Echinococcus multilocularis in wild boar : aiming at an alternative surveillance method

Abstract: This study was the first part of a larger project investigating a new surveillance method for Echinococcus multilocularis. In this study we examined livers from wild boar (Sus scrofa), looking for lesions caused by E. multilocularis. E. multilocularis is a small tapeworm which has an indirect life cycle. The definitive host is usually the red fox (Vulpes vulpes) and intermediate hosts are rodents, for example the European water vole (Arvicola terrestris). But E. multilocularis can use many other species of carnivores as definitive hosts and other rodents as intermediate hosts. In the definitive host the parasite is found in the intestine as the adult worm. Proglottids are shed by the definitive host and ingested by the intermediate host in which cysts develop in the liver. This disease is called alveolar echinococcosis. Other animals, including humans that are not considered normal intermediate hosts can also develop alveolar echinococcosis. These animals are referred to as accidental hosts because they are unlikely to become part of the lifecycle. This is either because the parasite does not develop fully in these animals or that these animals are unlikely to become prey to a definitive host. Examples of accidental hosts are wild boar and pig (Sus scrofa) and horse (Equus ferus caballus). The lesions found in pigs are similar to those in the intermediate hosts, but the metacestode is not fully developed. The disease in humans has a very long incubation time, varying from five to fifteen years. The case fatality rate is high but the incidence is low with approximately 18’000 new cases per year worldwide. Surveillance methods have traditionally been based on identifying infection in the definitive host. The method mostly used in Sweden is the sedimentation and counting technique (SCT), often combined with copro-enzyme-linked immunosorbent assay (ELISA). These methods have high sensitivity and specificity but are expensive, time consuming and pose a risk of infection to persons performing it. For this study, 80 livers from Swedish wild boars were collected and examined macro- and microscopically. Four livers had lesions that looked like “white spots”, probably caused by migrating Ascaris suum. These lesions were tested with PCR and no E. multilocularis DNA was detected. No E. multilocularis lesions were found. It was concluded that the samples in this study could be used as a negative reference material in the continued project which in turn would investigate whether it would be possible to use the detection of antibodies to E. multilocularis in wild boar, using ELISA, and whether this could be used as a surveillance method.