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Title: A NEW IN VITRO BIOASSAY SYSTEM FOR DISCOVERY OF NOVEL HUMAN-USE MOSQUITO REPELLENTS.

Author
item KLUN, JEROME
item KRAMER, M. - USDA, ARS, BCS
item DEBBOUN, M. - U.S. ARMY

Submitted to: American Mosquito Control Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2004
Publication Date: 3/16/2005
Citation: Klun, J.A., Kramer, M., Debboun, M. 2005. A new in vitro bioassay system for discovery of novel human-use mosquito repellents.. American Mosquito Control Association. 21:64-70.

Interpretive Summary: Serious diseases such as West Nile Virus, malaria, dengue fever, and yellow fever are transmitted to humans by blood-feeding mosquitoes, and there is a need to discover new effective topically applied mosquito repellent compounds for protection of humans against these disease carriers. To find new repellents, one might apply test chemicals to the skin of humans in the presence of feeding mosquitoes. However, this approach is not possible because often times the safety of test chemicals for human use is unknown. This toxicological limitation severely restricts chemical screening programs for discovery of new and effective arthropod repellents for human use. To overcome this limitation, we designed and developed a blood-feeding membrane system that mosquito feed upon as if it were a human. Tests showed that when commercial repellents were applied to the blood-feeding membrane, repellent activities closely resembled results obtained when the commercial compounds were applied to humans. Thus, the new blood-feeding membrane system can be used to cheaply and quickly screen large numbers of compounds with unknown toxicity, and to identify new effective human-use repellent candidate compounds. Promising compounds discovered in this way can be toxicologically evaluated, and if found safe, they would be ultimately developed for human use as new protectants against disease-carrying mosquitoes.

Technical Abstract: A K & D test module, previously developed and used for quantitative measurement of the efficacy of mosquito repellents on human subjects, was adapted for in vitro evaluation of repellents by coupling the module with a membrane-blood reservoir. Performance of Deet, Bayrepel® and SS-220, insect repellents in the new in vitro system, was compared with their performance on humans against mosquitoes. For each compound, in vitro dose-response assays were conducted with compounds applied to cloth positioned over blood reservoirs covered with Baudruche membrane against Aedes aegypti (L.). The repellents were also tested in vitro against Anopheles stephensi Liston and Ae. aegypti at a fixed dose of 24 nmol compound/cm2 cloth over the Baudruche membrane and an Edicol collagen membranes. At the same time, the repellents were tested at the fixed dose using the K & D module on human volunteers. The observed proportions of mosquitoes deterred from biting in the dose-response and the fixed doses in vitro assays showed that assay results were statistically identical to those obtained using humans in all tests against both mosquito species. This new in vitro assay system can be used in high through-put screening of compounds to identify new repellents having potential for use as topical mosquito repellents on humans.