Effect of an intraperitoneal injection with activated Hymenolepis nana and H. diminuta cysticercoids on homologous challenge.

The intraperitoneal injection of excysted-activated cysticercoids of Hymenolepis nana and H. diminuta stimulates a protective immunity in mice and rats against an oral homologous challenge with different levels of effectiveness. The immunizing dose reduced only worm growth in the natural host (i.e. H. nana/mouse and H. diminuta/rat models), while in the unnatural host (i.e. H. diminuta/mouse model) expulsion of the worms from the intestine was accelerated. In mice infected with H. nana the effect appeared about 20 days after injection, but a greater effect was found in both models 40 days later even at low dose (1 cysticercoid). In rats the effect appeared 40 days after injection when a large inoculum (50 or 100 cysticercoids) was used. The induced immunity was slow in developing and only partially effective: this was probably related to host difficulties in processing somatic worm antigens, or to the slow production of metabolites by the worms in the peritoneal cavity.