Equine piroplasmosis (EP) is an infectious disease of international importance. While some parts of the world deal with it
as a fairly routine equine health problem, other areas are piroplasmosis-free and want to keep it that way.
A significant issue arises with horses in international competition when a positive athlete is barred entry into a negative
country hosting a major event. Piroplasmosis was at the center of debate prior to the 1996 Olympic Games in Atlanta.
Because the U.S. Southeast region has the appropriate climate and the specific type of tick population to support the establishment
and transmission of piroplasmosis, the Georgia Department of Agriculture initially issued a "no piroplasmosis" policy for
potential Olympic horses.
John Quigley, the state veterinarian at that time, spoke before the FEI Samsung International Equine Sports Medicine Conference
in March 1994, stating: "When a nation, country or state is faced with a disease in its livestock population, a decision must
be made to eradicate, control or ignore it and live with it. Why should other nations and countries be expected to take risks
with the possible introduction and spread of equine piroplasmosis within its equine population?"
Georgia's official position was that there would be no waiver of EP for the 1996 Olympics.
Photo 1: Horses on the three-day event course or competing in the 50- or 100-mile endurance championships are exposed to
local vegetation and the species of ticks present in the area surrounding the event. (Photo: courtesy of Dr. Kenneth Marcella)
Two years later, after much debate, discussion, research and international pressure, this hard-line stance was softened, and
horses from piroplasmosis-endemic countries and even positive horses were allowed to enter the United States and to compete
in limited events in Atlanta.
Restrictions were placed on the positive horses, and many types of prevention and surveillance measures were undertaken at
the games. No problems developed during or after the Olympics, the positive horses left the United States and conversation
about piroplasmosis pretty much stopped.
But now, as the 2010 World Equestrian Games in Lexington, Ky., approach, issues about positive EP horses competing, tick removal
and control and the overall threat to the country's horse population have resurfaced. This time around more information is
available about the disease and research, and it is hoped that education will lead to better ways of dealing with piroplasmosis-positive
horses and safer, more effective ways to stop the spread of EP in this country.
Equine piroplasmosis also has been called babesiosis and was commonly referred to as horse tick fever, which provides a clue
to its means of transmission and presenting clinical signs.
EP is a disease of equidae (horses, donkeys, mules and zebras) and is caused by one of two protozoan blood parasites, Babesia equi and Babesia caballi.
The active or acute phase of EP, which occurs within seven to 22 days of exposure, is marked by fever, anemia, jaundice, labored
breathing, rough hair coat, swelling of the abdomen, chest or legs and colic in some cases.
Mild cases may exhibit lack of appetite and general weakness; severe cases result in death. Horses that survive this acute
phase typically become carriers. They recover from the disease and show no symptoms but still harbor the infective organism
and can pass the disease to other horses.
Photo 2: Horses affected with piroplasmosis can exhibit anemia, weakness, lack of appetite, respiratory difficulty, constipation
and intestinal irritation. Supportive therapy, including fluid replacement, may be necessary and piroplasmosis can mimic equine
infectious anemia, colic (as in this photograph) and other diseases. (Photo: courtesy of Dr. Kenneth Marcella)
EP is transmitted from horse to horse primarily by a tick vector. Several species of tick have been identified as capable
of transmitting the Babesia organisms. The primary one is Dermacentor nitens, the tropical horse tick. But Dermacentor albipictus, the winter tick; Dermacentor variabilis, the American dog tick; and Boophilus microplus, the southern or tropical cattle tick, have been shown to be capable of transmitting EP in experimental situations. Contaminated
hypo-dermic needles and other management practices that allow the transfer of sufficient amounts of blood also can pass along
Diagnosis of EP requires a negative test for equine infectious anemia because these two conditions present very similarly.
Direct blood smears can confirm the presence of this parasite within the red blood cell but a competitive enzyme-linked, immunosorbent
assay (cELISA) recently has been developed that should improve accurate diagnosis of EP.