Emergence of behavioural avoidance strategies of malaria vectors in areas of high LLIN coverage in Tanzania

Abstract

Despite significant reductions in malaria transmission across Africa since 2000, progress is stalling. this has been attributed to the development of insecticide resistance and behavioural adaptations in malaria vectors. Whilst insecticide resistance has been widely investigated, there is poorer understanding of the emergence, dynamics and impact of mosquito behavioural adaptations. We conducted a longitudinal investigation of malaria vector host choice over 3 years and resting behaviour over 4 years following a mass long-lasting insecticidal nets (LLINs) distribution in Tanzania. By pairing observations of mosquito ecology with environmental monitoring, we quantified longitudinal shifts in host-choice and resting behaviour that are consistent with adaptation to evade LLins. the density of An. funestus s.l., declined significantly through time. In tandem, An. arabiensis and An. funestus s.l. exhibited an increased rate of outdoor relative to indoor resting; with An. arabiensis reducing the proportion of blood meals taken from humans in favour of cattle. By accounting for environmental variation, this study detected clear evidence of intra-specific shifts in mosquito behaviour that could be obscured in shorter-term or temporally-coarse surveys. This highlights the importance of mosquito behavioural adaptations to vector control, and the value of longer-term behavioural studies. Malaria remains a major public health concern in Africa despite a vast reduction in cases and deaths over the last decade 1, 2. Malaria parasites (Plasmodium sp.) are transmitted by Anopheles mosquitoes, with the primary vectors in Africa belonging to the Anopheles gambiae s.l. species complex and Anopheles funestus group 3. Vector control, primarily using long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), remains the primary strategy for reducing malaria transmission. Both these strategies rely on exploitation of the behavioural predisposition of many African vector species to feed on humans (anthrophagy) and rest inside houses (endophily) 4. These interventions have generated substantial declines in malaria prevalence in many African settings 1 , including the near eradication of highly anthropophagic and endophilic vector species in some areas 5-7. Residual malaria transmission persists even where LLIN and IRS coverage is high 8, 9 due to a combination of biological, social and health systems factors; with adaptive changes occurring in vector populations likely playing a major role. There has been widespread development of physiological insecticide resistance (IR) in vectors 10, 11. Additionally, vectors may adapt their behaviour to minimize contact with insecticides in houses by, for example, biting people before they go to bed, biting and resting outdoors, or switching to feed on livestock instead of humans 12-15. While IR has been extensively investigated and widely documented 16 , there is poorer

Mosquito Trilogy: Microbiota, Immunity and Pathogens, and Their Implications for the Control of Disease Transmission

“…For example, massive use of LLINs (longlasting insecticidal nets, ITN with longer duration of effectiveness due to the incorporation of the insecticide into fibers during the manufacturing process) has greatly contributed to combat malaria (Carnevale and Gay, 2019). However, the efficacy of these control measures is hampered by the selection and spread of resistance (Hemingway, 2018), which is a complex phenomenon that accounts for modifications of multiple biochemical processes in mosquitoes (Hemingway, 2018;Ingham et al, 2020) or, also, for alterations of the mosquito biting behavior (e.g., shifts from an indoor-to an out-door host-seeking behavior) (Moiroux et al, 2012;Kreppel et al, 2020;Perugini et al, 2020). The massive use of insecticides raises also concerns, in relation to the impact on non-target species and the environment (Mansouri et al, 2017).…”

Is Outdoor-Resting Behaviour in Malaria Vectors Consistent? Short Report From Northern Ghana.

“…However, recent reports are indicating that vector control tools are inducing behavioural changes in mosquitoes such that some vector species have shifted from indoor-resting behaviour to resting outdoors (exophilic). This was as documented from studies in Ethiopia [5], Ghana [6,7], Kenya [8,9)], Libreville [10] and Tanzania [11,12]. Such behavioural diversi cation in vector population can be detrimental to vector control [13,14], which mainly target vectors resting indoors.…”

Modelling Sand Fly Lutzomyia longipalpis Attraction to Host Odour: Synthetic Sex-Aggregation Pheromone Dominates the Response

“…Understanding the blood-seeking behaviour of arthropod vectors has relevance to vector control against transmission of public and veterinary health diseases [ 1 , 2 ]. The emerging behavioural adaptations of important mosquito vectors to alter their blood-feeding host preferences, locations and feeding time periods, and thus their ability to evade fatal exposure to indoor insecticide interventions [ 2 , 3 , 4 ], highlight the need for sustained vector surveillance and development of complimentary vector control strategies.…”