Failure of auto-infection with Hymenolepis nana in seven inbred strains of mice initially given beetle-derived cysticercoids

Perspectives on intestinal tapeworm infections: An evaluation of direct and indirect life-cycles with a special emphasis on species of Hymenolepis

Numerous experimental studies have been conducted on the rodent tapeworm, Hymenolepis microstoma. In contrast, less is known about the life-cycle and immunobiology of the zoonotic dwarf tapeworm, Hymenolepis nana. However, H. nana appears to be unique in that; (i) it can complete its entire life-cycle within a single mammalian host, and (ii) cysticercoids that develop in beetle intermediate hosts are tailed, while those that develop in the intestinal tissue of mammals are tailless. This is in contrast to all other Hymenolepis spp., which only appear to develop tailed cysticercoids in beetles or experimentally infected immunodeficient rodents. Even though H. microstoma and H. nana are phylogenetically much closer to each other than to Hymenolepis diminuta, when mice with severe combined immunodeficiency (SCID) were inoculated with H. microstoma eggs, hatched oncospheres invaded the intestinal tissue and developed into infective tailed cysticercoids in approximately 11 days. Therefore, H. nana appears to be truly unique in its ability to develop tailed cysticercoids in beetles and tailless cysticercoids in mammals. These unique evolutionary characteristics are discussed in relation to other cyclophyllidean cestodes, including Taenia solium and Echinococcus spp.

Failure to infect laboratory rodent hosts with human isolates of Rodentolepis (= Hymenolepis) nana

Confusion exists over the species status and host-specificity of the tapeworm Rodentolepis (= Hymenolepis) nana. It has been described as one species, R. nana, found in both humans and rodents. Others have identified a subspecies; R. nana var. fraterna, describing it as morphologically identical to the human form but only found in rodents. The species present in Australian communities has never been identified with certainty. Fifty one human isolates of Rodentolepis (= Hymenolepis) nana were orally inoculated into Swiss Q, BALB/c, A/J, CBA/ CAH and nude (hypothymic) BALB/c mice, Fischer 344 and Wistar rats and specific pathogen free (SPF) hamsters. Twenty four human isolates of R. nana were cross-tested in flour beetles, Tribolium confusum. No adult worms were obtained from mice, rats or hamsters, even when immunosuppressed with cortisone acetate. Only one of the 24 samples developed to the cysticercoid stage in T. confusum; however, when inoculated into laboratory mice the cysticercoids failed to develop into adult worms. The large sample size used in this study, and the range of techniques employed for extraction and preparation of eggs provide a comprehensive test of the hypothesis that the human strain of R. nana is essentially non-infective to rodents.

Basic and applied immunology in cestode infections: from Hymenolepis to Taenia and Echinococcus

In larval cestode infections, it is well established that the intermediate mammalian host infected with egg-derived metacestodes in the tissue becomes completely immune to reinfection with eggs, whereas autoinfection has been conceived to occur in Hymenolepis nana/mouse (and human) and Taenia solium/human systems when these hosts are initially infected with metacestode-derived adult tapeworms in the lumen. In this review paper, the first topic is immunobiology of H. nana/mouse system on the reinfection immunity in order to get critical information as to how the initially ingested parasite (eggs or metacestodes) can develop into adult worms and how autoinfection does or does not occur in immunocompetent mice, since H. nana can complete its whole life cycle in the mouse intestinal tissue and lumen. When mice are infected with eggs (= oncospheres) of H. nana, they become immune to challenge infections with eggs within a few days (early response) and with cysticercoids within two weeks (late response). The initially established adult worms are expelled later (worm expulsion response). When mice are infected with cysticercoids, either derived from beetles or mice, they become immune to challenge infection with cysticercoids but not with eggs. Therefore, autoinfection occurs in the intestinal tissue for the establishment of cysticercoids in the tissue but never occurs in the intestinal lumen for the establishment of adult worms in immunocompetent mice. The second topic is vaccination trial against challenge infection with eggs of Asian Taenia in pigs. Pigs vaccinated with frozen oncospheres of Asian Taenia from Taiwan or Korea or T. saginata showed very strong resistance, whereas pigs vaccinated with those of T. solium showed partial resistance only. It is suggested that Asian Taenia is much closer to T. saginata than T. solium from the immunobiological viewpoint. The third topic is immunodiagnosis of echinococcosis and cysticercosis. Immunoblot analysis has revealed that Em18 (18 kDa component of crude antigens of Echinococcus multilocularis protoscolex) and glycoproteins of T. solium cysticerci are highly specific or unique to alveolar echinococcosis and cysticercosis, respectively. The fourth topic is discussion on miscellaneous prospects including laboratory animal models for echinococcosis and cysticercosis.