Physiological changes and molluscicidal effects of crude latex and Milin on Biomphalaria glabrata
Introduction
Schistosomiasis is a major cause of morbidity and mortality in developing countries including Africa, South America, the Caribbean, the Middle East, and Asia (Chitsulo et al., 2000). However, the increase in immigration and tourism to these endemic areas, cases of schistosomiasis are now occurring throughout the world (Chitsulo et al., 2000). This disease is recognized as one of the major communicable diseases of public health and socio-economic importance in the developing world (WHO, 1998). Despite numerous control efforts in a number of countries, still an estimated 200 million people are infected, out of which 120 million are symptomatic and 20 million have severe debilitating disease (WHO, 1983, WHO, 1984, WHO, 1998). Molluscicides have been used as one of the strategies to control schistosomiasis by the reduction of the intermediate host snails of the parasite Schistosoma mansoni from the fresh water reservoirs (Andrews et al., 1983). The study of the molluscicidal physiology of the snail organisms is on going but some reports indicate that the molluscicides act by disrupting the osmoregulatory mechanisms of the epithelial cells (Brackenbury, 1999).
The control of snail population with molluscicides has been one of the most effective methods of reducing the risk of schistosomiasis transmission in endemic area (Mc Cullough, 1992). The niclosamide, a synthetic molluscicide is recommended from the WHO for large scale use in schistosomiasis control program (WHO, 1998). However, the high cost of synthetic molluscicides, their toxicity to non-target organisms and the development of resistance in snail population have led a demand for cheaper and safer alternatives (Lemmich et al., 1995, Pointier and Giboda, 1999). Therefore, it is important to find natural molluscicides that could be effective, cheaper and easily available.
Ethnopharmacological literature and traditional folk medicine provides such information about plant species exhibiting molluscicidal activity. Latex of several members of the family Euphorbiaceae shows higher molluscicidal activity than that of any synthetic molluscicides (Singh and Agarwal, 1984). Among the Euphorbia spp, the latex of Euphorbia milii was found to be the most effective (Vasconcellos and Schall, 1986, Mendes et al., 1997, Schall et al., 1998). This latex has been reported on the lethality of the snail as well as against the cercaria of S. mansoni (Marston and Hostettmann, 1985). The adequate lethality of E. milii latex against B. glabrata snails and larval stage of S. mansoni makes it a potential alternative molluscicide (De-Carvalho et al., 1998). Several reports were available on the molluscicidal action of E. milii latex such as the effect of pH on the molluscicidal activity of latex (Vasconcellos and Amorim, 2003); physiological changes in snail and the effect of latex on the parasite larvae (De-Carvalho et al., 1998) and photodegradation of the latex (Oliveira Filho and Paumgartten, 1997). No studies on the molluscicidal activity of specific compounds or components of E. milii latex on the population of snails are reported. E. milii latex contains toxic physiologically active constituents. A search for useful biochemical constituents of the latex with molluscicidal action yielded multiple proteins. Milin, a serine protease with novel properties was one of them (Yadav et al., 2006).
The central objective of this study was to find out the specific compound in the latex responsible for the lethality of the snails. The effect of different components of the latex of E. milii together with serine protease Milin was reported in this study.
Section snippets
Animals
The mollusks were collected from the field using forceps, and were placed in aplastic bowls with dampened gauze and thereafter transported to the laboratory. The mollusks were kept in illuminated glass flask filled with small amount of water and examined for physiological conditions. The collected animals were kept in glass aquaria containing 20 l de-chlorinated tap water for acclimatization to laboratory conditions. The mollusks of 5–9 mm in shell length were used for each toxicity assay. The
Toxic effect of crude and processed latex on snails
The result of toxic effect of crude latex (with gum) and processed latex (after removal of the gum) on the young specimen of the snails B. glabrata were presented in Fig. 1. A total 20 adult snails were placed in each of three aquariums. The first one was control and other two contain 0.1% of either crude or processed latex respectively. The death of snail population started after second day of treatment and all animals were dead within 7 days of treatment. Median mortality time was achieved in
Discussion
Molluscicidal activity is known to be widespread in the family Euphorbiaceae, although this activity varies greatly with respect to species, plant part selected, and even method of extraction (Vasconcellos et al., 1999). The latex of the Euphorbia milii is a well known molluscicide and is frequently used to control the disease schistosomiasis by the reduction of the intermediate host Biomphlaria glabarata from the water reservoir in developing countries like Brazil, Egypt, China and India (
Conclusion
Different components of the E. milii latex show diverse physiological and lethal behaviour on fresh water snail Biomphlaria glabarata. Molluscicidal action of the latex is due the collective action of different latex constituents on intermediate host snail. Neither proteinaceous nor non-proteinaceous fraction separately illustrates the effective molluscicidal action. However, Milin isolated from the latex with small amount of non-proteinaceous fraction showed similar molluscicidal action as
Acknowledgments
The financial assistance from Council of Scientific and Industrial Research, Government of India, in the form of research fellowship to SCY is acknowledged. Infrastructure facilities are funded by University Grants Commission, and Department of Biotechnology, Government of India is acknowledged.
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