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First Posted Dec 29, 2009
Feb 21, 2013

Equine Piroplasmosis/APHIS Factsheet/Veterinary Services July 2008

Update: Optimizing Piroplasmosis Treatment Protocols (AAEP 2012)
"...The tick-borne protozoal disease equine piroplasmosis (EP) impacts horses worldwide, causing hemolytic anemia (the body's immune system attacks and kills its own red blood cells) and even death. Veterinarians' drug of choice for eliminating the causative parasites, Theileria equi and Babesia caballi, is imidocarb dipropionate, which is effective but commonly causes untoward side effects such as severe diarrhea and colic and, in rare cases, liver and kidney toxicity. Researchers in Scotland recently examined ways to minimize gastrointestinal complications when treating EP with this drug. ...when targeting equine piroplasmosis using imidocarb, premedicating with glycopyrrolate prevents gastrointestinal side effects without delaying small intestinal transit. She emphasizes, 'This ultimately improves the welfare of horses.'"

Update - September 30, 2010: This site is an update provided by the USDA/Animal Health/Animal Diseases (A Literature Review of Equine Piroplasmosis)

USDA's Animal and Plant Health Inspection Service

"Equine piroplasmosis (EP) also referred to as babesiosis, is a tick-borne disease that affects horses, donkeys, mules, and zebras. The disease is transmitted via tick bites or through mechanical transmission by improperly disinfected needles or surgical instruments. EP is not endemic to the United States; native tick species do not currently carry the parasites that cause the disease.

Likewise, EP is not endemic to Australia, Canada, England, Iceland, Ireland, and Japan. The disease is, however, found in Africa, the Caribbean (including Puerto Rico), Central and South America, the Middle East, and Eastern and Southern Europe. The increasingly international nature of the horse industry presents potential risks for EP's introduction from foreign countries. Many areas of the United States have climates suitable for foreign tick vectors or other ticks that could act as vectors. Additionally, because EP is not endemic, U.S. horses are highly susceptible to acute forms of the disease. Protecting Equine Health The U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) protects the U.S. equine industry against the entry and spread of EP. APHIS' Veterinary Services (VS) program regulates equine importation and maintains tick control and surveillance programs.

Recently, the United States won the bid to hold the 2010 World Equestrian Games in Kentucky, making it the first time that the games will be held outside of Europe. For the event, VS officials will use specific safeguarding measures to safely allow horses with EP and horses from EP-endemic areas to enter the United States. VS officials will closely monitor EP-positive horses to prevent disease transmission and maintain the health of U.S. equine.


EP is a tick-borne disease caused by the parasites Babesia caballi and B. equi. Ticks ingest blood from infected equine and then bite uninfected equine, spreading the disease through blood contact. Ticks carrying the parasites can be moved via hay, bedding, feed, and vegetation. The only known natural vector of EP in the United States is the tropical horse tick, Dermacentor nitens, found in the southern United States. B. caballi and B. equi have been experimentally transmitted by three other U.S. tick species: D. albipictus, the winter tick; D. variabilis, the American dog tick; and Boophilus microplus, the southern or tropical cattle tick. Because the disease spreads through contact with blood, EP can also be transmitted through contaminated needles and other skin-penetrating instruments. Intrauterine infection from mother to foal is also common.


An EP-infected horse can take 7 to 22 days to show signs of the disease. Cases of EP may be mild or acute. Mild forms of the disease cause equines to appear weak and show lack of appetite. More acute cases can occur where EP is not common and horses have not built up a resistance to the disease. Signs of the acute phase include fever, anemia, jaundiced mucous membranes, a swollen abdomen, and labored breathing. Other signs of EP include central nervous system disturbances, roughened-hair coats, constipation, colic, and hemoglobinuria-a condition which gives urine a red color. In some cases, death may occur. Some infected horses, however, may show few or no symptoms in the acute phase and may not experience any decrease in performance. Horses that survive the acute phase of infection may continue to carry the parasites for long periods of time. These horses are potential sources of infection to other horses through tick-borne transmission or mechanical transfer by biting ticks, needles, or surgical instruments.


Because the clinical signs for EP are non-specific and similar to many other diseases and conditions, it is difficult to diagnose; the disease, however, can be diagnosed with laboratory tests. If EP is suspected, State or Federal animal health officials should be notified before veterinarians collect any samples If an outbreak of EP occurs, APHIS must notify the World Organization for Animal Health (OIE) and indicate the steps it is taking to eradicate the disease. The OIE is the international organization that establishes standards for the safe international trade of animals and their products.


Currently, there is no vaccine for EP. In endemic regions, symptoms of EP are treated with drugs. While disinfectants and proper sanitation are often crucial to preventing the spread of animal disease, United States Department of Agriculture - Animal and Plant Health Inspection Service - Safeguarding American Agriculture The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities..."

For More Information:

Understanding Piroplasmosis
Piroplasmosis Equine (Horse)
Equine piroplasmosis/Etiologic agents: Theileria and Babesia spp. parasites/Tests

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