A Natural Population of Anomalous Branched Tapeworms, Hymenolepis nana (Cestoda : Hymenolepididae), in a Colony of DBA/1 Mice

Abstract

DURING work on metabolism of the dwarf tapeworm of mice (Hymenolepis nana), a natural infection with this parasite was found in a local colony of DBA/1 mice (Curd's Caviary, Downey, California). Of 500 mice from this colony examined over a two-year period, 320 were infected with an average of 35 worms per mouse, varying from a single 12-in. worm to one or two thousand extremely small ones (demonstrating a ‘crowding effect’). Among more than 12,000 worms recovered, approximately 5 per cent showed one of the following malformations or growth disturbances : (1) Partial twinning (Fig. 1A) : forked posterior strobila ; (2) lateral branching (Fig. 1B) : new tissue outgrowth with varying degrees of differentiation ; (3) dedifferentiation (Fig. 1D) : groups of segments appearing as undifferentiated, vacuolated granular regions ; (4) segment reversal : reversal of normal antero-posterior sequence of proglottides (Fig. 1B) ; (5) combination : dedifferentiation plus branch outgrowth (Fig. 1C ; branch formation with segment reversal (Fig. 1B) ; multiple branching (Fig. 1E).