title: First identification of Echinococcus multilocularis in rodent intermediate hosts in Sweden.
abstract: Echinococcus multilocularis is a zoonotic tapeworm with a sylvatic lifecycle and an expanding range in Europe. Monitoring efforts following its first identification in 2011 in Sweden have focused on the parasite's definitive host, the red fox (Vulpes vulpes). However, identifying rodent intermediate hosts is important to recognize opportunities for parasite transmission. During 2013-2015, livers from a total of 1566 rodents from four regions in Sweden were examined for E. multilocularis metacestode lesions. Species identity of suspect parasite lesions was confirmed by PCR and sequencing. E. multilocularis positive lesions >6 mm in diameter were also examined histologically. One Microtus agrestis out of 187 (0.5%, 95%CI: 0-2.9%), 8/439 (1.8%, 95%CI: 0.8-3.6%) Arvicola amphibius, 0/655 (0%, 95%CI: 0-0.6%) Myodes glareolus, and 0/285 (0%, 95%CI: 0-1.3%) Apodemus spp. contained E. multilocularis metacestode lesions. Presence of protoscoleces was confirmed in the infected M. agrestis and in three of eight infected A. amphibius. Six of the nine positive rodents were captured from the same field. This is the first report of E. multilocularis in intermediate hosts in Sweden. The cluster of positive rodents in one field shows that local parasite prevalence can be high in Sweden despite overall low national prevalence in foxes (<0.1%). The presence of protoscoleces in infected M. agrestis and A. amphibius indicate these species can serve as competent intermediate hosts in Sweden. However, their relative importance for E. multilocularis transmission in the Swedish environment is not yet possible to assess. In contrast, the negative findings in all M. glareolus and Apodemus spp. suggest that these species are of no importance.
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Section for Parasitology, Swedish University of Agricultural Sciences, Box 7036, Uppsala, 750 07, Sweden.
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Miller
authors.affiliation: Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, 901 83, Sweden.
authors.forename: Gert E
authors.initials: GE
authors.lastname: Olsson
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Section for Parasitology, Swedish University of Agricultural Sciences, Box 7036, Uppsala, 750 07, Sweden.
authors.forename: Marion R
authors.initials: MR
authors.lastname: Walburg
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Section for Parasitology, Swedish University of Agricultural Sciences, Box 7036, Uppsala, 750 07, Sweden.
authors.forename: Sofia
authors.initials: S
authors.lastname: Sollenberg
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Section for Parasitology, Swedish University of Agricultural Sciences, Box 7036, Uppsala, 750 07, Sweden.
authors.forename: Moa
authors.initials: M
authors.lastname: Skarin
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Section for Pathology, Swedish University of Agricultural Sciences, Box 7028, Uppsala, 750 07, Sweden.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Ley
authors.affiliation: Department of Disease Control and Epidemiology, Zoonosiscenter, National Veterinary Institute, Uppsala, 751 89, Sweden.
authors.forename: Helene
authors.initials: H
authors.lastname: Wahlström
authors.affiliation: Department of Biomedical Sciences and Veterinary Public Health, Section for Parasitology, Swedish University of Agricultural Sciences, Box 7036, Uppsala, 750 07, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Höglund
keywords: Arvicola amphibius; Echinococcus multilocularis; Intermediate host; Microtus agrestis; Rodent; Sweden