THE SUSCEPTIBILITY OF RECENT ISOLATES OF Schistosoma mansoni TO PRAZIQUANTEL

Abstract

Introduction: Schistosomiasis is a chronic disease caused by trematode flatworms of the genus Schistosoma and its control is dependent on a single drug, praziquantel (PZQ), but concerns over PZQ resistance have renewed interest in evaluating the in vitro susceptibility of recent isolates of Schistosoma mansoni to PZQ in comparison with well-established strains in the laboratory.

Material and methods: The in vitro activity of PZQ (6.5-0.003 µg/mL) was evaluated in terms of mortality, reduced motor activity and ultrastructural alterations against S. mansoni.

Results: After 3 h of incubation, PZQ, at 6.5 µg/mL, caused 100% mortality of all adult worms in the three types of recent isolates, while PZQ was inactive at concentrations of 0.08-0.003 µg/mL after 3 h of incubation. The results show that the SLM and Sotave isolates basically presented the same pattern of susceptibility, differing only in the concentration of 6.5 µg/mL, where deaths occurred from the range of 1.5 h in Sotave and just in the 3 h range of SLM. Additionally, this article presents ultrastructural evidence of rapid severe PZQ-induced surface membrane damage in S. mansoni after treatment with the drug, such as disintegration, sloughing, and erosion of the surface.

Conclusion: According to these results, PZQ is very effective to induce tegument destruction of recent isolates of S. mansoni.

Fig. 1A-G. - Male and female adult worms of Schistosoma mansoni (BH strain) control processed to scanning electron microscopy. A) Male with presence of oral sucker (os), ventral sucker (vs) and gynecophoral canal (gc). B) Distribution of the tubercles (tu) along the body and sensory papillae (open arrows). C) Caudal portion of the male worm. D) Tubercle detail with spines (sp). E) Female with presence of oral sucker (os) and ventral sucker (vs). F) Smooth body of female without tubercles. G) Caudal portion of the female worm.

Fig. 2A-F. - Male and female adult worms of S. mansoni (SOT strain) treated with 6.5 µg/mL PZQ after 3h incubation.Male: A) Coiled worm. C) Severe vacuolization of the tegument. E) Collapse of the tubercles, erosion and exposure of internal muscles. Female: B) Wrapped worm. D) Female worm, destruction and peeling of the tegument surface. F) Exposure of internal muscles.

Fig. 3A-F. - Male and female adult worms of S. mansoni (BH strain) treated with 6.5 µg/mL PZQ after 3h incubation.Male: A) Coiled worm. C) Severe vacuolization of the tegument. E) Collapse of the tubercles, erosion and exposure of internal muscles. Female: B) Wrapped worm. D) Extensive sloughing (sl) exposing to view the basal membrane (bm). F) Exposure of internal muscles.

Fig. 4A-F. - Male and female adult worms of S. mansoni (SLM strain) treated with 6.5 µg/mL PZQ after 3h incubation. Male: A) Coiled worm. C) Severe vacuolization of the tegument. E) Collapse of the tubercles, erosion and exposure of internal muscles. Female: B) Wrapped worm. D) Extensive sloughing (sl) exposing to view the basal membrane (bm). F) Exposure of internal muscles.