By the AAEP
1. What is Equine Piroplasmosis?
Equine Piroplasmosis (EP) is a tick-borne disease that affects horses, donkeys, mules and zebras. The disease is transmitted via ticks or through mechanical transmission by improperly sanitized surgical, dental or tattoo instruments, through the reuse of needles and syringes, or through the administration of contaminated blood products. EP is considered to be a foreign animal disease in the U.S., but it occurs in many other areas of the world.
2. How is Equine Piroplasmosis spread?
EP agents are spread by certain species of ticks, which transfer the parasites (Babesia caballi and/or Theileria (Babesia) equi) from one horse to another. Ticks ingest blood from the infected equine and transfer the parasite to an uninfected equine by feeding on the host, spreading the disease through blood contact. Because the disease is spread through blood, EP can also be transmitted through blood transfusion when the source of blood is an infected horse, previously used needles or syringes and other skin penetrating instruments that are contaminated with blood and have not been adequately sanitized between horses (i.e. dental, tattoo and surgical equipment). T. equi can be transmitted from an infected dam to her foal, although this route of transmission is uncommon.
3. What are some of the signs of EP?
An infected horse can take 5 to 30 days to show signs of the disease. Mild forms of EP can appear as weakness and lack of appetite. More severe signs include fever, anemia, weight loss, jaundiced mucous membranes, a swollen abdomen (edema fluid accumulation), swelling of the limbs and labored breathing. Other signs of EP can include central nervous system disturbances, roughened hair coats, constipation, colic and hemoglobinuria – a condition which gives urine a reddish or dark brown color to the urine. Chronic infection often results in nonspecific clinical signs such as mild inappetence, poor performance and weight loss. The spleen may be enlarged on rectal examination. Some cases may progress to death. Some infected horses may, however, show few or no signs of disease after infection and may not experience any noticeable decreased performance.
Horses that survive the acute phase of infection continue to carry the parasites for long periods of time. These horses, often called chronic carriers, are potential sources of infection for other horses through tick-borne transmission or mechanical transfer by reuse of needles/syringes or surgical, dental or tattoo instruments that have not been adequately sanitized between horses.
4. How is EP diagnosed?
Clinical signs for EP are non-specific and similar to many other diseases and conditions, therefore laboratory tests are needed to make a diagnosis of EP. If EP is suspected, State or Federal animal health officials must be notified so they can further investigate the case.
In horses with clinical signs of EP, the parasite may be detected on microscopic examination of a blood smear, but detection of the parasite is not always possible by this method of testing. The most commonly used tests are serologic tests that detect antibodies to the organism in blood. The USDA recognizes the cELISA (competitive enzyme-linked immunosorbent assay) as the standard test for screening for chronic EP infection and the complement fixation test (CFT) in cases of more recent infection; there is a separate tests for B. caballi and T. equi. In an outbreak situation, different types of tests are often needed to determine the infection status of a horse.
Several equine events (racetracks and some shows) now require horses be tested for the infection before allowing them to compete. The test used for this purpose is the cELISA test conducted by one of the veterinary diagnostic laboratories in the U.S. approved to conduct the test.
5. How is EP treated?
Treatment of EP cases in the U.S. is only permissible if the horse is enrolled in the USDA supervised EP treatment program. The goal of treatment of infected horses in the U.S. is removal of all transmission risks which requires permanent eradication of the organism from the horse. To confirm achievement of this goal, state and federal animal health officials must oversee the administration of treatment and post-treatment testing of the horse.
6. What are some prevention methods for EP?
Currently all known infected horses are under official quarantine. However, since carrier horses can appear normal and may not have undergone testing, some basic precautions can reduce the risk of transmission of EP agents.
Preventing the transfer of blood between animals through control of ticks and avoiding use of equipment that could be contaminated with blood from previous use is crucial to preventing the transmission of EP.
In recent history, there is only one known area in the U.S., located in south Texas, where tick transmission of EP agents has previously occurred, but there are competent tick vectors present in other parts of the U.S. which could also cause natural transmission if EP-infected horses are introduced.
In areas where tick transmission has occurred, one method of control is through reducing the risk of horses being exposed to ticks by keeping pastures regularly mowed and by removing brush and weeds to reduce the level of tick infestations.
Chemical control methods are effective in reducing host exposure to ticks, especially when appropriate chemicals are applied at times and locations that will have the greatest impact on developmental stages of the tick, either on or off the host. The most common compounds used in areawide control are carbamate insecticides, natural pyrethrins and synthetic pyrethrins (often called pyrethroids).
In the U.S, EP agents have been spread more commonly by unhygienic practices that have resulted in the transfer of blood from an infected horse to another horse. This can be avoided by never reusing needles or syringes, by being certain that dental and tattoo equipment is thoroughly sanitized between horses, and that all surgical instruments and intravenous administration sets are sterilized prior to use. In addition, any horse intended to be used as a blood donor should be tested and be negative for EP.
