page_title: Sarcocystis
section_title: Clinical: Nonhuman
hierarchical_section_title: Sarcocystis / Clinical: Nonhuman
caption_attribution_description: Sarcocystis sarcocysts within porcine skeletal muscle. Note the clearly defined striated border around the sarcocyst that helps differentiate it from Toxoplasma. The thin, black object in the right field is the microscope pointer.
context_page_description: Sarcocystis is a genus of parasites, the majority of species infecting mammals, and some infecting reptiles and birds.
  The lifecycle of a typical member of this genus involves two host species, a definitive host and an intermediate host. Often, the definitive host is a predator and the intermediate host is its prey. The parasite reproduces sexually in the gut of the definitive host, is passed with the feces, and ingested by the intermediate host. There, it eventually enters muscle tissue. When the intermediate host is eaten by the definitive host, the cycle is completed. The definitive host usually does not show any symptoms of infection, but the intermediate host does.
  About 130 recognized species are in this genus. Revision of the taxonomy of the genus is ongoing, and all the currently recognised species may be a much smaller number of species that can infect multiple hosts.
  The name Sarcocystis is dervived from Greek: sarx = flesh and kystis = bladder.
context_section_description: Four recognised species infect cattle: S. bovifelis, S. bovihominis (S. hominis), S. cruzi (S. bovicanis), and S. hirsuta. S. cruzi is the only species known to be pathogenic in cattle. Several clinical syndromes have been reported in connection with this parasite: eosinophilic myositis; abortions, stillbirths, and deaths in pregnant cows; two cases of necrotic encephalitis in heifers have also been reported. Typical clinical signs of acute bovine sarcocystosis are: anorexia, pyrexia (42°C or more), anemia, cachexia, enlarged palpable lymph nodes, excessive salivation, and loss of hair at the tip of the tail.
  Sheep may be infected by four recognized species of Sarcocystis: S. arieticanis and S. tenella (S. ovicanis) are pathogenic; S. gigantea (S. ovifelis) and S. medusiformis are nonpathogenic. Infection with these parasites is common in the US with over 80% of sheep examined showing evidence of infection. S. arieticanis and S. tenella both produce extraintestinal disease. Anemia, anorexia, ataxia, and abortions are the chief clinical signs. Myositis with flaccid paralysis has been reported as a consequence of infection. Ovine protozoan myeloencephalitis is a recognised syndrome that may occur in outbreaks. The usual pathological findings in such cases are multifocal spinal cord white matter oedema and necrosis, glial nodules and mild to moderate nonsuppurative encephalomyelitis. The diagnosis may be established finding protozoan bodies (12.7–23.0 μm) that stain immunocytochemically for Sarcocystis epitopes. 
  Four recognised species infect pigs: S. medusiformis, S. meischeriana (S. suicanis), S. porcifelis, and S. suihominis. S. porcifelis is pathogenic for pigs causing diarrhea, myositis and lameness.
  Five species infect horses: S. asinus, S. bertrami, S. equicanis, S. fayeri, and S. neurona (S. falcatula). All use canids as definitive hosts; transplacental infection has also been reported. S. neurona causes equine protozoal myeloencephalitis. Exposure to this parasite appears to be common in the United States, with serological surveys indicating that 50–60% percent of all horses in the Midwest United States have been exposed to it. Clinical signs include gait abnormalities including ataxia, knuckling, and crossing over. Muscle atrophy, usually unilateral, may occur. The lesions are typically focal. Brain stem involvement is common. Depression, weakness, head tilt, and dysphagia also occur.
  S. fayeri may cause myositis in horses.
  Fatal infection of an alpaca (Lama pacos) with an unnamed species has been reported. Findings included disseminated eosinophilic myositis, abortion, and haemoabdomen. The myositis was associated with hameorrhage, necrosis, and degeneration. Infection by S. tilopodi of muscle tissue in the guanaco has been reported.
  S. hemionilatrantis infects mule deer. Death from experimental inoculation has been reported.
  These parasites can also infect birds, producing three different clinical forms: an acute pulmonary disease, muscular disease, and neurological disease. Symptoms include lethargy, shortness of breath, tail bobbing, yellow-tinted droppings, and sudden death. The presence of the cysts in the muscle of wild birds is known as "rice breast".
caption: Sarcocysts within pig skeletal muscle: Note the readily visible striated border.
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