Establishment and application of the laboratory colony of Clethrionomys rufocanus bedfordiae susceptible to Echinococcus multilocularis for the antagonistic competion among taeniid species

Echinococcosis, also known as hydatid disease, is one of the most important cestode of man, domestic and wild animals. It is widely distributed in the world and recent information points to a spread of the disease into area previously free. In japan alveolar hydatid disease, caused by Echinococcus multilocularis, has further been reported in many hitherto Znon-endemicZ areas in Hokkaido in the past year, bringing the total number of endemic administrative districts to 121 in Hokkaido out of 212 in April 1988. The final goal of this project is the biological control of this parasite by the application of antagonistic competition between E. multilocularis and a closely related cestode in the laboratory-reared Clethrionomys rufocanus badfordiae. Four strains of E. multilocularis and 4 species with 8 strains of taeniid cestodes, i. e., Taenia taeniaeformis, T. crassiceps, T. polyacantha and T. hydatigena, have been isolated and maintained by serial passage in laboratory animals for this purpose. The laoboratory colony of C. rufocanus bedfordiae has been established under the conditions of a temperature of 22 2゜c, a humidity of 55 5%, a ventilation of 10-15 times/hour with fresh air and 14 hours of lighting. The results showed that the gestation period was 18-22 days, the pregnancy rate was ca. 35%, the litter size averaged 5.1 1.6 and the weaning rate was 70-90%. The polymorphism of mitochondrial DNA among the populations and their serum isotypic immuno- globulines were caracterized. Antagonistic competion between closely related taeniid cestodes has been observed first by using the rat system, i. e., the strain of T. taeniaeformis -C. rufocanus origin which is resistant to rat can suppress completely the challenged infection of the rat susceptible strain in Wistar rats. Then, it has been confirmed that the number of established cycts of E. nultilocularis in the liver of C. rufocanus previously infected with C. rufocanus strain of T. taeniaeforis and of E. multilocularis alone show significant difference, i. e,. 16.9 4.4 and 35.0 15.0(p<0.05) for 2 weeks interval and 25.7 11.1 and 46.0 17.7(p<0.01) for 3 weeks interval of challenged infection, respectively.