vaccinate Against Mosquito-Borne Illnesses

Texas Owners: Vaccinate Against Mosquito-Borne Illnesses

Photo: Anne M. Eberhardt/The Horse

The Texas Animal Health Commission (TAHC) is encouraging owners to take precautions and vaccinate their equids to protect against the West Nile virus (WNV) and Eastern equine encephalitis (EEE).

As of Sept. 1, the Texas Department of State Health Services has reported five cases of WNV and one case of EEE in 2017.

In addition to vaccinations, horse owners also need to reduce the mosquito populations and their possible breeding areas. Recommendations include removing stagnant water sources, keeping animals inside during the bugs' feeding times (typically early in the morning and evening), and using mosquito repellents.

West Nile is transmitted to horses via bites from infected mosquitoes. Clinical signs for WNV include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculation; hyperesthesia (hypersensitivity to touch and sound); changes in mentation (mentality), when horses look like they are daydreaming or "just not with it"; occasional somnolence (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%.

A viral disease, EEE affects the central nervous system. Clinical signs of EEE 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. Horses that survive might have long-lasting impairments and neurologic problems.

As part of routine equine health care, the TAHC strongly recommends that equine owners consult with their local veterinarians to discuss an appropriate vaccination program to protect their horses against mosquito-borne diseases. Horses that have not already been vaccinated this year for EEE or other mosquito-borne diseases are at greater risk, but it is not too late to vaccinate. Horses that have been vaccinated in past years will need an annual booster shot; in areas with a long mosquito season, veterinarians might recommend two boosters per year—one in the spring and one in the fall. However, if an owner did not vaccinate their animal in previous years, the horse will need the two-shot vaccination series within a three- to six-week period.

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