Three Nevada Horses Test Positive for West Nile

Three Nevada Horses Test Positive for West Nile

West Nile is transmitted to horses via bites from infected mosquitoes.

Photo: Gbohne/Wikimedia Commons

The Nevada Department of Agriculture (NDA) has confirmed three horses tested positive for West Nile virus (WNV) in the western part of the state in the last two weeks. None of the three horses were vaccinated.

“Vaccination is the best protection horse owners have for their animals,” JJ Goicoechea, DVM, the NDA’s state veterinarian, said. “With the increased numbers of mosquitoes this year, it’s important all horse owners take this precaution to prevent the spread of disease.”

West Nile is transmitted to horses via bites from infected mosquitoes. 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

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.

“Vaccinations, in conjunction with practices that reduce exposure to mosquitos, are very effective in protecting horses from WNV,” Goicoechea said. “It’s not too late to prevent the spread of disease.”

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