Cattle drug proves effective against equine piroplasmosis

November 9, 2009

A drug used for treating cattle and sometimes dogs for a blood parasite can completely eliminate the parasite Babesia caballi from horses if given at a relatively high dose, scientists have discovered.

Equine piroplasmosis is a tick-borne disease of horses caused by two protozoans - Babesia equi (or Theileria equi) and Babesia caballi.

The drug imidocarb dipropionate, has been used in the United States for many years to treat diseases such as Texas fever, also referred to as cattle fever or babesiosis in cattle.

In response to the needs of US veterinarians, research leader Don Knowles and his colleagues at the animal Disease Research Unit of the Agricultural Research Unit (ARS) in Pullman, Washington, studied the effectiveness of the drug in horses.

They found that a relatively high dose of the drug not only eliminated Babesia caballi, but also left the horses incapable of transmitting the disease.

Though the high dose of the drug was generally well-tolerated by horses, some side effects included stomach upset and diarrhoea. Similar collaborative research is being conducted concerning the effectiveness of imidocarb and other potential drugs on B. (Theileria) equi.

The ARS researchers worked with scientists at Washington State University in Pullman and with the US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS).

In the United States, equine piroplasmosis is considered a foreign disease in horses, though it is common in nearby locales, including the US territory of Puerto Rico.

An outbreak among more than 100 horses is currently under investigation in Texas.

It is important to ensure complete elimination of the parasite behind the disease 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 country.

The findings were published in the journal Antimicrobial Agents and Chemotherapy.

Equine piroplasmosi is distributed worldwide, but appears to be absent from the Pacific region, where it has not been reported since 1976 (Australia).