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dc.contributor.authorVulule, John M
dc.descriptionDoctor of Philosophyen
dc.description.abstractAnopheles gambiae sensu lato and Anopheles funestus were collected from villages with permethrin impregnated bednets or curtains (0.5gm/m2 ), villages with no intervention measures and from the Ahero Rice irrigation Scheme by two methods: the resting collection (RC) and human bait collection (HBC). These mosquitoes were assayed for susceptibility to permethrin and other insecticides using the conventional WHO test kit and cone. An. gambiae s.l. mosquitoes were speciated by the Polymerase chain reaction method (PCR). A colony of permethrin resistant An. gambiae sensu stricto was selected for and reared from mosquitoes captured in villages where permethrin treated bednets or curtains were being used. This colony was used to study the biochemical basis of permethrin resistance and its behavioural aspects. " All the mosquitoes from the villages where permethrin treated nets were present and the control villages speciated by PCR were found to be An. gambiae s.s Use of permethrin impregnated nets for one year, raised An. gambiae s.s permethrin tolerance (PT) to 2.5 times its' baseline value as measured by the WHO kit. In th-e second year of this studv, An. gambiae s.s permethrin tolerance showed no further significant rise in .comparison to the results of the first year. The results of the WHO cone test compared favourably with - those of the WHO kit with An.qembiee s.s from the bednet or curtain villages having a longer exposure time to 50 per cent mortality than mosquitoes from non intervention villages (10 minutes versus 5 minutes). Mosquitoes which were found to be tolerant to permethrin remained susceptible to other insecticides when tested in the WHO kit test. An.gambiae s.I. and An. funestus from Ahero were susceptible to all the insecticides they were tested against. All the An.gambiae s./ from Ahero which were speciated by normal taxonomic techniques using common visible features were found to be An. arabiensis. An. gambiae s.s. which were selected for resistance to permethrin had higher levels of mixed function oxidase (MFO) enzymes when compared to a susceptible strain. Resistance to permethrin in this colony was abolished by the use of piperonyl butoxide, which is a known oxidase inhibitor, and a permethrin synergist. Mosquitoes which were resistant to permethrin were more successful in feeding across a treated bennet (permethrin O.5gm/m2) compared to those which were susceptible. Most of the mosquitoes that were able to obtain a full blood meal across CI•• treated net successfully oviposited. It is concluded that village-wide use of permethrin impregnated nets can lead to selection for permethrin resistance in An. gambiae s.s. Those mosquitoes which were resistant to perrnetqrin were, however, not resistant to deltamethrin and propoxur. These insecticides can therefore be used as alternatives to permethrin in the event that permethrin resistance - compromises the efficacy of perrnethrin impregnated nets. Since the colony of An. gambiae s.s. selected for, resistance to perrnethrin was found to have higher levels of mixed function oxidases, the use of suitable synergists known to inhibit oxidase activity (such as piperonyl butoxide) can be used to forestall the development of oxidase related resistance. There was no further significant rise in permethrin tolerance in An. gambiaes.s. which were captured from villages where permethrin treated nets were present, during the second year of the study, in comparison to the rise in permethrin tolerance observed in the first year of the study. This could be attributed to immigration of susceptible mosquitoes from surrounding villages which had no treated nets, and also the presence of alternative blood meal sources such as cattle. These factors mini mise the selection for genes responsible for increased permethrin tolerance. It is also concluded that the WHO tube test and the WHO cone test can be easily used to monitor for the development of permethrin resistance in areas where permethrin impregnated nets are being used. Biochemical assays such as the oxidase microplate assay, can also be used to monitor for the development of. permethrin resistance in An. gambiae s.s. Some of the advantages of biochemical assays are that fewer numbers of mosquitoes are needed to perform the test and secondly, they can be carried out more rapidly than the conventional WHO assays. In the Ahero rice irrigation scheme, aqricultural pesticides are normally in use. The two main vectors of malaria; An. arabiensis and An. funestus were found to be all the major classes of insecticides. It would appear that the use of agricultural pesticides has not resulted in the development of resistance in the above vectors. The significance of these findings is discusseden
dc.titleEvaluation of physiological and behavioural resistance to permethrin and its cross-resistance spectrum in anopheles mosquitoes from Western Kenyaen
local.publisherSchool of Biological Sciences, University of Nairobien

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