International multicentre study to validate the Segmental Sedimentation and Counting Technique (SSCT) for the surveillance of Echinococcus multilocularis in red fox.

The fox tapeworm, Echinococcus multilocularis, is the etiological agent of the severe zoonotic disease alveolar echinococcosis. The Sedimentation and Counting Technique (SCT) has long been considered the gold standard for detecting these worms in the intestines of dead foxes. Several alternative methods, including the Segmental Sedimentation and Counting Technique (SSCT), have been developed, aiming to reduce time of analysis while maintaining high sensitivity. In this study, the performance of the SSCT was first evaluated by comparison with the SCT in the context of E. multilocularis surveillance in three countries and, secondly, a proficiency test scheme was organized to assess the capability of national reference laboratories for parasites in 14 European countries to perform the SSCT. The analysis of 375 small intestines of positive red foxes (Vulpes vulpes) divided in four equal segments showed that combining the second (S2) and fourth (S4) segments achieved the highest sensitivity (99.2 %). Moreover, the same segment combination reached 100 % sensitivity among 11 infected raccoon dogs. The SSCT based on the analysis of the segments pair S4/S2 can therefore be recommended for the diagnosis of E. multilocularis infection in red foxes. For raccoon dogs (Nyctereutes procyonoides), the S4/S2 segments pair analysis also seems highly promising, though additional data are needed. Results from this proficiency test confirm the easy implementation of the method, even in laboratories without routine experience in scraping methods. Overall, this study demonstrates that the SSCT can be considered a simple, rapid, and highly sensitive reference method for post mortem diagnosis of E. multilocularis infection in red foxes, including for large-scale surveillance programs.