Breeding and Piroplasmosis

As the equine piroplasmosis investigation unfolds, let’s look at how the disease affects mares and foals.

Equine piroplasmosis, a disease most commonly transmitted by ticks, has recently been identified in three New Mexico horses during a racetrack screening program. The infection is caused by protozoa - Babesia caballi or Theileria equi (formerly Babesia equi) - and affects horses, donkeys, mules and zebras. According to a report

posted by the American Veterinary Medical Association, Theileria equi results in more severe infection and disease, resulting in the destruction of up to 20 percent of the horse's red blood cells. Some affected horses die within 24 to 48 hours of onset of clinical signs. Breeders should be aware of the disease’s impact on mares and foals. Intrauterine infection of foals can occur. Foals infected in utero may be aborted or may be born anemic and weak. Foals born to infected dams, but that are not infected in utero, will usually become carriers of the disease.

Learn the steps for preparing your mare for breeding and get the facts on receiving shipped semen with AQHA's Mare Care: Breeding Tips report.

Affected horses may be feverish and become anemic with an increased breathing and heart rate. This is a result of the decrease in number of circulating red blood cells and the associated reduction in oxygen-carrying capacity of the blood. Red-tinged urine and jaundice develop due to the release of free hemoglobin into the blood from ruptured red blood cells. If sufficient amounts of free hemoglobin are present in the bloodstream or if a sufficient number of erythrocyte (red blood cell) aggregates accumulate, kidney damage and subsequent failure can result. Because it is the primary organ involved in removing damaged red blood cells, the spleen is usually enlarged. AVMA also reported that as many as 50 percent of affected horses will die. This number is highest for equine infected with T. equi.

Spread of Disease

Dr. Peter Timony of the University of Kentucky’s Gluck Equine Research Center told The Horse that the parasites are blood-borne and consumed by ticks that ingest the blood from infected equine. The ticks then transmit the disease by biting uninfected equine. This is the primary source of spreading the disease. Ticks carrying the parasites can be moved via hay, bedding, feed and vegetation. Timony added that the use of contaminated syringes and needles on unexposed animals may also be a method of transmitting the disease. The disease could additionally be transmitted through blood-contaminated semen of infected stallions.

AQHA's Mare Care: Breeding Tips report gives you the tips you need to know for breeding season.

Prevention and Control

According to the Institute for International Cooperation in Animal Biologics, a World Organization for Animal Health Collaborating Center, carrier animals or infected ticks can introduce equine piroplasmosis into new regions. Equids are usually tested for this disease during importation. IFA and ELISA tests are highly sensitive, but complement fixation may not detect all carriers. Disinfectants and sanitation are not generally effective against the spread of tick-borne infections. However, eliminating contact with ticks and preventing the transfer of blood from one animal to another are vital. In endemic areas, the use of acaricides (pesticides that kill ticks), together with frequent examination of horses and immediate removal of ticks (since parasite transmission does not occur immediately), may help prevent infection. If an infected animal is discovered in a piroplasmosis-free region, the animal must be quarantined and kept from all contact with ticks.