NASHVILLE, Tenn. (WKRN) — Four horses in Tennessee have tested positive for the bacteria illness Potomac Horse Fever, according to the Tennessee Department of Agriculture.

The cases were confirmed in Robertson, Hawkins and Sullivan counties, in addition to a case in Wilson County where a horse had to be euthanized earlier this month.

“Transmission of this disease can be prevented,” said State Veterinarian Dr. Samantha Beaty. “Potomac Horse Fever is preventable with regular vaccinations and environmental management. In addition to having your horses on a routine medical schedule, make sure they have clean drinking water. One way to do this is change from natural drinking water sources to frequently-cleaned water buckets.”

Potomac Horse Fever is caused by Neorickettsia risticii, bacteria believed to be carried by aquatic snail larvae and other hosts, including flies.

The fever is not contagious between horses and it is not a threat to humans.

Horses that live near bodies of water or low-lying areas that could collect stagnant water are at risk. In addition to clean drinking water, horse owners can reduce risk of exposure by turning off insect-attracting stable lights at night.

Horse owners should look for signs of infection, including anorexia, diarrhea, colic, fever and laminitis, which can appear within two to 18 days after ingestion and can be fatal if left untreated.