Metacestode

Abstract: Among taeniid tapeworms infecting humans through pork or beef, Taenia solium Linnaeus 1758 and Taenia saginata Goeze 1782 have already been known. Based on the morphologic characteristics of adult and metacestodes of Asian Taenia saginata, the third kind of human taeniid tapeworm known to distribute in Asian countries, a new species name of Taenia asiatica is proposed. In addition to the known biology in their intermediate hosts, T. asiatica was different morphologically from Taenia saginata Goeze 1782 in having the unarmed rostellum on the scolex of adult, the large number of 'uterine twigs' and the existence of 'posterior protuberance'. These structures in the gravid proglottids were used as taxonomic keys in taeniid tapeworms for the first time. T. asiatica metacestode (Cysticercus viscerotropica) was different morphologically from T. saginata metacestode (Cysticercus bovis) in having wartlike formations on the external surface of the bladder wall.

Abstract: Host-parasite interactions in the E. multilocularis-intermediate host model depend on a subtle balance between cellular immunity, which is responsible for host's resistance towards the metacestode, the larval stage of the parasite, and tolerance induction and maintenance. The pathological features of alveolar echinococcosis. the disease caused by E. multilocularis, are related both to parasitic growth and to host's immune response, leading to fibrosis and necrosis, The disease spectrum is clearly dependent on the genetic background of the host as well as on acquired disturbances of Th1-related immunity. The laminated layer of the metacestode, and especially its carbohydrate components, plays a major role in tolerance induction. Th2-type and anti-inflammatory cytokines, IL-10 and TGF-beta, as well as nitric oxide, are involved in the maintenance of tolerance and partial inhibition of cytotoxic mechanisms. Results of studies in the experimental mouse model and in patients suggest that immune modulation with cytokines, such as interferon-alpha, or with specific antigens could be used in the future to treat patients with alveolar echinococcosis and/or to prevent this very severe parasitic disease.

Abstract: Taenia parasites have developed elaborate mechanisms of interacting with their intermediate hosts. The oncospheres which invade the intermediate host are susceptible to antibody and complement. However, by the time the host has generated an antibody response, the parasites have begun to transform to the more resistant metacestode. The metacestodes have elaborate means of evading complement-mediated destruction, including paramyosin which inhibits C1q, taeniaestatin which inhibits both classical and alternate pathways, and sulfated polysaccharides which activate complement away from the parasite. Similarly, antibody does not seem to be able to kill the mature metacestode. In fact, the parasites may even stimulate the host to produce antibody, which could be bound via Fc receptors and used as a source of protein. Finally, taeniaestatin and other poorly defined factors may interfere with lymphocyte proliferation and macrophage function, thus paralyzing the cellular immune response. Since the symptoms of NCC are typically associated with a brisk inflammatory response, we hypothesize that disease is primarily caused by injured or dying parasites. This hypothesis raises important questions in assessing the role of chemotherapy in the management of NCC, as well as in the evaluation of clinical trials, most of which were uncontrolled.

Abstract: Background It is believed that in tapeworms a separate population of undifferentiated cells, the germinative cells, is the only source of cell proliferation throughout the life cycle (similar to the neoblasts of free living flatworms). In Echinococcus multilocularis, the metacestode larval stage has a unique development, growing continuously like a mass of vesicles that infiltrate the tissues of the intermediate host, generating multiple protoscoleces by asexual budding. This unique proliferation potential indicates the existence of stem cells that are totipotent and have the ability for extensive self-renewal.