- Use a new sterile needle and syringe for injections, whether into a vein or muscle or beneath the skin
- Clean and disinfect equine dental, tattoo and surgical equipment between horses
- Have any horse that will serve as a blood donor tested for EP
- Contact your veterinarian if your horse is sick and has signs of fever, reduced feed intake or lethargy
- Check with your State Animal Health Official if you need more specifics about EP
7. Where on my horse should I examine for ticks?
USDA guidance on the inspection of horses for ticks recommends a thorough and systematic examination. The following examination procedure, known as “scratching” for ticks, has been recommended:
- Begin at the horse’s head, examine both ears and palpate inside of each ear, examine the false nostrils visually and palpate each with the forefinger.
- Move to the forelock and examine the forelock, continuing down the mane to the withers.
- Examine the soft tissue between the bones that make up the lower jaw, using flattened hand and fingers, feeling for any unevenness of the skin.
- Examine the girth area of one side, visually and through palpation.
- Examine the posterior fetlock to the coronet of the front foot, visually and through palpation.
- Visually examine the udder/scrotum area on one side.
- Examine the tail and perineum, visually and through palpation.
- Examine the posterior fetlock to the coronet of the back foot, visually and through palpation.
- Visually examine the udder/scrotum of the other side.
- Examine the posterior fetlock to the coronet of the other back foot, visually and through palpation.
- Examine the posterior fetlock to the coronet of the other front foot, visually and through palpation.
- Perform hand hygiene after examining each animal.
8. What should I do if I find a tick on my horse?
Do NOT use any of the commonly described folk methods to remove ticks, such as applying petroleum jelly, fingernail polish, 70 percent isopropyl alcohol or a hot kitchen match to the attached tick. While these methods are thought to induce a tick to “detach” from an attachment site, they actually stimulate a tick to secrete more saliva, cause regurgitation, and introduce other tick-body secretions or excretions into the wound. These procedures increase the risk of tick-borne disease transmission and secondary infection around the bite location. The best method is to implement the following procedure:
- Using blunt curved forceps or a commercial tick-extraction tool, grasp the tick as close to the skin surface as possible and pull upward with a steady even pressure.
- Avoid squeezing, crushing or puncturing the tick’s body. As this can expel material into the attachment site while removing the tick from the host.
- Do not handle the tick with bare hands as ticks carry many kinds of disease on their body that can be harmful to people.
- Cleanse the bite site with soap and water.
Another method of tick removal is spraying the tick with pyrethrins or pyrethroids containing aerosol repellent, and then spraying again within one minute. Ticks will fall off after treatment.
To submit a tick for identification, place the tick in a container of alcohol (optimally 70 percent ethanol or 70 percent isopropyl) and send the specimen to a State, Federal, or University veterinary diagnostic laboratory with capabilities for tick identification.
9. If my horse tests positive for B. caballi or T. equi, the causative agents of EP, what do I do?
The options for positive horses in the U.S. are lifelong quarantine, euthanasia, export from the U.S., or enrollment in the EP treatment program with oversight by USDA.
Horses that test positive for EP MUST be quarantined. State and Federal animal officials will ensure that quarantine guidelines are being followed and are in place.
Euthanasia for positive horses is not required, but lifelong quarantine has led some owners to elect this option. Owners can work with their veterinarian and the animal health officials to determine if export from the U.S. is an option for the positive horse.
Most owners of EP-positive horses choose to enroll the horse in the treatment program. Although the EP treatment program has led to a successful outcome in most horses, the organisms can be refractory to treatment, and the carrier state can be difficult to clear. Treatment of EP-infected horses is performed by an accredited veterinarian with state/federal animal health official oversight. Contact your State or Federal animal health official to find out more about this option. Horses proven to be cleared of infection through the EP treatment program may be eligible for quarantine release in the future.
10. Will a negative test for EP become mandatory for horses that travel (i.e. show, trail, etc.) just as a negative Coggins test?
In making plans to travel with your horse, be sure to contact your veterinarian well in advance of your departure date to verify what is necessary testing and examination for each horse that will be traveling. Be sure to clarify with your veterinarian that all blood work being drawn will fulfill all required tests for interstate movement or entry to an event as one test does not cover all requirements. For example, a different test is administered for detection of Equine Infectious Anemia (EIA).
Currently, racetracks in at least 9 states have testing requirements for EP and other events and venues have periodically required EP testing the past and may do so again. Please consult with your State animal health office, the racetrack (or individual state racing commission office), show or other equine venue to confirm any EP testing or other health requirements. To find your State animal health official, please click here (updated link:
Testing policies may vary from state to state so be sure to check with your state veterinarian for the policies affecting your area.
Whenever transporting a horse interstate, check the requirements for the State of destination regarding what tests and examinations are required. Your veterinarian will need to collect samples and examine your horse to meet any requirements. Work closely with your veterinarian and let them know well in advance your plans to move your horse so that all requirements can be completed in advance of your departure date.
DID YOU KNOW? Ticks are commonly thought of as insects but are actually arachnids, such as scorpions, spiders, and mites. All members of this group have four pairs of legs as adults with no antennae. Ticks are among the most efficient carriers of disease agents because they attach firmly to a host when sucking blood, feeding slowly and may go unnoticed for a considerable amount of time while feeding. There are at least 850 tick species worldwide and approximately 85 tick species within the U.S.
Article reviewed in 2020 by Dr. Angela Pelzel-McCluskey.