Sarcocystis fayeri–Induced Granulomatous and Eosinophilic Myositis in 2 Related Horses

Abstract

This report describes 2 genetically related paint mares, case Nos. 1 and 2, presented to the Oklahoma State University Boren Veterinary Medical Teaching Hospital for chronic weight loss and abnormal gait, respectively. Notable findings in both cases included marked persistent eosinophilia and multiple intramuscular lateral thoracic masses. Histologic examination of masses revealed eosinophilic, centrally necrotic granulomas and marked eosinophilic myositis. Granulomas in case No. 1 also contained intralesional Sarcocystis sp material, and adjacent muscle fibers contained intact protozoal cysts. Case No. 1 developed severe refractory muscle pain and recurrent esophageal dysphagia. At necropsy, disseminated, grossly visible granulomas were present throughout all examined striated muscles. Nested polymerase chain reaction of the 18S rRNA gene revealed >99% homology with Sarcocystis fayeri. Sarcocystis spp are apicomplexan protozoa that infect striated muscle of many omnivorous species, typically without inciting clinical disease. Sarcocystosis should be considered a rare cause of granulomatous eosinophilic myositis and choke in horses.

Sarcocystis infection in red deer (Cervus elaphus) with eosinophilic myositis/fasciitis in Switzerland and involvement of red foxes (Vulpes vulpes) and hunting dogs in the transmission

“…Several studies provided evidence for a causal association between Sarcocystis spp. infection and eosinophilic myositis in different animal species such as cattle ( Gajadhar et al, 1987 ; Wouda et al, 2006 ; Aráoz et al, 2019 ; Jensen et al, 1986 ; Vangeel et al, 2013 ), sheep ( Jensen et al, 1986 ), horses ( Herd et al, 2015 ) and alpacas ( La Perle et al, 1999 ), including the experimental reproduction of the lesions in cattle ( Vangeel et al, 2012 ). However, the details of the pathological mechanisms of sarcosporidiosis causing eosinophilic myositis/fasciitis and grey-greenish tissue discolouration are mostly unknown.…”

“…Sarcocystis antigens (lysed sarcocysts) inoculated intramuscularly in cattle were shown to induce local lesions at the injection site, characterized by massive infiltration of eosinophilic granulocytes, reactive macrophages, T-cells and B-cells, resembling natural eosinophilic myositis ( Vangeel et al, 2012 ). Besides, a genetical predisposition of some individual animals was also suggested to play a role in the pathogenesis of eosinophilic myositis ( Herd et al, 2015 ; Granstrom et al, 1989 ). This hypothesis would be in agreement with the low prevalence of eosinophilic myositis despite the high prevalence of Sarcocystis infection in certain animal species like cattle ( Aráoz et al, 2019 ; Vangeel et al, 2013 ).…”

“…Even though the Sarcocystis species found in red deer are not regarded as zoonotic, the affected carcasses can be declared as unfit for human consumption due to the extensive pathological changes ( Stephan et al, 2012 ). Association of Sarcocystis infection with greenish discolouration of the carcasses due to eosinophilic myositis/fasciitis has been described in several animal species including cattle, sheep, horses and South American camelids ( Gajadhar et al, 1987 ; Wouda et al, 2006 ; Aráoz et al, 2019 ; Jensen et al, 1986 ; Vangeel et al, 2013 ; Herd et al, 2015 ; La Perle et al, 1999 ), but this was considered infrequent in cervids ( Stephan et al, 2012 ).…”

Sarcocystis myositis and vitamin E deficiency in a Gypsy Vanner stallion suspected of having equine motor neuron disease

“…Anaemia, also present in the described case and herd mates, is a common clinicopathological feature of sarcocystosis (Fayer and Dubey 1982; Herd et al . 2015). Although the authors could not identify normal haematocrit reference ranges for the Gypsy Vanner breed specifically, all measured values were considered below the normal adult equine range.…”

“…The reason why inflammation develops in association with S. fayeri in rare cases is unclear, but has been proposed to be due to a secondary type I hypersensitivity reaction similar to that seen in cattle with granulomatous and eosinophilic myositis associated with Trypanosoma cruzi infestation (Herd et al . 2015; Díez de Castro et al . 2016).…”