Immunological and molecular techniques for diagnosing the Echinococcus multilocularis infection in definitive and intermediate hosts

Until recently parasite detection at necropsy was the only reliable method for diagnosing the Echinococcus multilocularis infection in definitive hosts (foxes, dogs, cats etc.). In this indication the intestinal scraping technique (IST) was predominantly used in large surveys of fox populations. The IST has a sensitivity of 78% as compared to the sedimentation and counting technique (SCT) which is more precise (sensitivity similar to 100%) and can be regarded as "gold standard". Both IST and SCT are highly specific as parasite identification is based on distinct morphological criteria. Detection of serum antibodies using highly specific tests is not suitable for estimating the actual prevalence of E. multilocularis in definitive hosts because of insufficient correlation between the prevalence of serum antibodies and of intestinal worm burdens. The coproantigen-ELISA (CA-ELISA) can detect E. multilocularis antigens in faecal material already during the prepatent period, and coproantigen excretion is closely correlated to the presence of intestinal immature and mature parasite stages and their numbers. In various laboratories different types of CA-ELISA's exhibited sensitivities between 84 and 95% and very high specificities (> 95%), the latter with regard to non-Echinococcus cestodes (Taenia spp., Mesocestoides spp. etc.) and nematodes. Cross reactivity with E. granulosus may occur in these tests. DNA-detection in faecal material by PCR is also highly specific (100%) and sensitive (89-100%) (at least 84%) in diagnosing intestinal E. multilocularis burdens. The CA-ELISA is now established in several laboratories, and commercial test kits are available. It is likely that this test can replace the IST in large epidemiological surveys in the near future. We recommend this test for primary screening, and PCR as secondary confirmation test. The performance characteristics of the various methods are compared and discussed. Recent studies have shown that coproantigen prevalence (determined by a CA-ELISA) in fox faeces collected in the field can reflect medium and high prevalences of E. multilocularis in fox populations. Metacestodes in intermediate and aberrant host animals can be diagnosed at necropsy at post mortem examination by identification of typical macroscopic and histological parasite structures. In case of doubt, especially when small lesions are present, E. multilocularis can be diagnosed or excluded by applying an immunofluorescent monoclonal antibody (G11) to squash preparations or by DNA-detection (PCR).