Equine piroplasmosis is a disease transmitted by ticks and caused by blood protozoa that produce alterations derived from the destruction of red blood cells and problems circulatory, being able to cause from a mild disease to a hyperacute one that derives in the death of the animal. Most of the symptoms are non-specific and variable depending on the severity of the disease, which in turn will depend on the parasite load and immunity, which will be largely determined by the area where the horse is infected.
What is equine piroplasmosis?
Equine piroplasmosis is one of the most common diseases in horses. It is a parasitic disease transmitted by ixodid ticks of the genus Dermacentor, Hyalomma and Rhipicephalus, which affects horses, mules, donkeys and zebras (these ticks act as a major reservoir of the disease in Africa). Another mode of transmission can be iatrogenic through surgical utensils, contaminated syringes or needles, and blood transfusions from parasitized animals. It is a disease that causes damage mainly to the red blood cells of horses, producing symptoms derived from hemolytic anemia due to their rupture, in addition to producing clinical signs various non-specific and, in some cases, circulatory alterations that end up with the animal in shock due to low blood volume (decrease in the animal's blood volume).
The vast majority of the world's equids are found in disease-endemic (i.e. disease-bearing) areas, which are tropical, subtropical, and temperate zones of southern Europe, Africa, Asia, the Caribbean, South America, Central America and some parts of the southern USA. The main importance of equine piroplasmosis is the restriction in the movement, competitions and trade of horses around the world, being a particularly important risk in areas where it is not endemic.
What causes equine piroplasmosis?
Piroplasmosis in horses is caused by the hematic protozoa that belong to the order Piroplasmida and the phylum Apicomplexa, specificallyTheileria equi (theileriosis) and/or Babesia caballi (babesiosis). B. caballi parasitizes only the red blood cells of horses, while T. equi also parasitizes white blood cells, specifically, it first invades lymphocytes and at around nine days parasitizes red blood cells. It is a disease that can occur at any time of the year if mixed infection or theileriosis occurs exclusively, since cases of babesiosis appear only in summer and winter.
The name piroplasmosis is due to the pear-shaped shape that the parasites manifest inside the red blood cells of infected horses. Horses that have passed the disease can be carriers of B. caballi for a few years, while T. equi for life, acting as sources of infection for ticks that, in turn, will bite other horses, transmitting the disease. T. equi can also be transmitted transplacentally in pregnant females ending with fetal death, abortion or acute infection in newborns.
Equine piroplasmosis symptoms
Both parasites target the horse's red blood cells and as a consequence of their multiplication in them, a hemolytic anemia is produced due to its rupture, being more serious the greater the parasitic load of the animal, which is usually more serious in theileriosis, and can cause hemolysis greater than 40%.
The acute disease is the most common and is characterized by clinical signs resulting from hemolysis such as:
- Anemia.
- Tissue anoxia (lack of oxygen).
- Swollen abdomen.
- Tachycardia (increased heart rate).
- Tachypnea (increased breaths per minute).
- Fever (greater than 40ºC).
- Increased sweating.
- Pale or yellow discoloration (jaundice) of the mucous membranes.
- Anorexy.
- Weightloss.
- Depression.
- Weakness.
- Constipation, with small, dry stools.
- Thrombocytopenia (decreased total platelet count).
- Small hemorrhages (petechiae or ecchymoses).
- Hemoglobinuria (loss of hemoglobin in the urine, giving the urine a reddish color).
- Bilirubinemia (increased bilirubin in the blood due to hemolysis).
Furthermore, in equine babesiosis they can predominate over hemolytic anemia alterations in the blood vessels with obstruction of the circulation of the brain, thrombi in lungs, kidneys and liver that alter their proper functioning, as well as the release of parasitic enzymes that end with vasodilation, increased permeability of blood vessels and shock due to blood loss that can end the life of our horse.
In the peracute cases, the horse usually dies. Fortunately, these are not the most frequent cases. In cases of chronic disease, the symptoms of piroplasmosis in horses are:
- Inappetence.
- Low exercise tolerance.
- Weightloss.
- Transient fever.
- Enlarged spleen (palpable by rectal exam).
