Developmental Physiology of Cestodes. III. Development of Hymenolepis diminuta in Superinfections

The development of Hymenolepis diminuta (Cestoda: Cyclophyllidea) as affected by a preexisting H. diminuta infection was studied, and the fate of worms in crowded infections was determined after periods up to 5 months. When rats with mature primary infections of various intensities are superinfected with 10 cysticercoids, and the worms recovered 10 days after secondary infection, weights of individual secondary worms are inversely proportional to the numbers of primary worms present. Secondary worm recovery is slightly lower with increasing numbers of primary worms, but many secondary worms establish themselves in all cases studied. When rats with secondary infections are followed for longer periods, secondary worms eventually increase in size and merge indistinguishably with the primary population, whether the primary infection is of low density or crowded. However, initial growth rate of secondary worms is depressed and maturation is delayed. When crowded (50 cysticercoids/rat) infections are followed up to 5 months, there is often a spontaneous loss of part of the infection. Available evidence for the existence of premunition in cestode infections is reviewed, and avoidance of the term "premunition" with reference to lumen-dwelling cestodes is suggested.