Resting behaviour of malaria vectors in a highland and a lowland site of western Kenya: Implication on malaria vector control measures

Abstract

33Background: Understanding the interactions between increased insecticide resistance in field 34 malaria vector populations and the subsequent resting behaviour patterns is important for planning 35 adequate vector control measures in a specific context and sustaining the current vector 36 interventions. The aim of this study was to investigate the resting behavior, host preference and 37 infection with Plasmodium falciparum sporozoites by malaria vectors in different ecological 38 settings of western Kenya with different levels of insecticide resistance. 39 40 Methods: Indoor and outdoor resting Anopheline mosquitoes were sampled during the dry and 41 rainy seasons in Kisian (lowland site) and Bungoma (highland site), both in western Kenya. WHO 42 tube bioassay was used to determine levels of phenotypic resistance of first generation offspring 43 65 66 Conclusion: The study reports high densities of insecticide -resistant An. gambiae and An. funestus 67 resting indoors and the persistence of malaria transmission indoors with high entomological 68 inoculation rates (EIR) regardless of the use of Long-lasting insecticidal nets (LLINs). These 69 findings underline the difficulties of controlling malaria vectors resting and biting indoors using 70 the current interventions. Supplemental vector control tools and implementation of sustainable 71 insecticide resistance management strategies are needed in western Kenya.72 73 74 4 99Malaria vectors have been shown to adapt to changing environment due to either behavioural 100 avoidance or selection of mutations and recombination that favour their survival in the presence 101 of insecticides threatening the efficacy of the current indoor-based vector control tools [5,11] and 102 the resulting increase in residual transmission [12]. Insecticide resistance is common in sub- 103Saharan Africa with some regions reporting resistance to all classes of insecticides [13,14]. In 104 Kenya, the target site and metabolic resistance mechanisms play a major role in pyrethroid 105 resistance [15,16]. The primary malaria vectors in Kenya belong to An. gambiae complex and An. 106 funestus group due to their anthropophilic and endophilic behaviours that makes them be more 107 efficient in malaria transmission [17-19]. With the scale-up of indoor-based vector control tools 108 mosquitoes have changed behaviours; some are biting and resting indoors whilst others have 109 changed to prefer biting bite outdoors. Behavioral modifications including changes in biting time 110 and location [20-22], changes in host choice and shift from endophilic (i.e. resting in houses) to 111 exophilic (i.e. resting outdoors) behavior have been associated with long-term use of insecticide-112 based interventions [23,24]. Insecticide resistance could make mosquitoes respond numerically 113 and behaviorally to alter vector populations as well as resting and feeding behaviors. Knowledge 114 of the resting habits of resistant vectors and their feeding preference may predict the intensity of 115 malaria tran...

Current observations on shifts in malaria vector biting behavior and changing vulnerability to malaria transmission in contrasting ecosystems in Western Kenya

“…gambaie were responsible for malaria transmission both indoors and outdoors in the lowland and highland sites respectively, with majority of malaria infections occurring outdoors. The ndings are in agreement with previous studies that observed the two vectors to be the main drivers of malaria transmission in the region [25,26,29], however contrary to the present study, the early studies reported high infection rates indoors. It's worth mentioning that high bed net ownership and usage of > 90% was con rmed in all three sites.…”

“…In the highlands (Kimaeti), only An. gambiae was collected, with previous studies con rming the species to be dominant in the region [29,44]. This vector showed no change in biting activity as the results indicate that the species preferred feeding indoors with a pronounced activity late at night between 0100-0200 h. Historical studies have reported man to be the principal host for this species unlike its sibling species An.…”

“…The three malaria vectors are present in the highlands with An.gambiae and An. funestus being the dominant species depending on the season [28,29]. The highland and lowland sites of western Kenya have different levels of insecticide resistance (Owuor et al 2021).…”

Insecticide resistance status of indoor and outdoor resting malaria vectors in a highland and lowland site in Western Kenya

“…The malaria vector Anopheles arabiensis has been reported with increasing levels of kdr mutations [19]. There are no reports of kdr mutation at the locus 1014 in Anopheles funestus, also an important vector in Western Kenya and many parts of Africa despite having several reports of metabolic resistance [20][21][22]. The increasing levels of insecticide resistance in malaria mosquitoes have been associated with continuous exposure to insecticides in Long Lasting Insecticide Nets( LLINs) [23,24] and agro-chemicals such as pesticides due to the creation of selection pressures [25][26][27].…”

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“…The malaria vector Anopheles arabiensis has been reported with increasing levels of kdr mutations [19]. There are no reports of kdr mutation at the locus 1014 in Anopheles funestus, also an important vector in western Kenya and many parts of Africa despite having several reports of metabolic resistance [20][21][22]. The increasing levels of insecticide resistance in malaria mosquitoes is believed to be mainly caused by scaling up of insecticidal treated nets (ITNs) [23,24] and indiscriminate use of agro-chemicals for controlling crop pests in agriculture [25][26][27].…”