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Piroplasmosis is a common tick-borne disease of horses. In some cases, the horse may remain asymptomatic, but in the most severe forms, piroplasmosis can cause the death of the horse within 48 hours.
Piroplasmosis is transmitted by ticks that carry the 2 protozoa (single-celled microorganisms) responsible for the disease: Babesia caballi or Theileria equi. This parasitic disease of the horse is transmitted when a tick bites, through its saliva. It is only transmitted through the saliva of ticks, so affected horses cannot infect each other. It can also affect other animals, as well as humans. Most often, horses are healthy carriers of the disease and may not develop symptoms for a long time. However, piroplasmosis can be triggered when the protozoa start to multiply in the horse’s blood and thus cause symptoms of fatigue.
Ticks are particularly prevalent in spring and autumn, in undergrowth or at the edge of forests, so you should be particularly vigilant and inspect your horse regularly if it is living in a meadow or out walking in the forest.
Piroplasmosis can be difficult to diagnose because in its mildest form, the horse may simply show symptoms of fatigue, weight loss or loss of appetite, which can be symptoms of many other horse diseases.
In its most acute forms, piroplasmosis can affect the foal in particular (this is known as neonatal piroplasmosis), which will present with anaemia, fever and yellow discolouration of the mucous membranes (which will also be scattered with small red spots). In the case of adult horses, the symptoms of piroplasmosis are numerous: a fever of more than 40° (causing the horse to sweat a lot), a sharp drop in energy, anorexia (due to a loss of appetite), yellow discolouration or congestion of the mucous membranes, oedemas (on the limbs or over the eyes), the presence of blood in the urine, an increase in the heart and/or breathing rate, dehydration or even a recumbent position of the horse (which is too weak to get up).
In order to diagnose piroplasmosis, a blood smear will be observed under a microscope in the clinic to show the piroplasms in the red blood cells. The most commonly used treatment is imidocarb. In the case of infection by the protozoan Babesia caballi, your veterinarian will give 2 injections of imidocarb 24 hours apart. In the case of infection with Theileria equi, the treatment will consist of 4 injections at 72 hour intervals, as this form is more resistant. However, eradication of piroplasmosis is not guaranteed at the end of the treatment, even if the clinical signs may disappear. It is therefore important to be aware of potential relapses. Beware also of the side effects of imidocarb, which can cause colic. As the treatment is rather heavy for the horse, it is important not to hesitate to supplement it with vitamins, minerals and amino acids in order to stimulate the production of red blood cells.
In the most severe cases, the horse may be placed on a drip to rehydrate it or be transfused if the anaemia is too pronounced. Following treatment, the horse should be rested for at least one month.