Studies on Sylvatic Echinococcosis

Abstract

From three different habitats in North Dakota 5,638 deer mice, Peromyscus maniculatus, were examined for larval Echinococcus multilocularis infections during 1965 through 1972. Infection was found in 224 (4%) of these mice. Yearly differences in prevalence were evident, with a low of 1.1% during 1971 and a high of 7.8% in 1968. These yearly differences were partially attributable to host density, habitat sampled, and climatic season during which the mice were taken. Since the year was not a legitimate variable, the total over-years data were used to assess the relative influence of sex and age of the host, habitat, and climatic season on the prevalence of the larval parasite. The rate of infection varied significantly with habitat. Seasonally, the highest prevalence was observed during spring (6.5%), followed by summer (5.5%), autumn (2.2%), and winter (2.0%). The prevalence in adult mice was over 10 times greater than in juveniles (4.5% vs. 0.4%), while more males were infected than females (4.6% vs. 3.1%). A factorial analysis of variance showed the order of importance of these variables to be 1) age, 2) habitat, 3) season, 4) age by season, 5) age by habitat, and 6) habitat by season. A mathematical model based on the functions of these variables and accounting for about 74% of the variation is suggested for the prediction of prevalences of larval E. multilocularis in this intermediate host.