Modelling the risk of being bitten by malaria vectors in a vector control area in southern Benin, west Africa

Abstract Background Odour-based tools targeting gravid malaria vectors may complement existing intervention strategies. Anopheles arabiensis are attracted to, and stimulated to oviposit by, natural and synthetic odours of wild and domesticated grasses associated with mosquito breeding sites. While such synthetic odour lures may be used for vector control, these may have limited efficacy when placed in direct competition with the natural source. In this study, workflows developed for plant-feeding pests was used to design and evaluate a chimeric odour blend based on shared attractive compounds found in domesticated grass odours. Methods Variants of a synthetic odour blend, composed of shared bioactive compounds previously identified in domesticated grasses, was evaluated sequentially in a two-choice olfactometer to identify a ratio-optimized attractive blend for malaria vectors. During this process, blends with ratios that were significantly more attractive than the previously identified synthetic rice blend were compared to determine which was most attractive in the two-choice olfactometer. To determine whether all volatile components of the most attractive blend were necessary for maximal attraction, subtractive assays were then conducted, in which individual components were removed for the most attractive blend, to define the final composition of the chimeric blend. Binary logistic regression models were used to determine significance in all two-choice assays. The chimeric blend was then assessed under field conditions in malaria endemic villages in Ethiopia, to assess the effect of dose, trap type, and placement relative to ground level. Field data were analyzed both descriptively and using a Welch-corrected t-test. Results A ratio-optimized chimeric blend was identified that significantly attracted gravid An. arabiensis under laboratory conditions. In the field, trap captures of An. arabiensis and Anopheles pharoensis were dependent on the presence of the lure, trap type (CDC, BG Sentinel and Suna traps), placement relevant to ground level, with low release rates generally luring more mosquitoes. Conclusions The workflow designed for the development of chimeric lures provides an innovative strategy to target odour-mediated behaviours. The chimeric lure identified here can be used in existing trapping systems, and be customized to increase sustainability, in line with goals of the Global Vector Control Response Group.

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Malaria vector species composition and entomological indices following indoor residual spraying in regions bordering Lake Victoria, Tanzania

Malaria Journal ◽

10.1186/s12936-020-03452-w ◽

2020 ◽

Vol 19 (1) ◽

Author(s):

Charles Kakilla ◽

Alphaxard Manjurano ◽

Karen Nelwin ◽

Jackline Martin ◽

Fabian Mashauri ◽

...

Keyword(s):

Species Composition ◽

Vector Control ◽

Malaria Vector ◽

Lake Victoria ◽

Indoor Residual Spraying ◽

Transmission Risk ◽

Malaria Vectors ◽

Vector Species ◽

Sporozoite Rate ◽

Pirimiphos Methyl

Abstract Background Vector control through long-lasting insecticidal nets (LLINs) and focal indoor residual spraying (IRS) is a major component of the Tanzania national malaria control strategy. In mainland Tanzania, IRS has been conducted annually around Lake Victoria basin since 2007. Due to pyrethroid resistance in malaria vectors, use of pyrethroids for IRS was phased out and from 2014 to 2017 pirimiphos-methyl (Actellic® 300CS) was sprayed in regions of Kagera, Geita, Mwanza, and Mara. Entomological surveillance was conducted in 10 sprayed and 4 unsprayed sites to determine the impact of IRS on entomological indices related to malaria transmission risk. Methods WHO cone bioassays were conducted monthly on interior house walls to determine residual efficacy of pirimiphos-methyl CS. Indoor CDC light traps with or without bottle rotator were hung next to protected sleepers indoors and also set outdoors (unbaited) as a proxy measure for indoor and outdoor biting rate and time of biting. Prokopack aspirators were used indoors to capture resting malaria vectors. A sub-sample of Anopheles was tested by PCR to determine species identity and ELISA for sporozoite rate. Results Annual IRS with Actellic® 300CS from 2015 to 2017 was effective on sprayed walls for a mean of 7 months in cone bioassay. PCR of 2016 and 2017 samples showed vector populations were predominantly Anopheles arabiensis (58.1%, n = 4,403 IRS sites, 58%, n = 2,441 unsprayed sites). There was a greater proportion of Anopheles funestus sensu stricto in unsprayed sites (20.4%, n = 858) than in sprayed sites (7.9%, n = 595) and fewer Anopheles parensis (2%, n = 85 unsprayed, 7.8%, n = 591 sprayed). Biting peaks of Anopheles gambiae sensu lato (s.l.) followed periods of rainfall occurring between October and April, but were generally lower in sprayed sites than unsprayed. In most sprayed sites, An. gambiae s.l. indoor densities increased between January and February, i.e., 10–12 months after IRS. The predominant species An. arabiensis had a sporozoite rate in 2017 of 2.0% (95% CI 1.4–2.9) in unsprayed sites compared to 0.8% (95% CI 0.5–1.3) in sprayed sites (p = 0.003). Sporozoite rates were also lower for An. funestus collected in sprayed sites. Conclusion This study contributes to the understanding of malaria vector species composition, behaviour and transmission risk following IRS around Lake Victoria and can be used to guide malaria vector control strategies in Tanzania.

