First Report of Choleoeimeria sp. (Apicomplexa: Eimeriidae) from the Burton's Carpet Viper Echis pyramidum (Reptilia: Viperidae) in Egypt with a Taxonomic Revision on Choleoeimeria spp. from Vipers of the World.

BACKGROUND: The genus Choleoeimeria was established in 1989 to accommodate tetrasporocystic, dizoic coccidians characterized by ellipsoidal oocysts with a shape index exceeding 1.4 that specifically parasitize the biliary epithelium of various reptilian hosts.The current study provides the first record of Choleoeimeria sp. (Apicomplexa: Eimeriidae) from the gall bladder and intestinal contents of Burton's carpet viper, Echis pyramidum (Reptilia: Viperidae), collected from the Bahariya Oases in the Western Desert of Egypt. METHOD: Ten specimens of the viper Echis pyramidum were collected from the Western Desert of Egypt and subjected to parasitological screening via direct microscopic examination of fecal suspensions and bile fluid to identify coccidian oocysts. Heavily infected individuals were humanely euthanized with isoflurane to facilitate morphometric analysis of the oocysts and sporocysts. Subsequently, internal organs—including the gall bladder, liver, and intestines—were fixed in Bouin’s solution and processed for histological examination using hematoxylin and eosin (H&E) staining to characterize the endogenous developmental stages. RESULTS: Sporulated oocysts measured 35.9–42.9 × 21.3–24.0 µm (40.9 ± 2.5 × 22.7 ± 1.0 µm) with length/width ratio of 1.6–2.0 (1.8 ± 0.1). Micropyle, polar granules, and oocyst residuum were absent. Oocyst wall was smooth, bilayered,and measured 1.0–1.4 µm (1.2 ± 0.2 µm). Sporocysts were subspherical to slightly ellipsoidal with a bivalve single-layered wall, measuring 11.3–12.2 × 9.5–10.3 µm (11.8 ± 0.3 × 9.8 ± 0.3 µm). Endogenous stages were observed withinthe apical cytoplasm of epithelial cells lining the gall bladder and bile ducts.Mature meronts measured 16.8–20.8 × 15.7–18.6 µm (18.6 ± 2.0 × 17.2 ± 1.3 µm) and contained up to 16 crescent-shaped merozoites, while mature macrogamont were round, measured 22.4–24.6 × 22.0–23.9 µm (23.2 ± 1.2 × 22.9 ± 0.8 µm), and developed distinct wall-formingbodies. CONCLUSION: This study provide a new perspective for studying the pathogenic mechanisms of T. gondii, revealing that GRA72 modulThe present study documents the first record of Choleoeimeria sp. infecting Echis pyramidum in Egypt and proposes the formal description of a new species, Choleoeimeria echisi. The research provides a comprehensive morphological and morphometric characterization of both exogenous and endogenous stages localized within the gall bladder and intestinal tract. These findings contribute significantly to the taxonomic revision of the genus Choleoeimeria and establish a critical baseline for assessing the pathogenicity and ecological implications of coccidian infections in reptilian hosts. Keywords:Choleoeimeria, Viperidae, Apicomplexa, oocysts, gall bladder