Physiological changes in Biomphalaria glabrata say, 1818 (Pulmonata: Planorbidae) caused by sub-lethal concentrations of the latex of Euphorbia splendens var. hislopii N.E.B (Euphorbiaceae)

Abstract

Molluscides have been used as one of the strategies to control schistosomiasis. Many plant extracts with molluscidal effects have been tested, but the action of the latex of Euphorbia splendens var. hislopii is considered the most promising because it meets the recommendations of the World Health Organization (WHO). The objective of this study was to determine the lethal dose and identify the effects of the different doses of latex of E. splendens var.hislopii on the physiology of Biomphalaria glabrata submitted to treatment for 24 h. The concentrations of glucose, uric acid and total proteins in the hemolymph and of glycogen in the digestive gland and cephalopodal mass were determined. The LD 50 value was 1 mg/l. The highest escape index was found to be at a concentration of 0.6 mg/l. The results showed that the latex of E. splendens var. hislopii caused a sharp reduction in the reserves of glycogen in the digestive gland and elevation of the protein content in the hemolymph of B. glabrata. Key words: plant molluscide -Euphorbia splendens var. hislopii -Biomphalaria glabrataThe use of molluscides as one of the strategies to control schistosomiasis began in Brazil in 1976, with the creation of the Special Schistosomiasis Control Program by the National Health Foundation (Machado 1982). The product used in the program was niclosamide, an ethanolamine salt of 2',5-dichloro-4'-nitrosalicylanilide, manufactured under the trade name Bayluscide  , whose efficacy had previously been established (Gonnert 1961). Application of this product caused biocidal action on non-target plants and animals (Andrews et al. 1983), besides causing genotoxicity and carcinogenic effects (Vega et al. 1988). The high cost (Pieri 1995), the possibility of recolonization of breeding grounds (Sarquis et al. 1997(Sarquis et al. , 1998, and the ecological toxicity of this product were limitations on its use as an official molluscide in government programs to control schistosomiasis.At the same time, various plants were tested as natural molluscides. Jurberg et al. (1989) (Mendes et al. 1984). Of these, E. splendens stands out for its molluscidal activity in doses under 0.5 mg/l, eight times smaller than the lethal dose for fish (Vasconcellos & Schall 1986).Some questions have arisen in the selection of plant molluscides, such as: toxicity, availability, annual growth, adaptability to different local conditions, and location of molluscidal activity in parts of the plant that easily regenerate, such as the leaves. To be eligible for use, a product must be storable and remain viable for at least one year; be physically and chemically stable; have ethnobotanical value; and be easy to extract and apply, preferably in aqueous extracts (Kloos & McCullough 1982). Considering all these criteria, in 1998 the Oswaldo Cruz Institute (IOC, Fiocruz, RJ) obtained a biotechnology patent on a method to collect, extract and apply E. splendens var. hislopii latex as a molluscide (Vasconcellos 2000).In the published works on plants with molluscidal action and ...

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