Animal health authorities investigating an outbreak of equine piroplasmosis on a South Texas ranch have now located 317 positive horses. These horses include 288 on the index ranch, seven on other premises in Texas, one in Alabama, two in California, five in Florida, one in Georgia, five in Louisiana, one in Minnesota, two in North Carolina, three in New Jersey, one in Tennessee, and one in Wisconsin. All known positive horses are under quarantine, and testing of all epidemiologically linked horses is ongoing.

The information was released in a Nov. 13 report issued to the World Organization for Animal Health (Office International des Epizooties, or OIE) by John Clifford, DVM, deputy administrator of the USDA's Animal and Plant Health Inspection Service. See the report.

Officials in the United States have screened all imported horses for piroplasmosis for nearly 30 years. The disease was officially eradicated from the United States in 1988. It is spread by as many as 15 species of ticks, the use of contaminated needles, and possibly through blood-contaminated semen of infected stallions.

Signs of equine piroplasmosis can include a host of nonspecific clinical signs, such as fever or anemia, and some infected horses might appear well. Blood tests are needed to diagnosis the disease. The only treatment is a potent type of chemotherapy that can have serious side effects in some horses