Potassium usnate toxicity against embryonic stages of the snail Biomphalaria glabrata and Schistosoma mansoni cercariae.

The snail Biomphalaria glabrata is the most important vector for Schistosoma mansoni. Control of this vector to prevent the spread of schistosomiasis is currently performed with the application of a niclosamide molluscicide, which is highly toxic to the environment. Screening of substances that show embryotoxic molluscicidal potential as well as have detrimental effects on cercariae is very relevant for the control of schistosomiasis, as the efficacy of prevention of the disease is increased if it acts as a molluscicide as well as on the cercariae of S. mansoni. The aim of this work was to evaluate the effect of potassium usnate derived from usnic acid on different stages of embryonic development of B. glabrata and on S. mansoni cercariae. After 24 h of exposure, potassium usnate showed embryotoxic activity across all embryonic stages. The values obtained from the LC50 for the embryonic stages were the following: blastula 5.22 µg/mL, gastrula 3.21 µg/mL, trochophore 3.58 µg/mL, veliger 2.79, and hippo stage 2.52 µg/mL. Against S. mansoni cercariae, it had LC90 and 100% mortality at concentrations of 2.5 and 5 µg/mL in 2 h of exposure. In conclusion, this is the first report of potassium usnate toxicity on the embryonic stages of B. glabrata and cercariae of S. mansoni, and this study shows the potassium usnate as a promising agent for the control of mansoni schistosomiasis.