Molluscicidal effect of three monoterpenes oils on schistosomiasis and fascioliasis vector snails in Egypt

ABSTRACT

Thymol, Linalool and Eugenol showed considerable molluscicidal effect against Biomphalaria alexandrina, Bulinus trancatus and Lymneae natalensis. The thymol was the potent one at least LC 50 and LC 90 followed by euganol then linalool. L. natalensis were mole sensitive to these compounds followed by B. truncatus and then B. alexandrina. The LC 50 and LC 90 of thymol were 22 and 34 ppm against B. alexandrina, 20 and 30 ppm for B. truncatus and 1 8 and 29 ppm for L. natalensis. These values were higher with Eugenol, 28 and 48 ppm for B. alexnadrina, 24 and 44 ppm for B. truncatus and 22 and 40 ppm for L. natalensis. Linalool showed highest values of LC 50 and LC 90 against B. alexandrina, 34 and 56 ppm, against B. truncatus 30 and 52 ppm and for L. natalensis 28 and 48 ppm, respectively. Maintaining of B. alexandrina at LC 10 of Thymol for one week induced an inhibitory effect in the level of some enzymes [AchE, SDH]. It led to increase in the activity of other enzymes [ACP, ALP and G-6-PD]. Acetylcholine-sterase activity [AchE] of treated B. alexandrina was significantly reduced by 45.9% when compared to control. The results showed a significant decrease in succinate dehydrogenase activity [SDH] by 46.4% together with a concomitant increase in glucose-6-phosphate dehydrogenase activity level [G-6-PD] by 47.5% in comparison with control. The activities of acid phosphatase and alkaline phosphatase enzymes were found to be higher in the treated snails than in control ones. The percentage increases were 47.2% and 73.2% respectively. The results also showed an elevation in the hemolymph glucose content of treated snails by 51.9% while the tissue glycogen content was reduced by 48.1%. The infection of B. alexandrina with S. mansoni miracidia was greatly reduced by thymol LC 10 [sublethal dose]. The infection rate reduction was 43.1%. The treated snails' prepatent period was prolonged [34.2 +/- 3.3 days] compared to control [28.4 +/- 1.2 days]. A highly significant reduction of total cercarial production per snail occurred in experimental snails as compared to control