Practical guide for the diagnosis of helminth ova in stools

Abstract

In the age of globalization of infectious diseases, qualified personnel is needed for the diagnosis of parasitic diseases in the laboratory. This review aimed to introduce the methods for stool examination and identification of helminth eggs for the diagnosis of helminthic infections in laboratory and field surveys. The formalin-ether sedimentation technique (FEST) and the Kato-Katz egg counting technique (KKECT) are mainly described as representative stool examinations. The FEST is somewhat complicated and troublesome, but it is useful for differentiating small trematode eggs from opisthorchiid and heterophyid flukes. KKECT is useful 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 the operculum and embryo. The eggs of Clonorchis sinensis and heterophyid flukes including Metagonimus spp. are relatively small and contain an operculum and an embryo (miracidium). Meanwhile, eggs of diphyllobothriid tapeworms, echinostomatid flukes, Paragonimus westermani, Fasciola hepatica, and Fasciolopsis buski are relatively larger, operculated, and contain germ cells and yolks instead of the embryo. The eggs of cyclophyllidian tapeworms, Taenia spp. and Hymenolepis spp., and blood flukes, Schistosoma spp., are embryonated but do not have an operculum. Nematode eggs have no operculum and embryo, but those of hookworms and pinworms sometimes have developed larvae inside. This review provides valuable insights into the methods of stool examination and helminth egg identification for the diagnosis of helminthic infections in the laboratory and field surveys.

Keywords

• stool examination
• formalin-ether sedimentation technique
• kato-katz egg counting technique
• helminth eggs
• identification key