Equine diseases that are usually rare in the United States sometimes crop up without warning.

Recently, almost two dozen horses in Tennessee were diagnosed with equine piroplasmosis. The infection is caused by microscopic parasites that are transmitted either by ticks or by contaminated surgical or tattooing equipment. Horses cannot be infected by casual contact, but affected horses are quarantined nonetheless.

Some infected horses don’t show clinical signs. Others may develop anemia, fever and jaundice. More obvious signs include anorexia and depression, a bloated abdomen and labored breathing.

Some states and horse events require an equine piroplasmosis test for entrance, so check with authorities before traveling with your horse. And keep in mind that it can take up to one month for an infected horse to test positive.