College of Health Sciences

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Browsing College of Health Sciences by Author "Asoala, Victor"

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    Malaria transmission dynamics and insecticide resistance of malaria vectors in the Kassena-Nankana Districts of Ghana
    (KNUST, 2016-02) Asoala, Victor
    ABSTRACT Plasmodium falciparum malaria is a serious tropical disease that causes more than one million deaths each year, mostly in Africa. It is transmitted by a range of Anopheles mosquitoes. Progress in global malaria control over the past decade is largely gained through investments in vector control; especially insecticide treated mosquito nets (ITNs). ITNs have been used extensively in the Kassena Nankana districts (KND) of Ghana for over two decades. This study aimed to investigate the intensity of malaria transmission and resistance status of vector populations in KND, relate these data to historical patterns of transmission intensity and determine whether the presence of insecticide resistance has an effect on malaria transmission in KND. Anopheles gambiae s.l. was the predominant Anopheles which constituted 68.82% (95% CI 68.18 - 69.45) (N=13938). Anopheles funestus constituted 10.97% (95% CI 10.55 – 11.41) (N=2222) whilst An. pharoensis and An. rufipes constituted the rest of 20. 21% (95% CI 19.66 - 20.77), (N=4092). Molecular analysis of the An. gambiae s.l. revealed only An. gambiae s.s. as sibling species, mainly of Anopheles coluzzii (M-form). Anopheles biting started early, peaked around 10.00pm and continued to the early hours of the morning. Plasmodium falciparum sporozoite infectivity results revealed active transmission by An. gambiae s.s.as early as 8pm and serious transmission occurred towards the early hours of the morning because of combined infective biting by both An. gambiae s.s and An. funestus. There was marked temporal variations in malaria intensity estimated as the entomological inoculation rate (EIR) with the irrigated zone experiencing the highest during the year. Compared to what was reported over a decade ago, the intensity of transmission has reduced by 66.7% from 418 to 139 infective bites/man/year. Results of the study indicated high phenotypic resistance to the insecticide classes tested. High frequencies of the Knock down resistance (kdr) and vi Ace-1R alleles (responsible for pyretroid/DDT and carbamate /organophosphate resistance respectively) including the N1575Y allele (reported to enhance resistance to pyrethroids) was observed. The variations observed in biting patterns, transmission intensity and the high insecticide resistance observed in the main malaria vector has important consequences for the success of the widely used insecticide-based strategies in KND.