Coccidia are a biological subclass of parasitic protozoa. Coccidia life cycle includes stages of development inside the host animal as well as in the external environment. At the internal stage the parasites affect intestinal mucosa and use mucosal cells for their reproduction. This stage causes coccidiosis. At the external stage the oocysts are highly resistant, and so control may not be easy.
Important coccidia in swine are Isospora suis, responsible for piglet coccidiosis.