Endogenous development of Cystoisospora belli in intestinal and biliary epithelium of humans

Authors: Dubey, Jitender; EVASON, KIMBERLY - University Of Utah; WALTHER, ZENTA - Yale University

Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2019
Publication Date: 3/1/2019
Citation: Dubey, J.P., Evason, K., Walther, Z. 2019. Endogenous development of Cystoisospora belli in intestinal and biliary epithelium of humans. Parasitology. 146:865-872. https://doi.org/10.1017/S003118201900012X.
DOI: https://doi.org/10.1017/S003118201900012X

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 belli is a pathogenic coccidian of humans. Its life cycle is not fully known. Here, the authors describes asexual cycle (meronts,schizonts) and sexual cycle of C. belli in biopsy specimens of small intestine of one and the common bile duct of another patient. Despite numerous studies mentioning the presence of asexual and sexual stages of C. belli in human intestinal and biliary epithelium over the last 50 years no study had successfully described the structural features and modes of development of C. belli in humans. The present study achieved that goal using known features of development of intestinal stages of Cystoisospora species from dogs, cats, and pigs and enteroepithelial stages of T. gondii in cats as a foundation to provide a narrative of the endogenous development of C. belli. This will provide a useful tool for pathologists and others interested in infectious diseases.

Technical Abstract: Cystoisospora (Isospora) belli is a coccidian parasite of humans. It can cause serious digestive disorders involving infection of intestines, biliary tract and gallbladder, especially in those with depressed immunity. It has a direct fecal-oral transmission cycle. After ingestion of sporulated oocysts, the parasite multiplies asexually and sexually within host epithelial cells, resulting in unsporulated oocysts that are excreted in feces. The details of asexual and sexual stages are not known and certain inclusions in epithelial cells in biopsy samples have been erroneously identified recently as C. belli. Here, we provide details of developmental stages of C. belli in two patients, in duodenal biopsy of one and biliary epithelium of the other. Immature and mature asexual stages (schizonts/ meronts) were seen in epithelial cells. The merozoites were seen singly, in pairs, and in groups in single parasitophorous vacuole (pv) in host cytoplasm. Immature and mature meronts were seen together in the same pv; up to 8 nuclei were seen in meronts that retained elongated crescent shape; round multinucleated schizonts, seen in other coccidians, were not found. Meronts were up to 25 µm long and contained up to 10 merozoites that were 8-11 µm long. The merozoites and meronts contained PAS-positive granules. Microgamonts (male) contained up to 30 nuclei that were arranged at the periphery and had condensed chromatin; 1-3 PAS-positive, eosinophilic, residual bodies were left when microgametes were formed. The microgametes were 4 µm long and PAS-negative. All stages of macrogamonts, including oocysts were PAS-positive. The detailed description of the life cycle stages of C. belli reported here should facilitate in histopathologic diagnosis of this parasite.