California animal health officials have confirmed an additional case of West Nile virus (WNV) in a horse in that state.

“On Aug. 18, 2017, an unvaccinated yearling Warmblood filly in San Joaquin County displaying severe neurologic signs was confirmed positive for WNV,” said a statement from the California Department of Food and Agriculture (CDFA). “Due to the severity of clinical signs the filly was euthanized.

“For 2017, a total of seven horses have been confirmed positive for WNV,” the CDFA continued. “The positive horses were located in Glenn, Contra Costa, Fresno, Kern (2), Riverside, and San Joaquin counties. Five horses were unvaccinated and two horses had unknown vaccination status. Five horses died or were euthanized and two horses are recovering.”

West Nile is 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. Equine mortality rate can be as high as 30-40%