Cystoisospora suis - the non-model model coccidium.

Cystoisospora suis, the cause of suckling piglet coccidiosis, is an intestinal protozoan pathogen of worldwide distribution and major economic and animal health significance in swine industry. It is closely related to cyst-forming, facultatively heteroxenic Coccidia like Toxoplasma gondii and Neospora caninum, but its biology resembles more that of the non-cyst-forming, homoxenic genus Eimeria. Lately, a unique in vitro cultivation system for C. suis was developed by which sporozoites infect monolayer cell cultures to produce merozoites which can in turn be propagated in a host-cell free system and develop into sexually differentiated gamonts, gametes and finally oocysts. This system has been used to produce and analyse developmental stages throughout the life cycle of C. suis. Transcriptomic, proteomic and secretomic data are now available, providing information for fundamental and applied research not only on this coccidian species but extrapolation to related parasites. In addition, antiparasitic compounds can be tested in this in vitro model, and further upscaling will provide a higher-throughput system for (pre-clinical) compound screening and in vitro efficacy testing for anticoccidial drugs, supporting the early detection of anticoccidial resistance in C. suis field strains. With these developments, C. suis can be considered a "non-model model" for the Coccidia, bridging the gap between the cyst-forming Sarcocystidae and the non-cyst-forming Eimeriidae, and between parasites of One Health relevance, such as T. gondii, and those members of the Coccidia that are of relevance in veterinary medicine and animal health.