Sarcocystis spp

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Cysts of Sarcocystis under light microscopy[1]

Sarcocystis spp are a relatively common ampicomplexan protozoan parasite of dogs in countries where they are endemic and can cause gastrointestinal and systemic disease.

Prevalence rates in some countries can range from 5 - 15% of urban dogs[2][3].

Species which are pathogenic to dogs include:

  • sarcocystis cruzi
  • Sarcocystis tenella
  • Sarcocystis wenzeli [4]
  • Sarcocystis camelicanis[5]
  • Sarcocystis neurona

The life cycle, like that of Hammondia hammondi, this parasite has an obligatory two-host life history but sexual reproduction only occurs in the definitive host, where sporogony is completed. Dogs become infected by eating infected flesh of other hosts such as birds or other herbivores. Ingestion of bradyzoites in uncooked meat or wild game results in oocysts being released in the dog intestine, where they sporulate and penetrate the intestinal wall to migrate via the lymphatics to skeletal muscle[6]. Rare cases of migration to the liver and brain have been reported.

Fully sporulated oocysts and sporocysts are passed in the dog feces[7]. The prepatent period is relatively short, at about 12 days.

Dogs infected with this parasite are often asymptomatic, but acute myositis has been reported associated with translocation of the parasite from teh gut to the skeletal muscle. These dogs usually present with fever, muscle pain, lymphopenia, thrombocytopenia, and increased serum alanine aminotransferase (ALT) activity[8].

Sarcocystis neurona encephalitis[9] and hepatitis[10] have been reported in dogs. Protozoal polyradiculoneuritis and Sarcocystis encephalitis presents as hindlimb paresis, aggression and hyperesthesia.

Diagnosis is based on coprological examination for eggs[11], ELISA and PCR assays and identification of parasite on tissue biopsy samples under light microscopy.

A differential diagnosis would include other protozoan parasites such as Toxoplasma gondii and Neospora caninum.

Empirical treatment is clindamycin and decoquinate but severely affected dogs may die due to extensive inflammatory changes in the target organs.


  1. Stanford Uni
  2. Nonaka N et al (2011) Coprological survey of alimentary tract parasites in dogs from Zambia and evaluation of a coproantigen assay for canine echinococcosis. Ann Trop Med Parasitol 105(7):521-530
  3. Beiromvand M et al (2012) Prevalence of zoonotic intestinal parasites in domestic and stray dogs in a rural area of Iran. Prev Vet Med Oct 5
  4. Chen X et al (2012) Infections with Sarcocystis wenzeli are prevalent in the chickens of Yunnan Province, China, but not in the flocks of domesticated pigeons or ducks. Exp Parasitol 131(1):31-34
  5. Abdel-Ghaffar F et al (2009) Life cycle of Sarcocystis camelicanis infecting the camel (Camelus dromedarius) and the dog (Canis familiaris), light and electron microscopic study. Parasitol Res 106(1):189-195
  6. De Meireles GS et al (2008) Evaluation of small intestine and mesenteric lymph nodes of dogs (Canis familiaris) experimentally infected by Sarcocystis cruzi (Hasselman, 1923) Wenyon, 1926 (Apicomplexa: Sarcocystidae). Rev Bras Parasitol Vet 17(1):331-334
  7. Bowman, DD (2009) Georgis' parasitology for veterinarians. 9th edn. Elsevier Saunders, Missouri. pp:104-105
  8. Sykes JE et al (2011) Severe myositis associated with Sarcocystis spp. infection in 2 dogs. J Vet Intern Med 25(6):1277-1283
  9. Cooley AJ et al (2007) Sarcocystis neurona encephalitis in a dog. Vet Pathol 44(6):956-961
  10. Allison R et al (2006) Fatal hepatic sarcocystosis in a puppy with eosinophilia and eosinophilic peritoneal effusion. Vet Clin Pathol 35(3):353-357
  11. Sager H et al (2006) Incidence of Neospora caninum and other intestinal protozoan parasites in populations of Swiss dogs. Vet Parasitol 139(1-3):84-92