Sarcocystosis in Horses

Sarcocystosis in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

Most common symptoms

Collapse / Difficulty Walking / Lethargy / Seizures / Shaking / Weight Loss


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Most common symptoms

Collapse / Difficulty Walking / Lethargy / Seizures / Shaking / Weight Loss

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Sarcocystosis in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

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What are Sarcocystosis?

S. neurona is one type of sarcocystosis spp and the species has hundreds of variations. While there is a possibility of symptoms being present, in same cases, horses may be asymptomatic. Your horse may contract this parasite by ingestion of either the eggs or the tissues of an infected animal. Your horse may present with neurological symptoms that could mimic many other neurological disorders and diseases. This may make it difficult to distinguish what is causing your horse’s problems. A veterinary visit is warranted in order to determine the exact cause of the symptoms.

Sarcocystosis in horses is caused by the parasite Sarcocystis neurona and is the most common cause of EPM (equine protozoal myeloencephalitis) in horses. Your horse may present with multiple symptoms such as weight loss, decreased appetite, sweating, and mild depression.

Symptoms of Sarcocystosis in Horses

  • Depression -  Your horse may not have his typical behavior and seem lethargic 

  • Head tilt – Your horse may begin to tilt his head to one side frequently with no explanation
  • Seizures 
  • Facial paralysis – His facial muscles may become paralyzed and he may have difficulty with eating or drinking 
  • Vision defects 
  • Incoordination – Your horse may have difficulty walking and coordinating his movements 
  • Weakness
  • Muscle loss, particularly in hind limb
  • Sensory loss
  • Weight loss
  • Appetite loss
  • Sweating
  • Loss of reflex


Three recognized protozoan species that impact horses are: 

  • S. neurona is the cause of EPM and typically presents with neurological issues
  • S. fayeri is rare in horses but presents with muscle atrophy, depression and other symptoms
  • S. bertrami has never been found in the U.S. but has been found in Europe

Causes of Sarcocystosis in Horses

The cause of your horse contracting sarcocystosis is the result of his ingesting the parasite. This can be done via 2 methods.

  • Ingestion of another animal who is infected
  • Ingestion of the protozoan eggs  (can occur in the environment, can be found in your horse’s food after being contaminated by other animals
  • Opossums carry the parasites; if they are around your horse’s feed or paddock he runs a higher risk of becoming infected

Diagnosis of Sarcocystosis in Horses

Diagnosis of the parasite will need to be made by your veterinarian and will require testing to be done. Clinical signs such as loss of coordination, depression, weight loss and seizures can be indicative of many illnesses and diseases. The veterinarian will need to rule out other conditions that can present the same; the physical examination, serum biochemistry, and a possible tissue biopsy will point to the diagnosis of sarcocystosis. However, most often the presence of the parasites are confirmed at necropsy of a deceased animal.


Treatment of Sarcocystosis in Horses

In the event your horse is diagnosed with sarcocystosis, your veterinarian will lay out a plan of treatment options for him. There are multiple medications that can be prescribed: sulfonamides, sulfadiazine, diclazuril, pyrimethamine and toltrazuril have all been used with success to treat the parasite. Your veterinarian may also recommend that your horse have paddock rest for up to 30 days post diagnosis. Anti-inflammatory medications have been used as well to help with ongoing pain or discomfort. 

The best treatment is prevention of your horse being infected by the parasite. This can be done by keeping your horse’s area clean and free of raw meat, keeping his food container’s close and covered to prevent contamination by rodents or other animals. Lastly, keeping wild animals (particularly the opossum) out of the areas where your horse is kept will also help to prevent the parasite infection.

Recovery of Sarcocystosis in Horses

Your horse may need to be on medication and have rest for up to 30 days if not more; therefore, his recovery may take some time. It will be important to prevent further exposure of your horse to the parasite by taking precautions once you are aware.

Your veterinarian may require follow up to ensure your horse does not have any ongoing issue related to his infection of the parasite. It will also be important to continue being mindful of any possible signs and symptoms your horse may exhibit in the future.

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