Maryland Horse Owners: Keep Vaccinations Up-To-Date

Maryland Horse Owners: Keep Vaccinations Up-To-Date

Horses that have been vaccinated in past years need an annual booster shot.

Photo: Erica Larson, News Editor

As a result of heavy rains and increased mosquito populations, the Maryland Department of Agriculture is strongly encouraging owners to make sure their horses and other equids are vaccinated against West Nile virus (WNV) and Eastern equine encephalomyelitis (EEE), two potentially fatal diseases that are spread by mosquitoes.

“Preventing a disease is always less expensive and traumatic than treating it, so we urge horse owners to be proactive and vaccinate their horses now that mosquito season is in full swing,” said Maryland State Veterinarian Michael Radebaugh, DVM. “Your veterinarian is the best source of information and advice for your horse and its health. We also remind veterinarians across the state that they must report any cases of equine arboviruses to the department.”

A viral disease, EEE affects the central nervous system and is transmitted to horses by infected mosquitoes. 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; fatality rates reach 75-80% among horses. Horses that survive might have long-lasting impairments and neurologic problems.

West Nile is also 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 (twitching); 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%.

Horses that have not already been vaccinated this year for WNV or EEE 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.

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), using fans to disrupt mosquitoes’ flight patterns, and applying mosquito repellents approved for equine use.

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