MADISON, Wis. — A horse in Trempealeau County has tested positive for the mosquito-borne West Nile virus, the state Agriculture Department reported. The agency didn’t release the exact site in the 742-square mile Mississippi River county. The case is the first in Wisconsin this year. The disease causes brain inflammation. It is fatal in 30% to 40% of infected horses. Horses experience fever, losr incoordination and appetite, develop tremors, and cannot stand up. The American Association of Equine Practitioners recommends vaccinating all horses.