Biology subjects

Hien, D. F. d. S.

Publications and source records attributed to Hien, D. F. d. S..

6 recordsLinked to original sources

bioRxiv2024

Spatial and temporal characteristics of laboratory-induced Anopheles coluzzii swarms: shape, structure and flight kinematics

Anopheles mosquitoes mate at sunset in aerial swarms. The development of mating-based methods for effective malaria vector control requires a good knowledge of the flight behaviour of Anopheles species in mating swarms. However, the process of how swarms are formed and maintained remains poorly understood. Here, we characterized the three-dimensional spatial and temporal flight kinematics of Anopheles coluzzii males swarming above a ground marker. We observed that the location, shape and volume of swarms were highly stereotypic, consistent over the swarming duration, regardless of the number of individuals in the swarm. The swarm had an elliptical cone shape, and we observed a differential spatial distribution of flight kinematics parameters within the swarm volume. Among these parameters, only swarm density varied with swarm size. Using a sensory system-informed model, we show that swarm location and shape can accurately be modelled based on visual perception of the marker. To control swarm height, swarming individuals maintain an optical angle of the marker ranging from 24{degrees} to 55{degrees}. Limiting the viewing angle deviation to 4.5% of the maximum value results in the observed elliptical cone swarm shape. We discuss the implications of these finding in mating success, speciation and for vector control.

animal behavior and cognition↗

bioRxiv2024

Non-contact detection of pyrethroids widely used in vector control by Anopheles mosquitoes

Pyrethroids are the most widely used insecticides to control vector borne diseases including malaria. Physiological resistance mechanisms to these insecticides have been well described, whereas those for behavioral resistance remain overlooked. Field data suggest the presence of spatial sensory detection by Anopheles mosquitoes of the pyrethroid molecules used in insecticide-based control tools, such as long-lasting insecticide nets or insecticide residual spraying, opening the way to the emergence of a wide range of behavioral adaptations among malaria vectors. However, the spatial sensory detection of these molecules is controversial and needs to be demonstrated. The goal of this study was to behaviorally characterize the non-contact detection of three of the most common pyrethroids used for malaria vector control: permethrin, deltamethrin an -cypermethrin. To reach this goal, we recorded the behavior (takeoff response) of Anopheles gambiae pyrethroid-sensitive and resistant laboratory strains, as well as field collected mosquitoes from the Gambiae complex, when exposed to the headspace of bottles containing different doses of the insecticides at 25 and 35{degrees}C, in order to represent a range of laboratory and field temperatures. We found the proportion of laboratory susceptible and resistant female mosquitoes that took off was, in all treatments, dose and the temperature dependent. Sensitive mosquitoes were significantly more prone to take off only in the presence of -cypermethrin, whereas sensitive and resistant mosquitoes showed similar responses to permethrin and deltamethrin. Field-collected mosquitoes of the Gambiae complex were also responsive to permethrin, independently of the species identity (An. gambiae, An. coluzzi and An. arabiensis) or their genotypes for the kdr mutation, known to confer resistance to pyrethroids. The observed ability of Anopheles spp. mosquitoes to detect insecticides without contact could favor the evolution of behavioral modifications that may allow them to avoid or reduce the adverse effect of insecticides and thus, the development of behavioral resistance.

animal behavior and cognition↗

bioRxiv2023

Impact of blood meals taken on ivermectin-treated livestock on survival and fecundity of the malaria vector Anopheles coluzzii under laboratory conditions

Treatment of livestock with endectocides such as ivermectin is viewed as a complementary vector control approach to address residual transmission of malaria. However, efficacy of this treatment may vary between animal species. Hence, our purpose was to investigate the effects of ivermectin treatments of common livestock species on life history traits of the opportunistic malaria vector Anopheles coluzzii. Sheep, goats and pigs were treated using injectable veterinary ivermectin formulation at the species-specific doses (recommended dose for all species and high dose in pig). Mosquito batches were exposed to treated and control (not injected) animals at different days after treatment. Daily mosquito mortality was recorded and fecundity assessed through the count of gravid females and the number of eggs they developed. The recommended dose of ivermectin induced a significant decrease in mosquito survival for up to 7 days after injection (DAI), with a decrease of 89.7%, 66.7%, and 48.4% in treated pigs, goats and sheep, respectively, compared to control animals. In treated pigs, the triple therapeutic dose decreased mosquito survival of 68.97% relatively to controls up to 14 DAI. The average number in gravid females Anopheles that survived after feeding on treated animals were reduced when blood-meals were taken on sheep (2.57% and 42.03% at 2 and 7 DAI), or on goats (decrease of the 28.28% and 73.64% respectively at 2 and 7 DAI). This study shows that ivermectin treatments to animals negatively impacts An. coluzzii life history traits and could reduce vector densities in areas where livestock live near humans. However, due to short-term efficacy of single dose treatments, repeated treatments and potentially increased dosages would be required to span the transmission season. The use of long-acting ivermectin formulations is discussed as a mean for extending efficacy while remaining cost effective.

systems biology↗

bioRxiv2023

Mosquito aging modulates the development, virulence and transmission potential of pathogens

