Echinococcus multilocularis in the cotton rat. The effect of preexisting subcutaneous cysts on the development of a subsequent intraperitoneal inoculum of protoscolices.

Cotton rats were inoculated subcutaneousiy with small cysts of Echinococcus multilocularis and challenged intraperitoneally with 100 protoscolices 40 days later. Subcutaneous cysts which attained weights of more than about 5 g effectively suppressed the establishment, growth, and transperitoneal dissemination of the challenging infection. Normal cotton rats, inoculated intraperitoneally with 100 protoscolices, characteristically developed massive cysts which weighed, on the average, 31 g and consisted of about 31 cyst clusters. In contrast, animals which already harbored large, subcutaneous cysts developed only very mild infections following intraperitoneal reinoculation. Such hosts supported never more than two small, intraperitoneal cysts with a mean total weight of less than 1 g. The intensity of this suppression was underscored by the fact that even a single protoscolex or a small vesicle of E. multilocularis inoculated intraperitoneally into normal cotton rats could give rise to 11 g of cyst material...