What are Piroplasmosis?
Equine piroplasmosis (EP) is a blood-borne disease that infects equids including horses, donkeys, mules and zebras. Within the United States alone, 85 species of these arachnids exist, many that effectively transmit disease to susceptible mammals, birds, reptiles, and amphibians. Equine piroplasmosis is a particularly perilous disease that forces its equine hosts into quarantine or death. Blood from infected horses is consumed by ticks and then transferred to uninfected equids through the feeding process. Two parasites, Theileria equi or Babesia caballi (T. equi and B. caballi), cause this disease, but since EP is blood-borne, it is also transmitted by way of contaminated needles and syringes, or surgical, dental or tattoo instruments left unsanitized between horses. Other means of transmission include ticks spreading the parasites to other generations of ticks, as well as mares passing the organism to foals during the gestational period.
Ticks are biological vectors (tick-vectors), meaning they host parasites such as Theileria equi or Babesia caballi. The parasites reproduce within the vector, which then latches onto an uninfected horse for a period of time typically determined by the organism. While the disease is not contagious, horses typically live in social groups or in equid-populated settings such as barns, shows, or tracks. These environments are ideal settings for opportunistic parasites in search of food or mates, and unfortunately, enable the efficient spread of infection. Currently, horses are specifically tested for such diseases before being admitted into tracks or show areas. Visible symptoms are unreliable because an infected horse may have yet to develop or exhibit signs of equine piroplasmosis. Post-bite, the babesia takes one to four weeks to incubate, leaving an infected horse without visible signs of the disease. Throughout this period, the horse is capable of infecting other horses. EP-positive horses in the U.S. are placed lifelong quarantine, euthanized, exported from the U.S. or enrolled in a research program managed by the USDA.
Currently, organizations such as the U.S. Department of Agriculture state that the risk of EP transmission in the United States is low. However, due to environmental changes, or the possibility of entrance of international horses onto U.S. soil, some researchers suggest that these claims are unreliable. Isolated outbreaks have occurred, including fourteen horses that tested positive for EP in California since 2014. Missouri and Florida have had small outbreaks, but these were traced to blood transfusions and poor sanitation of equipment between horses. If there is a concern about tick-bites on your horse, you are strongly encouraged to procure rapid veterinary treatment. A horse with a blood-borne infection places other equines at marked risk.
Equine piroplasmosis (EP) is a blood-borne disease that transmits to horses, donkeys, mules and zebras during the feeding process of tick-vectors.
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Symptoms of Piroplasmosis in Horses
- Loss of appetite
- Breathlessness, wheezing or labored breath
- Rapid weight loss
- Jaundiced mucous membranes
- Swollen abdomen (fluid accumulation)
- Swollen limbs
- Roughened coat
Causes of Piroplasmosis in Horses
- EP is a blood-borne disease caused by the bites of tick-vectors already infected by parasites, Theileria equi or Babesia caballi (T. equi and B. caballi)
- EP is also transmitted by way of contaminated needles and syringes, or surgical, dental or other mechanical instruments unsanitized from horse to horse
- Other means of transmission include ticks spreading the parasites to other generations of ticks
- Mares may pass the organism to her foal during the gestational period
Diagnosis of Piroplasmosis in Horses
Lab testing is necessary to make a definitive diagnosis since symptoms of EP mirror many other diseases. Confirmation of tick-borne infection is essential. The purpose of the testing is to isolate the parasite in the horse’s blood, but detection is not always possible.
Due to its classification as an exotic illness in the U.S., any animal suggestive of a diagnosis of EP or blood-borne infection must be reported to a veterinarian, who will then alert state or federal animal health officials. The USDA has developed different of types of testing that aim to find antibodies to the parasite in the blood. One such test is the cELISA (competitive enzyme-linked immunosorbent assay), which is the standard test for screening for EP infection. This test is now used to clear horses for competition. A separate test aims to find parasitic organisms such as Theileria equi or Babesia caballi. Combined, this battery of specialized testing is an effective way to isolate horses with EP.
Treatment of Piroplasmosis in Horses
Currently, there is no vaccine for EP; however, a treatment has been developed for Theileria equi infections. While this is a positive step, horses undergoing this drug treatment are still required to be quarantined within a state or federally-approved program under the close observation of USDA veterinarians. Horse owners are responsible for all expenses. Studies have shown that some horses who undergo a long-term quarantine treatment program initiated in 2013, which includes enrollment in the USDA research protocol have qualified for release after completion of the protocol. Despite these advances, there is an ongoing need for treatment for tick-borne infections and disease.
Recovery of Piroplasmosis in Horses
Since horses positive for EP are often quarantined for life by a USDA research program or euthanized, it’s more constructive to focus on tick prevention and education. Some horses, however, may remain in quarantine only until multiple retests show a lack of the organisms. At this point, horse owners are responsible for further testing and are also required to place a microchip in the horse. Horse owners are encouraged to ask a veterinarian how to check for ticks by using a specific process known as scratching. Bite areas often reveal localized swelling and irritation to the skin. It’s important to notice if there are any signs of infection at the site of the tick bite.
An immediate way to lessen instances of tick-borne infection is to reduce exposure to tick-favorable environments. Environmental treatment and care (such as mowing pastures and removing tall brush and weeds) is one way to lessen the chance of tick bites. Using unsterilized equipment places horses at significant risk for contamination, so all mechanical equipment must be disposed of or sterilized between horses. Practicing stringent hygiene reduces opportunities for the transfer of infected blood.