APHIS Factsheet

Veterinary Services July 2008

Equine Piroplasmosis

Equine piroplasmosis (EP) 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. 

 

Transmission

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.

Signs

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.

Diagnosis

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.

Treatment

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 on the basis of race, color, 

national origin, age, disability, and where applicable, sex, marital 

status, familial status, parental status, religion, sexual orientation, 

genetic information, political beliefs, reprisal, or because all or part 

of an individual’s income is derived from any public assistance 

program. (Not all prohibited bases apply to all programs.) Persons 

with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) 

should contact USDA’s TARGET Center at (202) 720–2600 (voice 

and TDD). To file a complaint of discrimination, write to USDA, 

Director, Office of Civil Rights, 1400 Independence Avenue, S.W. , 

Washington , D.C. 20250–9410 , or call (800) 795–3272 (voice) or 

(202) 720–6382 (TDD). USDA is an equal opportunity provider and 

employer. 

these practices are not necessarily effective against 

the spread of EP and other tick-borne infections. 

Preventing the transfer of blood between animals 

through biting ticks or surgical instruments is crucial 

to preventing the transmission of EP. 

History

In 1960, VS and the State of Florida began a disease 

investigation after backyard horses in south Florida 

became ill with progressive anemia, jaundice, and 

fever. The investigation determined that the illness 

was EP and that it was carried by tropical horse ticks. 

A State-Federal EP control program was initiated in 

1962 in south Florida to eradicate the disease. The 

program used quarantine and drug treatment for 

infected equines, spray treatment for infected and 

exposed animals, and movement controls to prevent 

disease spread of EP. As a result of the eradication 

campaign, the United States was declared EP-free in 

1988.

Additional Information

For more information about EP, contact:

USDA, APHIS, Veterinary Services, National Animal 

Health Programs

4700 River Road, Unit 43

Riverdale, MD 20737

Telephone (301) 734–6954

Fax (301) 734–7964

Current information on animal diseases is also 

available on the Internet at www.aphis.usda.gov/.