Horses face high mortality rates from core diseases (those that can infect any horse of any age), including Eastern equine encephalomyelitis (EEE), Western equine encephalomyelitis (WEE) and West Nile virus (WNV). And, because all three diseases are transmitted via bites from infected mosquitoes, horses are at the greatest risk when these insects are most prevalent—late spring through fall in the United States. Risk management is critical for horse owners during this time.
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.
Clinical signs for WNV, also transmitted by bites from infected mosquitoes, include flulike signs, where the horse seems mildly anorexic and depressed; fine and coarse muscle and skin fasciculation; hyperesthesia; 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%.
“To help limit a horse’s risk of contracting deadly core equine diseases, annual vaccinations are immensely important,” said Jaci Boggs, DVM, senior technical services veterinarian at Zoetis.
Annual vaccination can help protect horses against mosquito-borne diseases. Studies have shown that vaccinated horses can be 30 times less likely to contract WNV than their unvaccinated counterparts.
“In conjunction with annual vaccination, proper management of the environment to limit mosquito breeding opportunities is critical,” Boggs said.
Try implementing these five barn-friendly mosquito management tips:
- Remove objects that can collect water, such as unused troughs, wheelbarrows, and tarps, to eliminate mosquito-breeding habitats;
- Empty and clean any water-holding containers (including water buckets) at least weekly;
- Fill in any low-lying areas or prevent them from collecting standing water after rainfall;
- Hang fans throughout the barn where horses are stabled, as mosquitoes avoid moving air; and
- Apply insect repellent or bring horses inside from dusk to dawn, which are peak mosquito feeding hours.
“It’s important for horse owners to remember that West Nile virus cases continue to occur across the United States,” Boggs said. “An unvaccinated horse is very much at risk for core equine diseases, such as West Nile, EEE, and WEE.”
All horses need annual core disease vaccination as the foundation of their wellness program. Contact your veterinarian today to discuss vaccinating amid an emerging mosquito population.