Key words: essential oil nanoemulsion; Xylopia ochrantha; mollusc control; Biomphalaria; schistosomiasis

Schistosomiasis is a disease endemic in several states of Brazil. The population control of the transmitter mollusks is done with Bayluscide WP 70®, in the control programs. OMS preconize molluscicidal assays using Becker with 500 mL of final volume, restringing the number of natural products and synthetic drugs to be tested in function of high quantity of material necessary. A new technique to assess the toxic effects for Biomphalaria sp. is the purpose of this work, for developing adaptation for this aquatic organism, using a low volume of test solution in 24‐well plates. We used Biomphalaria glabrata (10–12 mm size) in a static system, consisting of the following components: Becker containing 10 snails or 24‐well plates where snails were individualized for a volume of 2 mL per well for 24 and 48 hours. For the assays, we added aqueous solutions of Bayluscide WP 70, at a concentration of 1–5 mg/L, distilled water, and 1% dimethyl sulfoxide. Data were evaluated using Kappa’s coefficient, Z factor validation, and comparison study. This technique to assess the toxic effect has proven to be a useful tool to detect lethal and sublethal effects, which could be used as a new evaluation protocol.

Schistosomiasis is a tropical disease transmitted in an aqueous environment by cercariae from the Schistosoma genus. This disease affects 200 million people living in risk areas around the world. The control of schistosomiasis is realized by chemotherapy, wastewater sanitation, health education, and mollusk control using molluscicidal agents. This work evaluates the effects of a nanoemulsion containing essential oil from Myrciaria floribunda leaves as a molluscicidal and cercaricidal agent against Biomphalaria glabrata mollusks and Schistosoma mansoni cercariae. The Myrciaria floribunda essential oil from leaves showed nerolidol, β-selinene, 1,8 cineol, and zonarene as major constituents. The formulation study suggested the F3 formulation as the most promising nanoemulsion with polysorbate 20 and sorbitan monooleate 80 (4:1) with 5% (w/w) essential oil as it showed a smaller droplet size of approximately 100 nm with a PDI lower than 0.3 and prominent bluish reflection. Furthermore, this nanoemulsion showed stability after 200 days under refrigeration. The Myrciaria floribunda nanoemulsion showed LC₅₀ values of 48.11 µg/mL, 29.66 µg/mL, and 47.02 µg/mL in Biomphalaria glabrata embryos, juveniles, and adult mollusks, respectively, after 48 h and 83.88 µg/mL for Schistosoma mansoni cercariae after 2 h. In addition, a survival of 80% was observed in Danio rerio, and the in silico toxicity assay showed lower overall human toxicity potential to the major compounds in the essential oil compared to the reference molluscicide niclosamide. These results suggest that the nanoemulsion of Myrciaria floribunda leaves may be a promising alternative for schistosomiasis control.

Background/objectives: Schistosomiasis is caused by flatworms of the genus Schistosoma, for which mollusks of the genus Biomphalaria are intermediate hosts. Niclosamide (NCL) is a molluscicide recommended by the World Health Organization (WHO) for control of Biomphalaria. Although effective, it is expensive and environmentally toxic, which raises concerns regarding its widespread use. As a result, we explored new synthetic substances as alternative strategies for controlling Biomphalaria glabrata. We evaluated the molluscicidal activity of 2-(1H-py-razol-1-yl)-1,3,4-thiadiazole and 2-(4,5-dihydro-1H-pyrazol-1-yl)-1,3,4-thiadiazole derivatives against B. glabrata snails and embryos, as well as Schistosoma cercariae (infective larvae). Methods: Adult and young snails were added to 24-well plates containing 20 synthetic compounds from the PDAN series for initial screening over 96 h at a concentration of 100 ppm. Water and NCL (2 ppm) were used as the negative and positive controls, respectively. Active compounds in the adult B. glabrata assay were selected for the tests vs. embryos and cercariae. Results: In the initial screen, only PDAN 52 (63 ± 4%) and 79 (12 ± 3%) showed molluscicidal activity at a concentration of 100 ppm up to 48 h. Consequently, we selected only PDAN 52. The LC₅₀ value found in the tests on embryos after 24 h of treatment was 20 ± 2 ppm and, after 48 h, it was 4 ± 0.5 ppm. Against cercariae, we measured an LC₅₀ value of 68 ± 5 ppm after 4 h of treatment. PDAN 52 did not induce marked toxicity against a second mollusk, Physella acuta, after 48 h of exposure. Conclusions: We highlight the promising molluscicidal activity of PDAN 52 against different developmental stages of the mollusk, B. glabrata, as well the infective larvae of Schistosoma mansoni.

Schistosomiasis is a neglected tropical disease caused by parasitic worms of several species of the genus Schistosoma. Transmission occurs by parasitic larvae that stay in freshwater snails of the genus Biomphalaria. Thus, the search for new products that are biodegradable has increased the interest in products of plant origin. The aim of this article is to review the isolated substances from natural products that showed molluscicidal activity against the species Biomphalaria glabrata in order to reevaluate the most promising prototypes and update the progress of research to obtain a new molluscicide. We perform searches using scientific databases, such as Scientific Electronic Library Online (SciELO), Google schoolar, PUBMED, Web of Science and Latin American and Caribbean Literature on Health Sciences (LILACS). From 2000 to 2022, using the keywords “isolated substances”, “molluscicidal activity” and “Biomphalaria glabrata”. In the present study, it was possible to observe 19 promising molluscicidal molecules with a lethal concentration below 20 µg/mL. Of these promising isolates, only 5 isolates had the CL₉₀ calculated and within the value recommended by WHO: Benzoic acid, 2',4',6'-Trihydroxydihydrochalcone, Divaricatic acid, Piplartine and 2-hydroxy-1,4-naphthoquinone (Lapachol). We conclude that beyond a few results in the area, the researches don’t follow the methodological pattern (exposure time and measure units, toxicity test), in this way, as they don’t follow a pattern on the result’s exposure (LC), not following, in sum, the recommended by WHO.

Schistosomiasis is a neglected tropical disease caused by parasitic worms of the genus Schistosoma. In Brazil, there are reports of infection by the Schistosoma mansoni species, which has the Biomphalaria glabrata snail as one of its intermediate hosts. The present work aimed to test the effects of different Abelmoschus esculentus seed extracts and fractions on adults and embryos of B. glabrata and S. mansoni cercariae. A total of four crude extracts and thirteen fractions with different organic solvents were used for the bioassays. The extracts were analyzed using high-performance liquid chromatography coupled to mass spectrometry. Molluscicidal activity was assessed in 24-well plates, after which the LC₅₀ and LC₉₀ were calculated. Assays with B. glabrata embryos and S. mansoni cercariae were also performed. These findings indicate the presence of flavanoids in the hexane, ethyl acetate, and ethanol crude extracts. For the molluscicidal activity assays, eight fractions had an LC₉₀ value less than that recommended by the WHO. The methanol fraction of the dichloromethane extract (FrMeOH EDM) had the most promising results, with an LC90 of 37.15 mg/L and 100% mortality in embryos of B. glabrata and cercariae. FrMeOH, EDM, and other fractions are possible candidates for new drugs for the combat of schistosomiasis.