Eggs as a Suitable Tool for Species Diagnosis of Causative Agents of Human Diphyllobothriosis (Cestoda).

Kateřina Leštinová,Tomáš Scholz,Miroslava Soldánová,Roman Kuchta,Ricardo Toshio Fujiwara

doi:10.1371/journal.pntd.0004721

Abstract

BackgroundTapeworms of the order Diphyllobothriidea are parasites of tetrapods and several species may infect man and cause neglected human disease called diphyllobothriosis. Identification of human-infecting diphyllobothriid cestodes is difficult because of their morphological uniformity, which concerns also their eggs in stool samples.MethodsIn the present study, we analysed by far the largest dataset of more than 2,000 eggs of 8 species of diphyllobothriid cestodes that may infect humans, including the most frequent human parasites Diphyllobothrium latum, D. nihonkaiense and Adenocephalus pacificus (syn. Diphyllobothrium pacificum). Size (length, width and length/width ratio) and the surface of the egg shell from naturally and experimentally infected hosts were studied using light and scanning electron microscopy.ResultsA high degree of intraspecific and host-related size variability has been detected, but combination of morphometrical and ultrastructural data made it possible to distinguish all of the studied species, including otherwise quite similar eggs of the 3 most common species infecting man, i.e. D. latum, D. nihonkaiense and D. dendriticum. The surface of all marine species is covered by numerous deep pits with species-specific density, whereas the surface of freshwater species is smooth or with isolated shallow hollows or wrinkles.

Highlights

Human infections with gastrointestinal helminths are usually diagnosed when their eggs are found in stool samples
We analysed by far the largest dataset of more than 2,000 eggs of 8 species of diphyllobothriid cestodes that may infect humans, including the most frequent human parasites Diphyllobothrium latum, D. nihonkaiense and Adenocephalus pacificus
A high degree of intraspecific and host-related size variability has been detected, but combination of morphometrical and ultrastructural data made it possible to distinguish all of the studied species, including otherwise quite similar eggs of the 3 most common species infecting man, i.e. D. latum, D. nihonkaiense and D. dendriticum

Summary

Introduction

Human infections with gastrointestinal helminths are usually diagnosed when their eggs are found in stool samples. Eggs of diphyllobothriid tapeworms including human-infecting species are highly variable, their size may overlap between species and is influenced by individual definitive hosts and their size This makes reliable species diagnosis of causative agents of human diphyllobothriosis in stool samples difficult or even impossible [2]. Out of 16 species of diphyllobothriids reported from man, only the following 4 are common parasites of man, namely Diphyllobothrium latum (Linnaeus, 1758) with circumboreal distribution (with few cases reported from Chile), D. nihonkaiense Yamane, Kamo, Bylund and Wikgren, 1986 in the northern Pacific region, Adenocephalus pacificus Nybelin, 1931 endemic in the southern Pacific, and Diphyllobothrium dendriticum (Nitzsch, 1824) with arctic distribution [2,3,4] These cestodes, commonly called broad or fish tapeworms, produce up to 36,000 eggs per day [6,7]. Identification of human-infecting diphyllobothriid cestodes is difficult because of their morphological uniformity, which concerns their eggs in stool samples

Methods

Results

Conclusion