re-evaluation of asynchronous asexual development of cystoisospora canis in intestines of dogs

Authors: Dubey, Jitender; LINDSAY, D.S. - Virginia-Maryland Regional College Of Veterinary Medicine (VMRCVM)

Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2018
Publication Date: 2/1/2019
Citation: Dubey, J.P., Lindsay, D. 2019. re-evaluation of asynchronous asexual development of cystoisospora canis in intestines of dogs. Journal of Parasitology. 105:25-28. https://doi.org/10.1645/18-131.
DOI: https://doi.org/10.1645/18-131

Interpretive Summary: Toxoplasma, Neospora, Sarcocystis, and Cystoisopora are related coccidian parasites that cause severe illness in livestock and companion animals. Oocyst is the environmentally resistant stage passed in feces of the definitive hosts. While Toxoplasma and Neospora have wide host range, Cystoisospora are more host specific. Cystoisospora canis is a pathogenic coccidian of dogs with many aberrant/paratenic hosts. Its life cycle is not fully known. Here, authors describe asexual cycle (meronts,schizonts) of C. canis using archived specimens; no new experiments were performed in dogs. These results will be of interest to parasitologists and veterinarians in diagnosis of coccidiosis in dogs.

Technical Abstract: The coccidian parasite Cystoisospora canis (syn. Isospora canis) can cause clinical disease in dogs. Three generation of schizonts have been reported in the small intestine of dogs before oocysts are excreted 9-11 days post inoculation (PI). Here, we re-evaluated asexual development of C. canis in 2 dogs necropsied 10 days after oral inoculation with 100,000 C. canis oocysts; both dogs had excreted oocysts 9 days PI. Asexual and sexual stages were seen in the lamina propria, throughout the small intestine. Merozoites of different sizes were present, often in the same vacuole. They were arranged singly, in pairs, and many within a single parasitophorous vacuole. The maximum number of nuclei within developing merozoites in a group was 8, but it could not be discerned if they were individual nuclei or parts of merozoites. Findings of asexual stages 1 day after dogs had started excreting oocysts indicated continued asexual multiplication beyond the prepatent period. The stages found resemble the 3 generations reported previously. The mode of division of the asexual generations remains unclear. The results of the present study indicate that there are many generations, that are difficult to determine because of the multiplication of merozoites in the original host cell without leaving it to enter new host cells. From the literature, it is evident that cat and dog coccidia (Cystoisospora spp.) divide by more than 1 type of division, including endodyogeny. In the past, the schizont/meront groups containing more than 1 generation have been called “cysts”. However, cyst is not a good term because cyst is a term best used for an orally infective stage of coccidia and monozoic tissue cysts of C. canis can occur in paratentic hosts and it has been used for encysted stages in extra intestinal organs. We prefer the term “types” as originally proposed for intestinal stages of Toxoplasma gondii. Ultrastructural studies are needed to resolve mode of multiplication of canine Cystoisospora species.