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Human biting rhythm of Anopheles gambiae Giles, 1902 (Diptera: Culicidae) and sleeping behaviour of pregnant women in a lagoon area in Southern Benin

BMC Research Notes ◽

10.1186/s13104-021-05615-7 ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Armel Djènontin ◽

Aziz Bouraima ◽

Christophe Soares ◽

Seun Egbinola ◽

Gilles Cottrell

Keyword(s):

Plasmodium Falciparum ◽

Pregnant Women ◽

Anopheles Gambiae ◽

Early Morning ◽

Allelic Frequency ◽

Malaria Vectors ◽

Mosquito Nets ◽

Anopheles Gambiae Giles ◽

Almost All ◽

Southern Benin

Abstract Objective In the framework of EVALMOUS study aiming to assess the use and effectiveness of mosquito nets by pregnant women and other members of their household in a lagoon area in southern Benin, the behaviour of pregnant women relative to the time they go to bed using the net were recorded. Malaria vectors biting rhythm, Plasmodium falciparum infection and insecticide resistance genes in malaria vectors were also determined. Results Overall, 3848 females of Anopheles gambiae s. l were collected and 280 pregnant women responded to the survey. Almost all Anopheles gambiae s. l. tested were Anopheles coluzzi Coetzee and Wilkerson 2013 (Diptera: Culicidae). The CSP index in malaria vector was 1.85% and the allelic frequency of kdr gene was 74.4%. Around 90% of bites and Plasmodium falciparum Welch, 1897 (Haemosporida: Plasmodiidae) transmission occurred between 10 p.m. and 6 a.m., which coincides with the period when more than 80% of pregnant women were under bednet. Despite a slight early evening and early morning biting activity of malaria vectors in the study area, the good use of nets might remain a useful protection tool against mosquito biting and malaria transmission.

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Insecticide resistance status of Anopheles arabiensis in irrigated and non-irrigated areas in western Kenya

Parasites & Vectors ◽

10.1186/s13071-021-04833-z ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Pauline Winnie Orondo ◽

Steven G. Nyanjom ◽

Harrysone Atieli ◽

John Githure ◽

Benyl M. Ondeto ◽

...

Keyword(s):

