Spurious passage of Calodium hepaticum in human stools misidentified as Trichuris spp. infection in school-age children in Angola

ABSTRACT Calodium hepaticum (syn. Capillaria hepatica ) is a zoonotic parasite of murid rodents and other mammals, while also being an important agent of hepatic capillariasis in humans. In a cross-sectional survey of schoolchildren across three provinces (Huambo, Uíge, and Zaire) in Angola, we found 39 fecal specimens that were considered positive for Trichuris trichiura eggs using the Kato-Katz thick smear but were negative by quantitative polymerase chain reaction (qPCR). Further morphological examination of these putative Trichuris eggs identified them as having an asymmetrical bipolar plug morphology, resembling capillariid eggs. Molecular characterization through Sanger sequencing and nanopore metabarcoding confirmed these eggs as C. hepaticum , indicating spurious human passage. Once passed in human feces, these eggs may embryonate and become infective in the environment, with the potential to cause hepatic capillariasis in humans. Future research should assess the prevalence of both spurious passage and hepatic capillariasis in humans in Angola, as well as evaluate the impact of misidentification of these nematodes with Trichuris eggs on soil-transmitted helminths surveys. IMPORTANCE Calodium hepaticum causes hepatic capillariasis in humans living in low- to upper-middle income countries. This disease is mainly caused by ingestion of embryonated eggs, whereas consumption of eggs that are unembryonated, such as those found in the livers of infected animals, leads to spurious passage. Notably, unembryonated eggs are morphologically similar to those of T. trichiura , leading to potential misdiagnosis in routine fecal examinations and inaccurate estimates of soil-transmitted helminth prevalence. In this study, we detected C. hepaticum eggs in fecal specimens initially identified as positive for T. trichiura eggs by the Kato-Katz thick smear but tested negative by qPCR. Our findings highlight diagnostic challenges posed by such morphological similarities. Additionally, the detection of C. hepaticum eggs in fecal specimens from school-aged children suggests a potential risk of hepatic capillariasis in this population, underscoring the importance for local health authorities and medical practitioners in Angola to consider this parasite as a potential differential diagnosis in cases of unexplained hepatic dysfunction.