The impact of bund construction on the transmission of malaria in The Gambia

Water impoundments are known to affect the risk of many vector-borne diseases. Here I examine the impact of bund (small embanlonents) construction on the transmission of malaria in The Gambia. I hypothesised that bund construction, designed to collect rainwater for irrigation and keeping saltwater out, would provide ideal breeding sites for Anopheles gambiae mosquitoes, the major vectors of malaria in Africa, and thereby increase malaria transmission. Mosquito larvae were sampled along transects in three different areas. Each transect lay perpendicular to a bund, including an area 100m either side of the bund. These were sampled for larvae using area samplers every three weeks from May to December 2005, including the period of annual rainfall from June to October. Adult mosquitoes were caught using three emergence traps which were positioned at each side of the bund in different water bodies (i.e. six at each transect, three either side of the bunds), within 50m left and right of each transect. During a Countrywide survey, 20 transects were sampled in different parts of The Gambia in September 2005, when mosquito numbers were relatively high. 10 were situated in parts of the river where it was salt and 10 were situated in parts of the river where the water was fresh. Mosquitoes were roughly twice as common in water on the landward side of the bunds, 68% of Anopheles larvae and 84% of all mosquito larvae, (OR) = 9.37, 95% confidence intervals (95% CIs = 2.26-38.79, P <0.002), compared with the riverside. Similarly 82% of Anophelme adults and 89% of all adult mosquitoes (OR = 2.59, 95% CIs = 1.23-5.48, Р - 0.013) were collected on the landward side. There is also an indication that this is also true for the countrywide survey in which more mosquitoes were collected from the landside of the bund (63% Anophelines, 65% Culicines), although this did not reach statistical significance. One possible explanation for these findings is that larvae on the riverside of the bunds are washed away with the tide and predated by the larger number of fish found there; These findings indicate that the construction of bunds for agricultural purposes increases mosquito larval density on the landward side by increasing the breeding ground for malaria vectors of the An. Gambiae complex. These constructions increase the number of vector mosquitoes emerging from the floodplains of the River Gambia, and thus are likely to increase the intensity of malaria transmission

Status of insecticide resistance in Anopheles gambiae (s.l.) of The Gambia.

BACKGROUND: Vector control activities, namely long-lasting insecticidal nets (LLIN) and indoor residual spraying (IRS), have contributed significantly to the decreasing malaria burden observed in The Gambia since 2008. Nevertheless, insecticide resistance may threaten such success; it is important to regularly assess the susceptibility of local malaria vectors to available insecticides. METHODS: In the transmission seasons of 2016 and 2017, Anopheles gambiae (s.l.) larvae were sampled in or around the nine vector surveillance sentinel sites of the Gambia National Malaria Control Programme (GNMCP) and in a few additional sampling points. Using WHO susceptibility bioassays, female adult mosquitoes were exposed to insecticide-impregnated papers. Molecular identification of sibling species and insecticide resistance molecular markers was done on a subset of 2000 female mosquitoes. RESULTS: A total of 4666 wild-caught female adult mosquitoes were exposed to either permethrin (n = 665), deltamethrin (n = 744), DDT (n = 1021), bendiocarb (n = 990) or pirimiphos-methyl (n = 630) insecticide-impregnated papers and control papers (n = 616). Among the 2000 anophelines, 1511 (80.7%) were Anopheles arabiensis, 204 (10.9%) Anopheles coluzzii, 75 (4%) Anopheles gambiae (s.s.), and 83 (4.4%) An. gambiae (s.s.) and An. coluzzii hybrids. There was a significant variation in the composition and species distribution by regions and year, P = 0.009. Deltamethrin, permethrin and DDT resistance was found in An. arabiensis, especially in the coastal region, and was mediated by Vgsc-1014F/S mutations (odds ratio = 34, P = 0.014). There was suspected resistance to pirimiphos-methyl (actellic 300CS) in the North Bank Region although only one survivor had the Ace-1-119S mutation. CONCLUSIONS: As no confirmed resistance to bendiocarb and actellic 300CS was detected, the national malaria control programme can continue using these insecticides for IRS. Nevertheless, the detection of Ace-1 119S mutation warrants extensive monitoring. The source of insecticide pressure driving insecticide resistance to pyrethroids and DDT detected at the coastal region should be further investigated in order to properly manage the spread of resistance in The Gambia

