Sarcocystis fayeri-Induced Granulomatous and Eosinophilic Myositis in 2 Related Horses.

The research investigated two related horses suffering from chronic weight loss and abnormal gait, suspected to be caused by a parasitic infection from the protozoa Sarcocystis fayeri. This parasite is known to infect striated muscle in various species, typically without causing noticeable illness. However, in these cases it led to the formation of granulomas and significant muscle inflammation.

Research Subjects

• The two subjects of this research were genetically related paint mares, referred to as case Nos. 1 and 2. The horses were presented for evaluation due to chronic weight loss and abnormal gait, respectively.
• Notable clinical findings in both cases included marked persistent eosinophilia, a condition that denotes high levels of eosinophils or white blood cells. This is usually indicative of an ongoing inflammatory response to either parasites, allergens, or certain diseases. Both horses also had multiple intramuscular lateral thoracic masses.

Diagnostic Measures

• Histologic examination – The examination of the tissue samples from the horses was used to identify the nature of the health condition. This examination revealed eosinophilic granulomas and marked eosinophilic myositis.
• Parasite Identification – The tissue samples from the horses showed signs of intralesional Sarcocystis sp material, and adjacent muscle fibers contained intact protozoal cysts. These findings suggest that the horses were indeed infected by a parasite from the Sarcocystis species.

Findings

• Case No. 1 developed severe refractory muscle pain and recurrent esophageal dysphagia, a condition which makes it difficult for food and liquids to pass into the stomach.
• At necropsy, disseminated, grossly visible granulomas were present throughout all examined striated muscles. These granulomas are typically defense mechanisms that the body forms around foreign substances.
• Through nested polymerase chain reaction of the 18S rRNA gene, a type of diagnostic test, researchers found a >99% homology with Sarcocystis fayeri – confirming that this was the specific species of Sarcocystis that infected the horses.

Implications

• The researchers assert that Sarcocystosis – the condition of being infected by Sarcocystis fayeri – should be considered a rare cause of granulomatous eosinophilic myositis and choke in horses. Effectively, Sarcocystis fayeri infection can lead to serious muscular and respiratory symptoms despite typically being asymptomatic in many species.