A horse from Mercer County is the latest to reportedly have acquired the West Nile virus, according to the state health department.

State officials Monday reported numerous positive statewide West Nile virus tests, including the horse from Mercer County which tested positive, bringing a total of 12 equine cases in six Pennsylvania counties.

The location of the horse in Mercer County was not released.

Mosquitoes get the West Nile virus from infected birds and pass it on to other birds, animals and people. Horses and birds are the most susceptible to the virus, according to the department. Horses may become ill after the virus infects the central nervous system, causing symptoms of encephalitis, an infection that can result in inflammation of the brain.

The majority of horses that were reported to have West Nile within the past three years either were not vaccinated or weren't vaccinated according to recommendations.

Clinical signs most commonly reported in Pennsylvania horses sick from West Nile virus in Pennsylvania included: weakness, mainly in the hind end, stumbling, a lack of coordination, difficulty rising without assistance, hypersensitivity around the head, muscle and muzzle twitching, mild fever and lethargy. It helps for horse owners to keep accurate vaccination records..

People with questions about the West Nile virus vaccine for horses can contact the Fort Dodge Animal Health Customer Service number 1-800-685-5656.