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.

Support for targeted sampling of red fox (Vulpes vulpes) feces in Sweden: a method to improve the probability of finding Echinococcus multilocularis

“…Fox feces were collected during 2013–2015 as part of a research project investigating E. multilocularis in rodents in Sweden [5]. Collections occurred within four study regions within the municipalities of Katrineholm, Uddevalla, Gnesta/Nyköping, and Vetlanda/Växjö (Fig.…”

“…All study regions were located in the south of Sweden because the fox density was estimated to be higher in the south than in the north and because no positives had been found north of Borlänge (60.48°N, 15.43°E) [4]. For a more detailed description of field design and rodent trapping methods see Miller et al [5]. …”

“…The targeted rodent species were water voles, field voles and bank voles ( Myodes glareolus ). These are species with a wide geographical range in Sweden and which are closely related to species reported to have a high prevalence of E. multilocularis in central Europe [5, 17, 18]. Rodent trapping sites were selected based on the following criteria: expert knowledge of preferred habitat for the targeted rodent species, presence of rodent activity (i.e.…”

“…In Sweden, the red fox is considered the major definitive host [3], and early results indicate that rodent intermediate hosts include both the field vole ( Microtus agrestis ) and the water vole ( Arvicola amphibius ) [5]. Foci of high numbers of infected foxes are reported in many countries, including Germany [6] and France [7].…”

“…As the rodent intermediate host(s) was yet unknown, the primary purpose was to identify the rodent host and to describe characteristics of the parasite infection within these hosts in Sweden [5]. Because parasite prevalence in foxes was estimated to be extremely low (0.1%), sampling was designed to maximize the likelihood of finding the parasite and considered the optimal conditions for transmission outlined above [13].…”