Additional EEE, WNV Cases Confirmed in New York Horses

Additional EEE, WNV Cases Confirmed in New York Horses

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

Photo: Thinkstock

The Equine Disease Communication Center (EDCC) reported Oct. 10 that additional New York horses have tested positive for Eastern equine encephalitis (EEE) and West Nile virus (WNV).

The New York State Department of Agriculture and Markets (NYSDAM) reported that an Oswego County horse tested positive for EEE and has been euthanized, the EDCC said.

Meanwhile, NYSDAM has confirmed four additional WNV cases. One horse from St. Lawrence County is still alive but was not vaccinated for the disease, the EDCC said, while the three other horses—which resided in Cayuga, Erie, and St. Lawrence counties—have been euthanized. The EDCC said two of those three were not vaccinated, and the other horse had been vaccinated but not enough time had elapsed for the vaccine to be protective.

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.

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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