High prevalence of Echinococcus multilocularis in urban red foxes (Vulpes vulpes) and voles (Arvicola terrestris) in the city of Zürich, Switzerland

S. HOFER a1, S. GLOOR a2a3, U. MÜLLER a4, A. MATHIS a1, D. HEGGLIN a1a2 and P. DEPLAZES a1c1
a1 Institute of Parasitology, University of Zürich, Winterthurerstrasse 266a, 8057 Zürich, Switzerland
a2 Work Group Urban Ecology and Wildlife Research, Wuhrstrasse 12, 8003 Zürich, Switzerland
a3 Zoological Museum, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
a4 Swiss Rabies Centre, University of Bern, Länggassstrasse 122, 3012 Berne, Switzerland


Over a period of 26 months from January 1996 to February 1998, 388 foxes from the city of Zürich, Switzerland, were examined for intestinal infections with Echinococcus multilocularis and other helminths. The prevalence of E. multilocularis in foxes sampled during winter increased significantly from 47% in the urban to 67% in the adjacent recreational area, whereas prevalence rates of other helminths were similar in both areas. Seasonal differences in the prevalence of E. multilocularis were only found in urban subadult male foxes which were significantly less frequently infected in summer than in winter. The distribution of the Echinococcus biomass, as expressed by worm numbers per fox was overdispersed in 133 infected foxes randomly sampled in winter. Ten of these foxes (8%) were infected with more than 10000 specimens and carried 72% of the total biomass of E. multilocularis (398653 worms). Prevalences did not differ significantly in these foxes in regard to age and sex but worm burdens were significantly higher in subadult foxes as compared with adult foxes. In voles (Arvicola terrestris) trapped in a city park of Zürich, E. multilocularis metacestodes were identified by morphological examination and by PCR. The prevalence was 20% among 60 rodents in 1997 and 9% among 75 rodents in 1998. Protoscoleces occurred in 2 of the cases from 1997. The possible risk for human infection is discussed with respect to the established urban E. multilocularis cycle.

(Received June 13 1999)
(Revised August 31 1999)
(Accepted September 2 1999)

Key Words: Echinococcosis; Echinococcus multilocularis; Arvicola terrestris; Vulpes vulpes; urban; zoonosis.

c1 Corresponding author: Institute of Parasitology, University of Zürich, Winterthurerstrasse 266a, CH-8057 Zürich, Switzerland. Tel: +41 1 6358510. Fax: +41 1 6358907. E-mail: