Persistence of regenerative stem cells provides a cellular basis for the parasitostatic activity of albendazole against Echinococcus multilocularis

Albendazole (ABZ) is the mainstay of chemotherapy for alveolar echinococcosis caused by the larval stage of Echinococcus multilocularis, but its activity is predominantly parasitostatic rather than parasiticidal. The cellular basis of this remarkable parasite persistence remains poorly understood. Here, we investigated the effects of sustained ABZ exposure on the germinative stem cells that drive metacestode growth and regeneration and examined whether differential beta-tubulin isoform usage could contribute to their drug susceptibility. ABZ rapidly impaired microtubule-dependent tegumental transport and caused pronounced damage to metacestode vesicles. In contrast, proliferative germinative cells (GC) persisted during prolonged and continuous ABZ exposure. Importantly, cells surviving 14 to 28 days of treatment retained developmental competence, regenerated metacestode vesicles following drug withdrawal, and, after extended exposure to 10 micromolar ABZ, remained capable of generating parasite tissue following transplantation into a permissive host. Transcriptomic and immunohistochemical analyses identified the Y200 containing beta tubulin isoform Tub2 as a major metacestode beta tubulin that is almost exclusively associated with the proliferative GC lineage. Tub2 was present in virtually all S phase cells, colocalized with established GC markers, localized to mitotic spindles, and Tub2+ cells persisted during prolonged ABZ and ABZSO exposure. Structural analysis further revealed an E198-Y200 interaction in Tub2, providing a structural correlate of the resistance-associated Y200 configuration. Together, these findings provide a cellular explanation for the predominantly parasitostatic activity of benzimidazoles against E. multilocularis. ABZ profoundly damages parasite tissue while sparing a regenerative cell compartment capable of re-establishing metacestode growth after drug withdrawal. They further identify GC-associated Tub2 as a plausible molecular contributor to this persistence and as a potential target for curative anti-Echinococcus chemotherapy.