Host age variation is a striking source of heterogeneity that can shape the evolution and transmission dynamic of pathogens. Compared to vertebrate systems, our understanding of the impact of host age on invertebrate-pathogen interactions remains limited. We examined the influence of mosquito age on key life-history traits driving human malaria transmission. Females of Anopheles coluzzii, a major malaria vector, belonging to three age classes (4, 8, and 12 day-old), were experimentally infected with Plasmodium falciparum field isolates. Our findings revealed reduced competence in 12-day-old mosquitoes, characterized by lower oocyst/sporozoite rates and intensities compared to younger mosquitoes. Despite shorter median longevities in older age classes, infected 12-day-old mosquitoes exhibited improved survival, suggesting that the infection might act as a fountain of youth for older mosquitoes specifically. The timing of sporozoite appearance in the salivary glands remained consistent across mosquito age classes, with an extrinsic incubation period of approximately 13 days. Integrating these results into an epidemiological model revealed a lower vectorial capacity for older mosquitoes compared to younger ones, albeit still substantial due to extended longevity in the presence of infection. Considering age heterogeneity provides valuable insights for ecological and epidemiological studies, informing targeted control strategies to mitigate pathogen transmission.

ecology↗

bioRxiv2022

Intervention reducing malaria parasite load in vector mosquitoes: no impact on Plasmodium falciparum extrinsic incubation period and the survival of Anopheles gambiae

In the fight against malaria, transmission blocking interventions (TBIs) are promising approaches to complement conventional tools. They aim to prevent the infection of the vectors and thereby reduce the subsequent exposure of a human population to infectious mosquitoes. The effectiveness of these approaches has been shown to depend on the initial intensity of infection in mosquitoes, often measured as the mean number of oocysts resulting from an infectious blood meal prior to intervention. In mosquitoes exposed to a high infection load, current TBI candidates are expected to be ineffective at completely blocking infection but will decrease parasite load and therefore, potentially also affect key parameters of vector transmission. The present study aims to investigate the consequences of changes in oocyst intensity on downstream parasite development and mosquito survival. To address this, we experimentally produced different infection intensities in Anopheles gambiae females by diluting gametocytes from natural Plasmodium falciparum isolates and used a newly developed non-destructive method based on the exploitation of mosquito sugar feeding to track parasite and mosquito life history traits throughout sporogonic development. Our results indicate that P. falciparum extrinsic incubation period (EIP) and mosquito survival did not vary with parasite density but differed significantly between parasite isolates. Our results do not identify here unintended consequences of the decrease of parasite loads in mosquitoes on the parasite incubation period or on mosquito survival, two key parameters of vectorial capacity, and hence support the transmission blocking strategies to control malaria. Author summaryIn the fight against malaria, it is recognized that the use of several complementary strategies is necessary to significantly reduce transmission and improve human health. Among these, transmission blocking strategies aim at blocking the development of the parasites within the mosquito vectors. This approach should prevent infection in most of mosquitoes feeding on infectious hosts and thus block the transmission. However, in some cases it may only reduce parasite load without fully clearing the infection. Here we identified potential risks: if reducing parasite load would reduce the incubation period of the parasite in the mosquitoes or increase the longevity of the mosquitoes, undesirable consequences may occur with an increased efficiency of these mosquitoes to transmit parasites to human. We therefore tested these hypotheses and experimentally produced different infection loads in vector mosquitoes Anopheles gambiae by using dilutions of Plasmodium falciparum isolates from naturally infected human donors. We observed that the longevity of the mosquitoes and the incubation period of the parasites were not affected by the parasite load. This is not consistent with the unintended risks that we investigated and thus strengthens the potential of transmission blocking interventions in the toolbox to combat malaria.

evolutionary biology↗

bioRxiv2019

Anopheles bionomic, insecticide resistance and malaria transmission in southwest Burkina Faso: a pre-intervention study

BackgroundThe present study presents results of entomological surveys conducted to address the malaria vectors bionomic, insecticide resistance and transmission prior to the implementation of new strategies complement long-lasting insecticidal nets (LLINs) in the framework of a randomized control trial in southwest Burkina Faso. MethodsWe conducted entomological surveys in 27 villages during the dry cold season (January 2017), dry hot season (March 2017) and rainy season (June 2017). We carried out hourly catches (from 17:00 to 09:00) inside and outside 4 houses in each village using the Human Landing Catch technique. Mosquitoes were identified using morphological taxonomic keys. Specimens belonging to the Anopheles gambiae complex and Funestus Group were identified using molecular techniques as well as detection of Plasmodium falciparum infection and insecticide resistance target-site mutations. ResultsEight Anopheles species were detected in the area. Anopheles funestus s.s was the main vector during the dry cold season. It was replaced by Anopheles coluzzii during the dry hot season whereas An. coluzzii and An. gambiae s.s. were the dominant species during the rainy season. Species composition of the Anopheles population varied significantly among surveys. All researched target site mutation of insecticide resistance (kdr-w, kdr-e and ace-1) were detected in all members of the An. gambiae complex of the area but at different frequencies. We observed early and late biting phenotypes in the main malaria vector species. Entomological inoculation rates were 0.087, 0.089 and 0.375 infected bites per human per night during dry cold season, dry hot season and rainy season, respectively. ConclusionThe intensity of malaria transmission was high despite the universal coverage with LLINs. We detected early and late biting phenotypes in the main malaria vector species as well as physiological insecticide resistance mechanisms. These vectors might mediate residual transmission. These data highlight the need to develop complementary tools in addition to LLINs in order to better control resistant malaria vectors and to monitor insecticide resistance.

epidemiology↗