Endogenous developmental cycle of the human coccidian, Cyclospora cayetanensis

Authors: Dubey, Jitender; ALMERIA, S - Food And Drug Administration(FDA); Mowery, Joseph; FORTES, J - Autonomous University Of Madrid

Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2020
Publication Date: 4/21/2020
Citation: Dubey, J.P., Almeria, S., Mowery, J.D., Fortes, J. 2020. Endogenous developmental cycle of the human coccidian, Cyclospora cayetanensis. Parasitology. 106(2):295-307. https://doi.org/10.1645/20-21.
DOI: https://doi.org/10.1645/20-21

Interpretive Summary: Cyclospora cayetanensis is a coccidian parasite of humans of known and growing importance. However, we are surprisingly naïve as to our understanding of how to diagnose it and how it develops inside the human body. The life cycle of C. cayetanensis has not been fully described. The oocyst is the only stage definitively identified. After the ingestion of sporulated oocysts in contaminated food, water, or soil by a host, sporozoites are thought to excyst in the gut lumen and invade the enterocytes of the epithelium of small intestine, where the sporozoites round up and subsequently form asexual and sexual stages. Unsporulated oocysts are excreted in feces. Previous information on the life cycle stages is derived from piece meal information by examination of biopsy samples from patients with gastrointestinal disorders. There is considerable confusion concerning the stages found, terminology used, and misidentification of stages. Here, the authors provide first detailed description of the parasite in sections of gallbladder of a HIV patient in 2011. Detailed observations reported here using light microscopy, transmission electron microscopy and molecular techniques should help pathologists to diagnose C. cayetanensis infections.

Technical Abstract: Cyclospora cayetanensis is a coccidian parasite of humans of known and growing importance. However, we are surprisingly naïve as to our understanding of how to diagnose it and how it develops inside the human body. Here, we provide details of developmental stages of C. cayetanensis in gallbladder of a 33-year old male HIV-patient. The gallbladder had been removed surgically in 2001 because of severe abdominal pain. For the present study, the archived paraffin block of gallbladder was processed for light microscopic and transmission electron microscopy (TEM). Histological sections were examined after staining with haematoxylin and eosin or periodic acid Schiff reaction. Immature and mature asexual stages, gamonts, and oocysts were seen in epithelial cells, both in superficial epithelium and in glands. The merozoites were present singly, in pairs and 3 or more in single parasitophorous vacuole (pv) in the host cytoplasm. Up to 6 nuclei were seen in immature schizonts without evidence of merozoite formation. Mature schizonts were 7.6 x 5.1 µm and contained up to ten 3-4 µm long merozoites. Merozoites were 0.6 to 2.0 µm wide and their shape varied from pear shaped to slender. Merozoites were PAS-positive; however, some were intensely positive, some had only minute granules, while others were PAS-negative. The micro (male) gamonts were 6.6 x 5.2 µm and contained less than 20 microgametes around a residual body. The microgametes were up to 2-µm long. Macro (female) gamonts contained distinctive eosinophilic wall forming bodies (WFB) that varied in size, and were less than 1µm in HE-stained sections. Macrogamonts were: 5.8-6.5 x 5.3-6.5 µm. Oocysts in sections were unsporulated and had a diameter of 5.7-7.5 µm. TEM examination confirmed the histologic findings. The DNA extracted from paraffin sections was confirmed as C. cayetanensis by real time PCR. The detailed description of the life cycle stages of C. cayetanensis reported here should facilitate histopathologic diagnosis of this parasite. We have shown that the parasite’s development more closely resembles that of Cystoisospora than Eimeria, have shown multiple nuclei per immature meront indicating schizogony, and have undermined evidence for a Type II meront.