COCCIDIA

A JOACHIM - Professor for Parasitology, Head of the Institute of Parasitology, DVM, DipEVPC, Institute of Parasitology, Vetmeduni Vienna, Veterinaerplatz 12, Vienna, A-1210  Austria

Coccidia are classified as protozoa in the class Coccidea, which belongs to the subphylum of the Apicomplexa. This large group is comprised exclusively of parasitic species that share specialised organelles to support their intracellular lifestyle, as well as a complex life cycle that includes phases of sexual and asexual development. The class Coccidea includes several orders that cause a variety of diseases, such as the Adeleida, the Cryptosporida (with the genus Cryptosporidium; several species of this group parasitize the intestinal tract of mammals and cause cryptosporidiosis but biological and biochemical differences set them apart from the coccidia in the strict sense) and the Eimeriida with two families. The Eimeriidae undergo temporary development in epithelial cells without major formation of resting stages, and the most important genus is Eimeria, which is a common cause of diseases of the digestive tract in poultry, ruminants and rabbits. The Sarcocystidae form tissue cysts and may undertake a host switch. Depending on the genus and species, they may cause a variety of diseases (toxoplasmosis, neosporosis). In current systematics, the genus Cystoisospora is a member of the Sarcocystidae since its members are capable of host-switching and formation of monozoic tissue cysts; however, the major clinical changes are related to their development in the intestinal epithelium of the final host. Mammalian Isospora species are now placed in the genus Cystoisospora.¹ The genera Eimeria and Cystoisospora both cause infections of the digestive tract with similar clinical and epidemiological characteristics and can be controlled with the same chemotherapeutics, so despite their now separate classification (Table 1) the disease they cause is still commonly described as coccidiosis in this chapter.

Table 1 Classification of the coccidia: the most important genera.^{2, 3} Synonyms and unverified taxa are not included.

Higher taxonomy
Phylum: Alveolata
Subphylum: Apicomplexa (syn. Sporozoa)
Class: Coccidea

dh: definitive host
ih: intermediate host

References

1. BARTA, J.R., SCHRENZEL, M.D., CARRENO, R. & RIDEOUT, B.A., 2005. The genus Atoxoplasma (Garnham 1950) as a junior objective synonym of the genus Isospora (Schneider 1881) species infecting birds and resurrection of Cystoisospora (Frenkel 1977) as the correct genus for Isospora species infecting mammals. Journal of Parasitology, 91, 726–727.
2. DEPLAZES, P., ECKERT J., MATHIS A., VON SAMSON–HIMMELSTJERNA G, ZAHNER, H., 2016. Parasitology in Veterinary Medicine. Wageningen: Academic Publishers.
3. DUSZYNSKI D.W, UPTON S.J. & COUCH, L, 2017. The Coccidia of the World. http://biology.unm.edu/coccidia/table.html