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 host s (foxes, dogs, cats etc.). In this indication the intestinal scraping tech nique (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 ca n be regarded as "gold standard". Both IST and SCT are highly specific as p arasite identification is based on distinct morphological criteria. Detecti on of serum antibodies using highly specific tests is not suitable for esti mating the actual prevalence of E. multilocularis in definitive hosts becau se of insufficient correlation between the prevalence of serum antibodies a nd 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 o f intestinal immature and mature parasite stages and their numbers. In vari ous laboratories different types of CA-ELISA's exhibited sensitivities betw een 84 and 95% and very high specificities (> 95%), the latter with regard to non-Echinococcus cestodes (Taenia spp., Mesocestoides spp. etc.) and nem atodes. Cross reactivity with E. granulosus may occur in these tests. DNA-d etection in faecal material by PCR is also highly specific (100%) and sensi tive (89-100%) (at least 84%) in diagnosing intestinal E. multilocularis bu rdens. The CA-ELISA is now established in several laboratories, and commerc ial test kits are available. It is likely that this test can replace the IS T in large epidemiological surveys in the near future. We recommend this te st for primary screening, and PCR as secondary confirmation test. The perfo rmance characteristics of the various methods are compared and discussed. R ecent studies have shown that coproantigen prevalence (determined by a CA-E LISA) in fox faeces collected in the field can reflect medium and high prev alences of E. multilocularis in fox populations. Metacestodes in intermedia te and aberrant host animals can be diagnosed at necropsy at post mortem ex amination by identification of typical macroscopic and histological parasit e structures. In case of doubt, especially when small lesions are present, E. multilocularis can be diagnosed or excluded by applying an immunofluores cent monoclonal antibody (G11) to squash preparations or by DNA-detection ( PCR).