Drug Eliminates Parasite that Causes Piroplasmosis in Horses

B. caballi, a blood parasite transmitted by ticks, is one of the culprits behind the disease babesiosis in horses. Equine babesiosis is also caused by another blood parasite called Babesia (Theileria) equi. The drug imidocarb dipropionate has been used in the United States for many years to treat diseases like Texas fever, also referred to as cattle fever or babesiosis in cattle.

In equine, babesiosis is an acute, subacute, or chronic infectious hemolytic disease caused by the intraerythrocytic protozoa Babesia equi and Babesia caballi. The disease is also known as equine piroplasmosis and "biliary fever." Endemic in most tropical and subtropical regions of the world, this infection has been documented in horses, mules, donkeys, and zebras. The occurrence of equine babesiosis has been tied closely with the geographic distribution and seasonal activity of its biological vectors: species of ticks in the genus Dermacentor, Rhipicephalus, and Hyalomma.

Horses become infected with the Babesia organism when they are parasitized by feeding ticks that harbor the sporozoites in their salivary secretions. Ticks acquire the organism by taking a blood meal from infected horses. (Reference: http://www.vet.uga.edu/VPP/clerk/edwards/index.php). Historically, babesiosis has had the greatest impact in southern Africa, where it was first described around the turn of the century as "anthrax fever," "biliary fever," a "billous form" of African Horse Sickness, or "equine malaria." Recently, equine babesiosis has spread from its endemic subtropical zones to more temperate regions as global transport of equids has increased greatly.

In the United States, babesiosis is considered a foreign disease in horses, though it is common in nearby locales including the U.S. territory of Puerto Rico. It is important to assure complete parasite elimination because infected horses can appear healthy, but can still transmit the disease.

Horses presented for import into the United States are tested at the border. Those that test "positive" are either destroyed or returned to their place of origin. However, infected horses occasionally escape detection and enter the United States. Since such horses are often retested for subsequent international movement, they are then discovered to be infected and placed under quarantine at great expense to the state and the owner. Therefore, methods to eliminate the parasite from such horses and eliminate transmission risk were sought.

If approved for use in the United States, imidocarb dipropionate would offer a humane way to clear horses of B. caballi and allow them to enter or remain in the United States. (Reference: http://www.ars.usda.gov/is/pr/2009/090928.htm)