ST. PAUL — Minnesota has confirmed its first case of West Nile virus in a horse this year.

The Minnesota Board of Animal Health said Tuesday an unvaccinated horse in Winthrop, in the south-central part of the state, has tested positive for the mosquito-borne disease and is severely ill.

Officials say the year-and-a-half-old Friesian stallion has been unable to stand for a week and is receiving supportive care.

West Nile virus is regularly found in the U.S. Birds serve as the primary host of the disease. Infected mosquitoes can transmit the virus from birds and then carry it to horses and humans.

The virus can cause encephalitis, an inflammation of the brain and spinal cord. Many infected horses recover completely, especially with annual vaccinations.