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REDUCTION OF INFECTIVITY OF SCHISTOSOME CERCARIAE BY APPLICATION OF CERCARICIDAL OIL TO WATER

Schistosomiasis continues to plague populations living in disease-endemic areas, and exposure to infective cercariae results in more than 200 million cases worldwide. Laboratory experiments were conducted to test whether a cercaricidal film applied directly to the water surface can reduce viability of cercariae. A distillate from inexpensive cedarwood oil enriched for cedrol in a mixed oil fraction was formulated (1:5) with the surfactant Tween 80. When applied to the surface of clean and turbid water in test vessels, the formulation spread across and just below the air-water interface, causing inactivation of Schistosoma mansoni cercariae within minutes. The active ingredient was heat stable and reduced schistosome survival and infectivity by 90% and 99.2%, respectively in a mouse model. The effective dose (13 µg/cm²) was dependent on surface area rather than volume of water treated. We conclude that application of the biodegradable formulation to the surface of schistosome-infested waters may be an effective, economical, and safe means of reducing human infections.

Received May 17, 2005. Accepted for publication July 21, 2005.

Acknowledgments: We are grateful to Dr. F. Lewis (Schistosomiasis Laboratory, Biomedical Research Institute, Rockville, MD) for supplying the infected Biomphalaria glabrata snails used in this work and his assistance with perfusion studies through the National Institutes of Health–National Institute of Allergy and Infectious Diseases contract AI-30026. We also thank Dr. Paul Miller (Department of Biochemistry, Johns Hopkins Bloomberg School of Public Health) for assistance and guidance with the distillation of red cedarwood oil for production of the MOF, Dr. James Polli (Department of Pharmaceutical Sciences, University of Maryland, School of Pharmacy, Baltimore, MD) for guidance and suggestions, and Jochen Heidler and Jacqueline Heilman for analysis of cedar oil components by GC/MS.

Financial support: This work was supported by technology transfer grant 040-950-0163 from Johns Hopkins Bloomberg School of Public Health and by NIH training grant T32 AI 07417 (Training in Molecular and Cellular Bases of Infectious Disease).

^* Address correspondence to Jean Marie Naples, Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD 21205-2179. E-mail: jnaples{at}jhsph.edu

Authors’ addresses: Jean Marie Naples and Clive Shiff, Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205-2179. Rolf U. Halden, Department of Environmental Health Sciences, Center for Water and Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205-2179.