EEE and WNV confirmed in New Jersey horses

New Jersey animal health officials have confirmed additional cases of mosquito-borne diseases in horses in that state.

A 10-year old Burlington County mare is the first reported case of West Nile virus (WNV) and an Ocean County gelding is the fourth reported Eastern equine encephalitis (EEE) case in New Jersey for 2018. Neither horse had been vaccinated against WNV or EEE in 2018.

The Burlington County mare is undergoing treatment while the Ocean County horse was euthanized on Sept. 4. The other three EEE cases in 2018, all euthanized, were in Monmouth and Camden counties.

With the higher than average number of mosquitoes this season in New Jersey and a 40% increase in WNV-positive mosquitoes compared to 2017, livestock owners are strongly encouraged to vaccinate against WNV, EEE, and other mosquito-borne diseases.

“We continue to encourage horse owners be vigilant in vaccinating their animals against these diseases spread by mosquitoes,” New Jersey Secretary of Agriculture Douglas H. Fisher said. “Vaccinated animals are much less likely to contract deadly diseases such as EEE and West Nile virus.”

In 2017, officials confirmed two WNV cases and six EEE cases in New Jersey horses.

WNV 101

West Nile virus is transmitted to horses via bites from infected mosquitoes. Not all infected horses show clinical signs, but those that do can exhibit:

  • 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’re daydreaming or “just not with it”;
  • Occasional drowsiness;
  • Propulsive walking (driving or pushing forward, often without control); and
  • Spinal signs, including asymmetrical weakness; and
  • Asymmetrical or symmetrical ataxia (incoordination).

West Nile has no cure, however some horses can recover with supportive care. Equine mortality rates can reach 30-40%.

EEE 101

A viral disease, EEE affects the central nervous system and is transmitted to equids by infected mosquitoes. Clinical signs in horses 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; and
  • Severe central nervous system signs, such as head-pressing, circling, blindness, and seizures.

The disease can progress rapidly, with death occurring two to three days after onset of clinical signs despite intensive care in some cases. Fatality rates can reach 75-80%. Equids that survive might have long-lasting impairments and neurologic problems.

Preventing Disease

Studies have shown that vaccines can be effective in preventing both EEE and WNV. Horses vaccinated in past years need an annual booster shot, but veterinarians might recommend two boosters annually—one in the spring and another in the fall—in areas with prolonged mosquito seasons. In contrast, previously unvaccinated horses require a two-shot vaccination series in a three- to six-week period. Full immunity takes several weeks to achieve.

In addition to vaccinations, owners should work to reduce the mosquito populations and possible breeding areas and horses’ exposure by:

  • Removing stagnant water sources;
  • Dumping, cleaning, and refilling water buckets and troughs regularly;
  • Keeping animals inside during the bugs’ feeding times (typically early in the morning and evening); and
  • Applying mosquito repellents approved for equine use.

Disease Reporting

In New Jersey EEE and WNV, like other viral diseases affecting a horse’s neurologic system, must be reported to the state veterinarian at 609/671-6400 within 48 hours of diagnosis. The New Jersey Animal Health Diagnostic Laboratory is available to assist with EEE and WNV testing and can be reached at 609/406-6999 or jerseyvetlab@ag.nj.gov.