June 01, 2003


 USDA requires new test for tickborne horse disease

Posted May 15, 2003

In May, the Department of Agriculture's Animal and Plant Health Inspection Service started requiring horses imported into the United States from other countries to undergo a new test.

According to the Office International des Epizooties, equine piroplasmosis is endemic in South and Central America, the Caribbean, Africa, the Middle East, and Eastern and Southern Europe. The United States is currently deemed free of clinical disease, but remains at risk of introduction from international animal trading and equestrian sports, where infected and noninfected animals mingle.

While the disease doesn't usually cause severe health problems in animals that are routinely exposed to it, some infected American horses can become very ill or die. Signs can include fever, anemia, jaundiced mucous membranes, swollen abdomens, constipation, colic, and labored breathing.

Two parasites, Theileria equi and Babesia caballi, cause piroplasmosis, but, at present, only horses infected with B caballi may be successfully treated. Babesia caballi is sometimes impossible to clear from a horse, and the treatment, which is fairly toxic, can be damaging to the horse, Dr. Isaac said.

The United States is considered free of the disease because there is no evidence of tick transmission of the disease, and there have been no clinical cases of the disease in the country. The USDA, however, can't rely on this.

"In some areas, like southern Texas and southern Florida, local populations of native ticks have the potential, experimentally in the laboratory, to transmit the disease agent," Dr. Isaac said. "But there is no evidence that these ticks are infected and transmit the disease."  

"The new test is more sensitive and more specific," said Dr. Freeda Isaac, a staff veterinarian at the USDA-APHIS who spoke about the CELISA at the recent Animal Transportation Association conference in Washington, D.C. She went on to explain that the CELISA should reduce the risk of not detecting false-positive horses and provide greater confidence in detecting the true disease status of horses being imported into the country. Before the CELISA test, veterinarians performed a complement fixation test to determine a horse's piroplasmosis status. 

The USDA is requiring the new test because it has a greater likelihood of detecting the disease agent than the old test.