An unvaccinated yearling Standardbred-cross gelding from Clark County is the first reported Wisconsin horse to have become infected with West Nile virus (WNV) this year. The gelding was euthanized.

"It’s been a very wet summer so far this year, which contributes to a growing mosquito problem,” said Julie McGwin, DVM, equine program veterinarian for the Wisconsin Department of Agriculture, Trade, and Consumer Protection.

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%.

The virus is not contagious between horses, but can be carried by mosquitos from a bird to horses and humans. While humans can contract WNV, the virus does not pass directly between people and horses. Mosquitoes biting warm-blooded animals is the only route of transmission