Genus Sarcocystis

Genus Sarcocystis: Classification, Morphology and Important Species

Sarcocystis is a genus of obligate intracellular protozoan parasites belonging to the phylum Apicomplexa. These parasites have an indirect life cycle involving both herbivorous intermediate hosts and carnivorous definitive hosts. Sarcocystis species are of significant veterinary importance because they can cause economic losses in livestock and, in some cases, infect humans.

This article provides concise notes on the classification, morphology, life cycle, and important species of Sarcocystis, making it a useful resource for veterinary students and professionals.

Taxonomical Classification

• Kingdom: Protista
• Phylum: Apicomplexa
• Class: Conoidasida
• Subclass: Coccidiasina
• Order: Eucoccidiorida
• Family: Sarcocystidae
• Genus: Sarcocystis

Parasite Overview

Members of the genus Sarcocystis are obligate heteroxenous parasites. Herbivores act as intermediate hosts, while carnivores are the definitive hosts in which sexual reproduction occurs.

Asexual reproduction (merogony) occurs in the endothelial cells of blood vessels in the intermediate host. However, the last-generation meronts found in the striated and cardiac muscles, and rarely in the brain, are called sarcocysts.

The sarcocysts may be either microscopic or visible to the naked eye, depending on the species and stage of development. Large sarcocysts are called Miescher’s tubules. Initially, the sarcocyst contains metrocytes (promerozoites) and, upon maturation, bradyzoites.

The oocysts develop in the lamina propria of the small intestine and sporulate there, a process called endosporogony. The oocysts may rupture in the intestine; therefore, sporocysts, rather than intact oocysts, are sometimes passed in the feces of the definitive host. Sporocysts of Sarcocystis may often be mistaken for oocysts of Cryptosporidium.

Sarcocystis Species

The following species are frequently reported in domestic animals:

• Sarcocystis cruzi
  • Intermediate host (prey): Bovine
  • Definitive host (predator): Dog
• S. bovifelis
  • Intermediate host (prey): Bovine
  • Definitive host (predator): Cat
• S. hominis
  • Intermediate host (prey): Bovine
  • Definitive host (predator): Human
• S. tenella
  • Intermediate host (prey): Ovine
  • Definitive host (predator): Cats