Diagnosis of equine piroplasmosis
In the event of a suspected case of equine piroplasmosis, because it is a notifiable disease that appears on the list of the OIE (World Organization for Animal He alth), official veterinarians must notify the OIE of the suspicion of the disease in order to apply the necessary guidelines and take samples to detect it.
Clinical Diagnosis
A horse with pale mucous membranes or jaundice, weak, with little tolerance for exercise and that has a fever makes us quickly think of hemolytic anemia and then of this disease, especially if we are in an endemic area or the horse has traveled to one. In addition, if a blood test is performed, parameters indicative of this process will be seen, such as an increase in eosinophils (since these white blood cells increase in the face of parasitic diseases), a decrease in hematocrit (volume of red blood cells in the total blood), hemoglobin (a protein in red blood cells that carries oxygen) and platelets.
Due to the non-specificity of some symptoms, it must be differentiated from other equine diseases that can cause the same symptoms such as:
- Equine infectious anemia
- Poisoning
- African horse sickness
- Leptospirosis
- Trypanosomosis
- Erhlichiosis
- Autoimmune diseases causing hemolytic anemia
Lab Diagnosis
To diagnose the disease, you must take a blood sample from the suspected horse to perform direct tests to detect parasites or indirect tests to find the antibodies once the horse has mounted an immune response. The direct tests are:
- Blood smear (view a drop of blood under a microscope): this is the traditional, simple, economical and fast method, performed when the horse has a fever. The inclusions of the parasites in the horse's red blood cells will be observed. However, if the parasite load is low, they are sometimes not seen and can be diagnosed as negative when it really is not.
- PCR: when the horse has a fever, if combined with the blood smear, the efficiency to detect the parasite is more reliable.
On the other hand, the indirect tests correspond to the following:
- Complement fixation test: This has been the official test for quite some time, being more useful to rule out the disease than to confirm it.
- Indirect immunofluorescence: detects infections when time has passed and the horse has created high antibody titers. It is useful for detecting carrier horses.
- Indirect ELISA: also detects carriers and animals with antibodies against these parasites well.
Treatment of equine piroplasmosis
When this disease appears, the equine veterinarian must apply a treatment to alleviate the symptoms or symptomatic and a specific antiparasitic to kill these protozoa.
Symptomatic treatment
Treatment to relieve the symptoms of piroplasmosis in horses consists of:
- Blood transfusion if anemia or bleeding is severe.
- Antipyretics for fever.
- Fluid therapy to control dehydration.
- Supplements of iron, B vitamins and folic acid to strengthen the bone marrow and the immune system.
Specific treatment
To treat equine piroplasmosis specifically it is necessary to use:
- Imidocarb dipropionate: it is the main antiparasitic used for equine piroplasmosis, it is very effective for babesiosis, with two doses of 2-3 mg/kg by intramuscular injection in 24 hours, and for theileriosis with a dose of 4 mg/kg by the same route four times every 72 hours. If this drug is used, atropine sulfate should be used to avoid side effects such as salivation, colic, or increased intestinal motility.
- Diminacene aceturate: dose of 4-5 mg/kg daily intramuscularly until symptoms disappear or single dose 11 mg/kg by the same route is effective for both protozoa.
- Parvaquone: at 20 mg/kg intramuscularly it is effective against T. equi
- Buparvaquone: at 5 mg/kg intramuscularly it is also effective against theileriosis.
Only a specialized veterinarian is qualified to prescribe medications for piroplasmosis and determine the proper dosage. Never self-medicate your horse because you could worsen his condition
Prevention of piroplasmosis in horses
The prophylaxis of this disease is based on the therapy of infected horses, the control of ticks as a vector of the disease (by means of acaricides, frequent searches in the animal and elimination of those found) and the limitation of movements of infected horses when there is no effective vaccineIn non-endemic areas, the entry of horses from endemic regions must be restricted (in those cases that are going to enter, it is required that they do not have symptoms, that they be negative to antibody tests and anti-miticide treatment prior to movement), as well as monitor especially transfusions and other iatrogenic routes of disease transmission.
