Species of protozoa in the family Sarcocystidae usually have an obligate 2-host life cycle that predominantly takes place in the intestinal tract. However, atypical or aberrant migrations can occur. Life cycles are species-specific, but in general, a definitive host ingests an infective form, an enteroepithelial cycle of sexual and asexual reproduction takes place in the intestinal tract, and unsporulated oocysts are shed intermittently in feces. The oocysts sporulate in the environment, becoming infective to intermediate hosts. After ingestion, the organisms replicate in the intestine and spread to other tissues in blood and lymphatic vessels. The organisms then persist in the tissues, primarily as cysts. And the life cycle continues.
Infections with Hammondia spp have been considered nonpathogenic, but H heydorni is prevalent in dogs with diarrhea. The life cycle of H heydorni is not well understood, but both unsporulated and sporulated oocysts have been found in the feces of dogs with natural H heydorni infections. Intermediate hosts are reported to be small rodents and ruminants. Several Sarcocystidae (Sacrocystis and Neopspora in dogs, Toxoplasma in cats) have been reported to cause hepatitis, although the mechanism is unknown. The clinical presentation includes lethargy, anorexia, and fever with markedly increased liver enzymes. This nonspecific presentation is similar to that of bacterial or toxic hepatopathy, and there may not be other signs that suggest a protozoal infection.
Links to sections in MVM:
Overview of Hepatic Disease in Small Animals
Enzyme Activity in Hepatic Disease in Small Animals
Overview of Sarcocystosis
References:
Irvine KL, Walker JM, Friedrichs KR. Sarcocystid organisms found in bile from a dog with acute hepatitis: a case report and review of intestinal and hepatobiliary Sarcocystidae infections in dogs and cats. Vet Clin Pathol. 2016 Mar;45(1):57-65. doi: 10.1111/vcp.12330
PubMed abstract: https://www.ncbi.nlm.nih.gov/pubmed/26870918
Dubey JP, Sykes JE, Shelton DG, et al. Sacrocystis caninum and Sarcosystis svanai n. spp. (Aapicomplexa: Sarcocytisdae) associated with severe myositis and hepatitis in the domestic dog (Canis familiaris). J Eukaryot Microbiol. 2015 May-Jun;62(3):307-17. doi: 10.1111/jeu.12182
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