Insecticide Resistance ◽

Vector Control ◽

Anopheles Arabiensis ◽

Crop Protection ◽

Indoor Residual Spraying ◽

Malaria Vectors ◽

Western Kenya ◽

Animal Protection ◽

Selection Of ◽

Selection Of Resistance

Abstract Background Malaria control in Kenya is based on case management and vector control using long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). However, the development of insecticide resistance compromises the effectiveness of insecticide-based vector control programs. The use of pesticides for agricultural purposes has been implicated as one of the sources driving the selection of resistance. The current study was undertaken to assess the status and mechanism of insecticide resistance in malaria vectors in irrigated and non-irrigated areas with varying agrochemical use in western Kenya. Methods The study was carried out in 2018–2019 in Homa Bay County, western Kenya. The bioassay was performed on adults reared from larvae collected from irrigated and non-irrigated fields in order to assess the susceptibility of malaria vectors to different classes of insecticides following the standard WHO guidelines. Characterization of knockdown resistance (kdr) and acetylcholinesterase-inhibiting enzyme/angiotensin-converting enzyme (Ace-1) mutations within Anopheles gambiae s.l. species was performed using the polymerase chain reaction (PCR) method. To determine the agricultural and public health insecticide usage pattern, a questionnaire was administered to farmers, households, and veterinary officers in the study area. Results Anopheles arabiensis was the predominant species in the irrigated (100%, n = 154) area and the dominant species in the non-irrigated areas (97.5%, n = 162), the rest being An. gambiae sensu stricto. In 2018, Anopheles arabiensis in the irrigated region were susceptible to all insecticides tested, while in the non-irrigated region reduced mortality was observed (84%) against deltamethrin. In 2019, phenotypic mortality was decreased (97.8–84% to 83.3–78.2%). In contrast, high mortality from malathion (100%), DDT (98.98%), and piperonyl butoxide (PBO)-deltamethrin (100%) was observed. Molecular analysis of the vectors from the irrigated and non-irrigated areas revealed low levels of leucine-serine/phenylalanine substitution at position 1014 (L1014S/L1014F), with mutation frequencies of 1–16%, and low-frequency mutation in the Ace-1R gene (0.7%). In addition to very high coverage of LLINs impregnated with pyrethroids and IRS with organophosphate insecticides, pyrethroids were the predominant chemical class of pesticides used for crop and animal protection. Conclusion Anopheles arabiensis from irrigated areas showed increased phenotypic resistance, and the intensive use of pesticides for crop protection in this region may have contributed to the selection of resistance genes observed. The susceptibility of these malaria vectors to organophosphates and PBO synergists in pyrethroids offers a promising future for IRS and insecticide-treated net-based vector control interventions. These findings emphasize the need for integrated vector control strategies, with particular attention to agricultural practices to mitigate mosquito resistance to insecticides. Graphic abstract

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Swampy area transformations by exploitation ofRaphia hookeri (Arecaceae) in southern Benin (West Africa)

Human Ecology ◽

10.1007/bf01262028 ◽

1988 ◽

Vol 16 (1) ◽

pp. 87-94 ◽

Cited By ~ 2

Author(s):

Jean -Pierre Profizi

Keyword(s):

West Africa ◽

Southern Benin

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Three-dimensional modelling of a coastal sedimentary basin of southern Benin (West Africa)

IAH - Selected Papers on Hydrogeology - Applied Groundwater Studies in Africa ◽

10.1201/9780203889497.ch26 ◽

2008 ◽

Author(s):

F Azonsi ◽

M Boukari ◽

P Viaene

Keyword(s):

West Africa ◽

Sedimentary Basin ◽

Three Dimensional ◽

Southern Benin

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The impact of transfluthrin on the spatial repellency of the primary malaria mosquito vectors in Vietnam: Anopheles dirus and Anopheles minimus

Malaria Journal ◽

10.1186/s12936-019-3092-4 ◽

2020 ◽

Vol 19 (1) ◽

Cited By ~ 1

Author(s):

Nicholas J. Martin ◽

Vu S. Nam ◽

Andrew A. Lover ◽

Tran V. Phong ◽

Tran C. Tu ◽

...

Keyword(s):

Vector Control ◽

Large Scale ◽

Limit Of Detection ◽

Malaria Vectors ◽

Adult Mosquito ◽

Anopheles Dirus ◽

Anopheles Minimus ◽

Control Programmes ◽

The Impact ◽

Spatial Repellency

Abstract Background The complexity of mosquito-borne diseases poses a major challenge to global health efforts to mitigate their impact on people residing in sub-tropical and tropical regions, to travellers and deployed military personnel. To supplement drug- and vaccine-based disease control programmes, other strategies are urgently needed, including the direct control of disease vectors. Modern vector control research generally focuses on identifying novel active ingredients and/or innovative methods to reduce human-mosquito interactions. These efforts include the evaluation of spatial repellents, which are compounds capable of altering mosquito feeding behaviour without direct contact with the chemical source. Methods This project examined the impact of airborne transfluthrin from impregnated textile materials on two important malaria vectors, Anopheles dirus and Anopheles minimus. Repellency was measured by movement within taxis cages within a semi-field environment at the National Institute of Hygiene and Epidemiology in Hanoi, Vietnam. Knockdown and mortality were measured in adult mosquito bioassay cages. Metered-volume air samples were collected at a sub-set of points in the mosquito exposure trial. Results Significant differences in knockdown/mortality were observed along a gradient from the exposure source with higher rates of knockdown/mortality at 2 m and 4 m when compared with the furthest distance (16 m). Knockdown/mortality was also greater at floor level and 1.5 m when compared to 3 m above the floor. Repellency was not significantly different except when comparing 2 m and 16 m taxis cages. Importantly, the two species reacted differently to transfluthrin, with An. minimus being more susceptible to knockdown and mortality. The measured concentrations of airborne transfluthrin ranged from below the limit of detection to 1.32 ng/L, however there were a limited number of evaluable samples complicating interpretation of these results. Conclusions This study, measuring repellency, knockdown and mortality in two malaria vectors in Vietnam demonstrates that both species are sensitive to airborne transfluthrin. The differences in magnitude of response between the two species requires further study before use in large-scale vector control programmes to delineate how spatial repellency would impact the development of insecticide resistance and the disruption of biting behaviour.

