Drug Eliminates Parasite that Causes Babesiosis in
September 28, 2009
A drug commonly used to treat
cattle and sometimes dogs for a blood parasite can, at a relatively high dose,
completely eliminate the parasite Babesia caballi from horses,
Agricultural Research Service (ARS)
scientists have discovered.
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 response to the needs of U.S. veterinarians, research leader
Knowles and his colleagues at the
Animal Disease Research Unit in Pullman, Wash., studied the effectiveness
of the drug in horses. They found that a relatively high dose of the drug not
only eliminated B. caballi, but also left the horses incapable of
Though the high dose of the drug is generally well-tolerated by horses, some
side effects include stomach upset and diarrhea. Similar collaborative research
is being conducted concerning the effectiveness of imidocarb and other
potential drugs on B. (Theileria) equi.
The ARS researchers collaborated with scientists at
Washington State University in Pullman and
with USDA's Animal and Plant Health
Inspection Service (APHIS).
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 country.
This work was published in the journal Antimicrobial Agents and Chemotherapy.
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.