What is Equine Piroplasmosis?

Equine Piroplasmosis (EP) is a tick-borne disease caused by the organism Theileria equi or Babesia equi that affects horses, donkeys, mules and zebras. The disease is transmitted via ticks or through mechanical transmission by improperly sanitized surgical, dental instruments, through the reuse of needles and syringes, or through the administration of contaminated blood products. EP is considered to be an exotic animal disease in New Zealand but it occurs in many other areas of the world.

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, surgical equipment). T. equi can be transmitted from an infected dam to her foal, although this route of transmission is uncommon. There is a lack of evidence to indicate if ticks present in New Zealand are capable of transmitting this disease between horses.

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 colour 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.

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 MPI 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 OIE recognizes a number of tests to screen for EP infection. In an outbreak situation, different types of tests are often needed to determine the infection status of a horse.

Most countries now require horses be tested for the infection before allowing them to enter.