Practical guide for the diagnosis of helminth ova in stools

Abstract

In the age of globalization of infectious diseases, qualified personnel is needed for thediagnosis of parasitic diseases in the laboratory. This review aimed to introduce the methodsfor stool examination and identification of helminth eggs for the diagnosis of helminthicinfections in laboratory and field surveys. The formalin-ether sedimentation technique (FEST)and the Kato-Katz egg counting technique (KKECT) are mainly described as representativestool examinations. The FEST is somewhat complicated and troublesome, but it is useful fordifferentiating small trematode eggs from opisthorchiid and heterophyid flukes. KKECT isuseful in field surveys of large populations in areas endemic for soil-transmitted helminthiases. Helminth eggs are divided into four groups based on the presence or absence of theoperculum and embryo. The eggs of Clonorchis sinensis and heterophyid flukes includingMetagonimus spp. are relatively small and contain an operculum and an embryo (miracidium). Meanwhile, eggs of diphyllobothriid tapeworms, echinostomatid flukes, Paragonimuswestermani, Fasciola hepatica, and Fasciolopsis buski are relatively larger, operculated, andcontain germ cells and yolks instead of the embryo. The eggs of cyclophyllidian tapeworms,Taenia spp. and Hymenolepis spp., and blood flukes, Schistosoma spp., are embryonatedbut do not have an operculum. Nematode eggs have no operculum and embryo, but thoseof hookworms and pinworms sometimes have developed larvae inside. This review providesvaluable insights into the methods of stool examination and helminth egg identification forthe diagnosis of helminthic infections in the laboratory and field surveys.