Protoscolices of Echinococcus granulosus were incubated in vitro with praziquantel (PZ), albendazole (ABZ), or a combination of both (PZ + ABZ). PZ and ABZ displayed slower protoscolicidal activity when applied separately than when used in combination. Despite the low PZ + ABZ concentrations used, protoscolex viability dropped rapidly (within 15 days). At this time, cysts did not develop following their inoculation into mice. The ultrastructural changes induced in the protoscolices by PZ + ABZ were (a) the loss of sucker concavity, (b tegumental contraction of the soma region, (c) the formation of digitiform tegumental extensions, (d) destruction of the tegument, and (e) the degeneration of parenchyma cells as reflected by the presence of numerous lamellar bodies. The PZ + ABZ treatment was effective only against small cysts, which had collapsed at 10 days postinoculation (p.i.). This treatment caused the following alterations: (a) loss of cyst turgidity at 6 days p.i.; (b) separation of the laminated and germinal layers; (c) loss of microtriches; (d) the appearance of numerous lipid droplets in the inner region of the germinal layer, (e) vacuolation of the cyton cytoplasm; and (f) the formation of abundant autophagosomes, which finally led to loss of the integrity of the germinal layer.

The efficacy of praziquantel against the metacestode of Echinococcus granulosus was studied by means of in vitro incubations or in vivo experiments. The results of in vitro incubations indicated that the effectiveness of praziquantel was higher when the parasite material comprised cysts from cyst masses than in the case of intact cysts that retained their adventitial layer. Ultrastructural alterations in the germinal layer of collapsed cysts incubated in vitro were detected. The results obtained in mice after 4 months of treatment demonstrated no significant difference between the control and treated groups with regard to the number and wet weight of developed cysts. However, ultrastructural alterations were detected in the cyst tissue that were similar to those described in the in vitro experiment. In contrast, the effect of chemoprophylaxis on the number and the wet weight of developed cysts was extremely significant as compared with the control value, the efficacy being 99.41% and 98.32%, respectively. Moreover, ultrastructural observations of the cyst tissue revealed loss of its integrity, and no intact cyton was observed in the germinal layer of the developed cyst.

The ultrastructure of the papillae and presumed sensory receptors in the tegument of the scolex of Gymnorhynchus gigas plerocercoid were investigated by scanning and transmission electron microscopy. Four distinct types of putative sense receptor (including three uniciliated and one nonciliated) are described for the first time in G. gigas, and this investigation is the first detailed ultrastructure study of tegumental receptors carried out in trypanorhynch cestodes. Microtriches arranged in clusters with a dome-shaped pattern seemed to be papillae that contained a ciliated sensory receptor (type I). The density of these papillae was greater in the center of the bothridial adherent surface near the tentacle orifice than in the lateral margins of the bothridia or in the pars post-bothridialis. The type I receptor is characterized by a long cilium anchored in the nerve bulb by a dense basal body but lacks rootlets. The bulb contains one or two electron-dense collars, numerous electron-lucent neurovesicles, and some mitochondria. The type II receptor presents a short cilium retracted into an invagination of the tegument that arises from the basal body. The bulb contains one electron-dense collar and numerous electron-lucent vesicles, but the rootlets are absent. The type III receptor is also a ciliated receptor embedded in a bulb wider than that of types I and II, and it differs from type II in that it possesses two electron-dense collars and small rootlets associated with the basal body. No electron-lucent vesicle was found in the bulb of this type III receptor. The type IV receptor is a nonciliated receptor localized under the surface with no contact to the outside. It consists of a flattened bulb that contains two electron-dense collars and striated rootlets associated with a band of microfilaments. A comparison of the ultrastructural features of receptors in different cestodes is presented.

The efficacy of ivermectin (IVM) alone, albendazole (ABZ) alone and a combination of both (IVM + ABZ) against Echinococcus granulosus protoscolices was studied by means of in vitro incubation. The maximum protoscolicidal effect was detected when we used IVM+ABZ in combination. In this case, protoscolex viability dropped to 35% in comparison with 50% for IVM alone and 82.5% with ABZ alone 18 days post-incubation. Only the protoscolices incubated with IVM + ABZ did not develop into cysts following their inoculation into mice. The changes in ultrastructure induced in the protoscolices after the different drug incubations are also described. The incubation of cysts with IVM and IVM + ABZ shows that IVM + ABZ in combination is more effective than IVM alone as only when we incubated the cysts with IVM + ABZ did they completely lose their infectivity to mice. This occurred after only 10 days post-incubation. Cellular alterations were also more marked with IVM+ABZ incubations with: (1) the presence of residual bodies, (2) numerous lipids droplets and (3) vacuoles in the cytoplasm of cytons. However, the truncated microtriches and the nuclei remained unaltered after 10 days.

The combination of praziquantel and albendazole (PZ + ABZ) used in the present study demonstrated an efficacy of 100% when used as chemoprophylactic treatment because no viable hydatid cysts developed after mice had been injected with protoscolices. However, when the PZ + ABZ combination was used for the treatment of 4-month secondary experimental hydatidosis, no significant difference was found between the control and treated mice, although severe damage to the cyst ultrastructure of the treated mice was observed.