Sarcocystidae

Sarcocystidae is a family of intracellular, tissue-dwelling protozoan parasites within the phylum Apicomplexa. It comprises several genera, including Sarcocystis, Besnoitia, Neospora, Hammondia, and Toxoplasma. Members have two-host life cycles with sexual reproduction in the intestinal epithelium of a definitive host (often a carnivore) and asexual development in the tissues of one or more intermediate hosts, where they form tissue cysts containing infectious stages.

Transmission typically occurs when an intermediate host ingests sporocysts or oocysts shed in the feces of the definitive host. Infections are common across livestock, wildlife, and companion animals and can cause disease ranging from muscular cyst formation to abortion or neurologic illness, depending on the species and host.

Toxoplasma gondii is the most widely studied species within the family and is zoonotic, capable of causing toxoplasmosis in humans and animals. Cats are the definitive hosts for T. gondii, with a broad range of intermediate hosts. Neospora caninum causes abortion in cattle, with dogs as the definitive host. Sarcocystis neurona is associated with equine protozoal myeloencephalitis in horses, transmitted via the opossum. Besnoitia besnoiti causes besnoitiosis in cattle, with transmission routes including mechanical vectors. Hammondia species are generally less pathogenic in their hosts but are important for understanding the biology of related parasites.

Taxonomically, the Sarcocystidae belong to the Apicomplexa, a diverse group of intracellular parasites that includes many medically and economically important pathogens.