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Community Knowledge, Perceptions, And Practices Regarding Malaria and Its Control In Jabi Tehnan District, Amhara Region, Northwest Ethiopia

10.21203/rs.3.rs-489446/v1 ◽

2021 ◽

Author(s):

Abebe Asale ◽

Zewdu Abro ◽

Bayu Enchalew ◽

Alayu Tesager ◽

Aklilu Belay ◽

...

Keyword(s):

Vector Control ◽

Malaria Control ◽

Community Education ◽

Indoor Residual Spraying ◽

Community Empowerment ◽

Malaria Episode ◽

Malaria Vectors ◽

Bed Nets ◽

Health Seeking ◽

Malaria Parasites

Abstract Background: Key program components of malaria control in Ethiopia include community empowerment and mobilization, vector control using long-lasting insecticidal nets (LLINs), indoor residual spraying (IRS), prompt diagnosis and treatment, and disease surveillance. However, the effectiveness of these interventions is often undermined by various challenges, including insecticide and drug resistance, the plasticity of malaria vectors feeding and biting behavior, and certain household factors that lead to misuse and poor utilization of LLINs. The primary objective of this study was to document households’ perceptions towards malaria and assess the prevalence of the disease and the constraints related to the ongoing interventions in Ethiopia (LLINs, IRS, community mobilization house screening). Method: The study was conducted in Jabi Tehnan district, Northwestern Ethiopi,a from November 2019 to March 2020. A total of 3,010 households distributed over 38 kebeles (villages) were randomly selected for socio-economic and demographic survey. Focus group discussions (FGDs) were conducted in 11 different health clusters taking into account agro-ecological differences. A total of 1,256 children under 10 years of age were screened for malaria parasites using microscopy in order to determine malaria prevalence. Furthermore, five-year malaria trend analysis was undertaken based on data obtained from the district health office to understand the disease dynamics.Result: Malaria knowledge in the area was high as all FGD participants correctly identified mosquito bites during the night as sources of malaria transmission. Delayed health seeking behavior remains a key behavioral challenge in malaria control as it took patients on average 4 days before reporting the case at the nearby health facility. On average households lost 2.53 working days per person-per malaria episode and theey spent US$ 18 per person perepisode. Out of the 1,256 randomly selected under 10 children tested for malaria parasites, 11 (0.89%) were found to be positive. Malaria disproportionately affected the adult segment of the population more, 50% of the total cases reported from households whose age was 15 and beyond. The second most affected group was the age group between 5 and 14 years followed by children under 10, with 31% and 14% burden,respectively.Conclusion: Despite the achievement of universal coverage in terms of LLINs access, utilization of vector control interventions in the area remained low.Using bed nets for unintended purposes remained a major challenge. Therefore, continued community education and communication work should be prioritised in the study area to bring about the desired behavioral changes.

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Indoor use of attractive toxic sugar bait (ATSB) to effectively control malaria vectors in Mali, West Africa

Malaria Journal ◽

10.1186/s12936-015-0819-8 ◽

2015 ◽

Vol 14 (1) ◽

Cited By ~ 40

Author(s):

Whitney A Qualls ◽

Günter C Müller ◽

Sekou F Traore ◽

Mohamed M Traore ◽

Kristopher L Arheart ◽

...

Keyword(s):

West Africa ◽

Malaria Vectors

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