NASHVILLE (AP) — Tennessee's state veterinarian's office is investigating an outbreak of a blood parasite in a group of racing quarter horses.

The office says 22 horses have tested positive for equine piroplasmosis in five locations within Bedford, Rutherford and Williamson counties.

It can take up to 30 days for an infected horse to test positive after exposure. Horses that do test positive are quarantined and may be euthanized. Those that survive will continue to carry the parasite for an extended period.

Horses will not transmit the disease to other horses through casual contact. It is commonly spread through shared needles or improperly cleaned dental, surgical or blood product equipment.

Early signs of the disease can include weakness, lack of appetite, swollen limbs and labored breathing.