Loss of tegumental papillae and spines during maturation of Clonorchis sinensis: Evidence from colchicine disruption.

Clonorchis sinensis is a foodborne liver fluke and Group 1 carcinogen endemic to East Asia. Its syncytial tegument mediates host-parasite interactions and serves as the primary target of praziquantel (PZQ), which exhibits reduced efficacy against juvenile stages. This study investigated whether tegumental papillae and spines are truly lost or internalized during the maturation of C. sinensis, and employed colchicine as a diagnostic perturbation to probe for subtegumental remnants. Excysted metacercariae, juvenile worms (10 days postinfection), and adult worms (4 weeks postinfection) were examined using scanning electron microscopy; a subset of adults was treated with colchicine (1 µM, 37°C, 6 h). Tegumental spines were quantified per 100 µm² on calibrated images. Spine density declined from 36 ± 2 / 100 µm² in metacercariae to 6 ± 1 / 100 µm² in juveniles (Welch's t-test, P < 0.05) and was below quantifiable limits in adults (0-2 / 100 µm², qualitative). Colchicine-treated adults exhibited distal surface fragmentation without revealing hidden spines or papillae. These findings provide quantitative morphological evidence that papillae and spines are progressively lost, rather than internalized, during maturation of C. sinensis, thereby clarifying a key aspect of tegumental remodeling across developmental stages.