Evaluation of praziquantel effects on Echinostoma paraensei ultrastructure

Echinostomiasis is a food-borne, intestinal, zoonotic, snail-mediated helminthiasis caused by digenean trematodes of the family Echinostomatidae with seven species of the genus Echinostoma infecting humans or domestic and wildlife animals. Echinostoma paraensei is a peristomic 37-collar-spined echinostome belonging to the "revolutum group". Praziquantel (PZQ) is the drug of choice for treatment and control of human schistosomiasis and food-borne trematodiasis. In the present study we used scanning and transmission electron microscopy to further elucidate the trematocidal effect of PZQ on adult E. paraensei and confirmed that this trematode is a suitable model to study anthelmintic drugs. Hamsters infected with E. paraensei were treated with a single dose of 30 mg kg(-1) of PZQ. The worms were recovered 15, 30, 90 and 180 min after drug administration. There was a significant decrease in worm burden in the small intestine in the hamster-E. paraensei model at the intervals of 30, 90 and 180 min after the treatment. The worms displayed damage of the peristomic collar with internalization of the spines and erosion of the tegument of the circumoral head-collar of spines. Ultrastructural analysis demonstrated an intense vacuolization of the tegument, appearance of autophagic vacuoles and swelling of the basal infolds of the tegumental syncytium. There was no change in the morphology of cells from the excretory system of adult E. paraensei, however, there was an apparent decrease of stores of glycogen particles in parenchymal cells in PZQ-treated worms. Our results demonstrated that PZQ promotes surface and ultrastructural damage of the tegument of adult E. paraensei supporting the idea that this trematode may constitute a good model to investigate drug effects mechanisms in vitro and in vivo.