Additional EEE, WNV Cases Confirmed in New Jersey Horses

Additional EEE, WNV Cases Confirmed in New Jersey Horses

Both EEE and WNV are transmitted to horses via bites from infected mosquitoes.

Photo: iStock

The New Jersey Department of Agriculture Division of Animal Health issued a memo Oct. 6 confirming that additional horses in that state have tested positive for Eastern equine encephalitis (EEE) and West Nile virus (WNV).

The memo indicated that a 15-year-old unvaccinated mare from Cumberland County was the third confirmed positive EEE case in New Jersey horses in 2017; the mare was euthanized. Additionally, a 10-year-old unvaccinated stallion in Salem County is the second confirmed equine WNV in New Jersey this year. The stallion is currently being treated.

Health Alert: EEE, WEE, VEE

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.

Health Alert: West Nile Virus

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; 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. There are no specific treatments for WNV, however supportive care can help horses recover in some cases. Equine mortality rate can be as high as 30-40%.

Vaccines have proven to be a very effective prevention tool for both EEE and WNV. Horses that have been vaccinated in past years will need an annual booster shot; in areas with a prolonged mosquito season, veterinarians might recommend two boosters annually—one in the spring and another 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, which are typically early in the morning and evening, and applying mosquito repellents approved for equine use.

In 2016, New Jersey confirmed four cases of equine EEE between mid-August and mid-September. No cases of equine WNV occurred in New Jersey in 2016.

Like other viral diseases affecting horses’ neurologic systems, cases of EEE and WNV in New Jersey must be reported to the state veterinarian within 48 hours, and a neurologic disease worksheet must be completed for each case reported.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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