Biochemical Examination and Identification of Botanicals Active against Adult Anopheles Gambiae from the Coastal Region of Kenya

Abstract

Malaria still remains one of the most important tropical parasitic and vector-borne diseases in terms of geographical distribution, incidence, the extent of the morbidity and mortality. It is endemic in about 100 countries inhabited by >40010 of the world's population with at least 500 million clinical cases reported each year. More than 90% of these cases occur in Africa, where it is one of the most important causes of morbidity and mortality among infants, young children, pregnant women, non-immune travelers, refugees, displaced persons and labourers entering endemic zones. Management of malaria has become more difficult due to the development of resistance by the vectors to a number of once "golden" insecticides and repellents and the spread of resistance to anti-malarial drugs in Plasmodia species. The search for effective vaccines against malaria is still in progress. Personal potection against mosquito bites using repellents and bed nets occupies a central position in the fight against malaria. Human toxicity and allergic reactions have been reported for some commercial available repellents like N, N-diethyl-3-methylbenzamide (DEET). The need for alternative repellents is more urgent than ever before. Plants and their metabolites have been shown to be effective against mosquitoes. Some of the leading repellents and insecticides like pyrethrins are plant-derived or modeled. This justifies further bioprospecting for anti-mosquito products from plants. In the search for new and potent mosquitocides !nd repellents we carried. out)io-evaluation of the Kenyan coastal flora. Essential oils and solvent extracts from aerial parts of 24 plants were evaluated for th~ir repellent and insecticidal acti~ities. Essential oils of 7 plants (Croton pseudopulchellus, Croton menyharthii, Endostemon tereticaulis, Mkilua fragrans, Ocimum fischeri, Ocimum forskolei and Plecranthus longipes) showed good repellent activity (RC5o = 1.515-9.583 X 10-5 rug/em') with 3 (M..fragrans, O.forskolei and P. longipes) also exhibiting significant insecticidal activity (LC50 = 3.044-5.106 X 10-3 rug/em"). Four repellent (carvacrol, 4- propylbenzenemethanol, phytol and thymol) and one insecticidal (carvacrol) principles are reported