Delaware Reports First Equine WNV Case of 2017

Delaware Reports First Equine WNV Case of 2017

West Nile virus are transmitted to horses via bites from infected mosquitoes.

Photo: Thinkstock

The Delaware State Veterinarian’s Office reported Aug. 15 that it has confirmed that state’s first case of West Nile virus (WNV) in a horse in 2017.

The affected horse, an 11-year-old Quarter Horse mare residing in Kent County, began showing signs of weakness in all four limbs on Aug. 6. The mare lost the ability to stand and was euthanized on Aug. 9. Samples were submitted to the Delaware Public Health Laboratory on Aug. 10, which confirmed the diagnosis of WNV on August 14. The affected mare was not currently vaccinated against WNV.

This is the first confirmed case of WNV in a horse in Delaware since 2015. However, the Department of Natural Resources and Environmental Control’s (DNREC) Mosquito Control Section, in conjunction with the Delaware Division of Public Health Laboratory and the Department of Agriculture, announced two detections of WNV and one detection of another potentially deadly disease, Eastern equine encephalitis (EEE), in the DNREC’s sentinel chickens, and detection of WNV in a wild crow, in July and August. So far in Delaware this year, no cases of WNV or EEE have been found in humans.

West Nile virus and EEE are diseases transmitted to horses via bites from infected mosquitoes. Humans can also be infected with WNV and EEE, but transmission requires a mosquito bite and the virus cannot be directly transmitted between horses, or between horses and people.

Clinical signs of 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. Equine mortality rate can be as high as 30-40%.

Health Alert: West Nile Virus

The Delaware state veterinarian urges horse owners to contact their veterinarians as soon as possible, as the state is in the midst of peak mosquito season, to have horses and other equids vaccinated against WNV and EEE. 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 (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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