Echinococcus: the model cestode parasite

Abstract

Cestodes are important endoparasitic organisms, some of which are responsible for serious zoonotic diseases. The most severe diseases are inflicted by the larval stages (metacestodes) of Echinococcus multilocularis and E. granulosus sensu lato (s. l.), which are the causative agents of alveolar (AE) and cystic echinococcosis (CE), respectively. Another member of the Taeniidae family, Taenia solium, has also a prominent role as the causative agent of cysticercosis, with a special importance for neurocysticercosis (NC). The adult-stages of these parasites colonialize the intestine of their definitive hosts, which are foxes and dogs for E. multilocularis, canines for E. granulosus and humans for T. solium. In the intestine of the definitive host, selfor cross-fertilization of adults leads to the production of eggs which contain a zygote, eventually forming a pre-larval stage (oncosphere), which is then accidentally ingested by an intermediate host. CE and AE have been historically considered as food-and water-borne infections, with more recent evidence also pointing to the importance of hand-to-mouth transmission, and they are ranked as the most important foodborne parasites worldwide (Tamarozzi et al. 2020;Torgerson et al. 2020). For Echinococcus spp. and T. solium, several mammalian species can be infected as intermediate hosts, including humans, which act as dead-end hosts for E. granulosus and E. multilocularis. Within their intermediate hosts, the parasite larvae are usually targeted to distinct compartments or organs, such as the liver in most cases for E. multilocularis infections or liver and lungs for E. granulosus. In the case of T. solium infections, the most serious consequences occur upon invasion of the central nervous system, which less commonly also can be caused by Echinococcus spp. There, development into the larval metacestode (Echinococccus spp.) or cysticercus (T. solium) stage takes place, which causes disease due to expansion, extensive proliferation and/or inflammatory reactions on part of the host. Besides Echinococcus spp. and Taenia spp., there are a number of other, albeit less prominent, cestodes that exhibit a considerable zoonotic potential. A more recently, identified cestode causing disease in humans was identified in human cases in North America, causing systemic infection of organs and blood vessels (Deplazes et al. 2019). Metacestodes exhibited molecular hallmarks that resembled, but were clearly distinct from, Vesteria mustelae. Vesteria mustelae parasitizes weasels and has not been demonstrated to be zoonotic, indicating that previously unrecognized human pathogenic cestodes species with still unknown potential animal hosts exist (Deplazes et al. 2019). Other species causing disease in humans include Hymenolepis and Dibothriocephalus, but also Bertiella, Dipylidium, Raillietina, Inermicapsifer and Mesocestoides. As indicated in a recently published review, the true clinical significance of these less prominent tapeworms is not well known, as they are often more difficult to iden...

Targeted and non-targeted proteomics to characterize the parasite proteins of Echinococcus multilocularis metacestodes

“…For the development of novel anti-echinococcal therapies, the key of success resides in the understanding of the biology of the disease-causing stage of Echinococcus , the metacestode. Since in vitro culture systems exist for E. multilocularis , this parasite may be considered as a model for other cestodes ( Hemphill and Lundstroem-Stadelmann, 2021 ). In particular, the host–parasite interplay can be studied using this system in vitro as well as in in vivo mouse models that represent natural hosts of the parasite ( Brehm and Koziol, 2017 ).…”

In Vitro Activities of Dithiocarbamate Derivatives against Echinococcus multilocularis Metacestode Vesicles

“…Whole-organism-based screening plays an important role in the search for new antiparasitic drugs and is used to screen for active compounds against various helminths [ 18 ]. The repurposing of drugs that are licensed for the treatment of other diseases can reduce the time and costs of treatments to reach patients of neglected diseases including AE [ 19 , 20 ]. The drug disulfiram has been used in human patients to treat chronic alcoholism [ 21 , 22 ].…”

Establishment and application of unbiased in vitro drug screening assays for the identification of compounds against Echinococcus granulosus sensu stricto

“…multilocularis represents a model cestode, due to the fact that in vitro culture of metacestode vesicles and isolated GL cells (including parasite stem cells) has been established, and options for genetic manipulation by RNAi were introduced [ 25 , 26 ]. In addition, parasite isolates can be passaged in mice and cryopreservation protocols are implemented [ 27 – 30 ]. While older studies on the evaluation of drug effects against E .…”

“…multilocularis represents a model cestode, due to the fact that in vitro culture of metacestode vesicles and isolated GL cells (including parasite stem cells) has been established, and options for genetic manipulation by RNAi were introduced [25,26]. In addition, parasite isolates can be passaged in mice and cryopreservation protocols are implemented [27][28][29][30]. While older studies on the evaluation of drug effects against E. multilocularis relied on subjective microscopic assessments, the more advanced culture techniques for E. multilocularis enabled researchers to develop a drug screening cascade for the discovery of novel compounds or repurposed drugs, which uses objectively measurable methodology [24].…”