Mass Drug Administration With High-Dose Ivermectin and Dihydroartemisinin-Piperaquine for Malaria Elimination in an Area of Low Transmission With High Coverage of Malaria Control Interventions: Protocol for the MASSIV Cluster Randomized Clinical Trial

Background: With a decline in malaria burden, innovative interventions and tools are required to reduce malaria transmission further. Mass drug administration (MDA) of artemisinin-based combination therapy (ACT) has been identified as a potential tool to further reduce malaria transmission, where coverage of vector control interventions is already high. However, the impact is limited in time. Combining an ACT with an endectocide treatment that is able to reduce vector survival, such as ivermectin (IVM), could increase the impact of MDA and offer a new tool to reduce malaria transmission. Objective: The study objective is to evaluate the impact of MDA with IVM plus dihydroartemisinin-piperaquine (DP) on malaria transmission in an area with high coverage of malaria control interventions. Methods: The study is a cluster randomized trial in the Upper River Region of The Gambia and included 32 villages (16 control and 16 intervention). A buffer zone of ~2 km was created around all intervention clusters. MDA with IVM plus DP was implemented in all intervention villages and the buffer zones; control villages received standard malaria interventions according to the Gambian National Malaria Control Program plans. Results: The MDA campaigns were carried out from August to October 2018 for the first year and from July to September 2019 for the second year. Statistical analysis will commence once the database is completed, cleaned, and locked. Conclusions: This is the first cluster randomized clinical trial of MDA with IVM plus DP. The results will provide evidence on the impact of MDA with IVM plus DP on malaria transmission. Trial Registration: ClinicalTrials.gov NCT03576313; https://clinicaltrials.gov/ct2/show/NCT03576313 International Registered Report Identifier (IRRID): DERR1-10.2196/2090

Building the capacity of West African countries in Aedes surveillance: inaugural meeting of the West African Aedes Surveillance Network (WAASuN)

Arboviral diseases such as dengue, Zika and chikungunya transmitted by Aedes mosquitoes have been reported in 34 African countries. Available data indicate that in recent years there have been dengue and chikungunya outbreaks in the West Africa subregion, in countries including Côte d’Ivoire, Burkina Faso, Gabon, Senegal, and Benin. These viral diseases are causing an increased public health burden, which impedes poverty reduction and sustainable development. Aedes surveillance and control capacity, which are key to reducing the prevalence of arboviral infections, need to be strengthened in West Africa, to provide information essential for the formulation of effective vector control strategies and the prediction of arboviral disease outbreaks. In line with these objectives, the West African Aedes Surveillance Network (WAASuN) was created in 2017 at a meeting held in Sierra Leone comprising African scientists working on Aedes mosquitoes. This manuscript describes the proceedings and discusses key highlights of the meeting

Hand application of corn granule in highly vegetated areas of the floodplains

<p><b>Copyright information:</b></p><p>Taken from "Microbial larvicides for malaria control in The Gambia"</p><p>http://www.malariajournal.com/content/6/1/76</p><p>Malaria Journal 2007;6():76-76.</p><p>Published online 7 Jun 2007</p><p>PMCID:PMC1899511.</p><p></p

Liquid application of microbial larvicides with 15 litres capacity knapsack sprayers on open water surface (edge of floodwater)

<p><b>Copyright information:</b></p><p>Taken from "Microbial larvicides for malaria control in The Gambia"</p><p>http://www.malariajournal.com/content/6/1/76</p><p>Malaria Journal 2007;6():76-76.</p><p>Published online 7 Jun 2007</p><p>PMCID:PMC1899511.</p><p></p

Multi-country review of ITN routine distribution data: are ANC and EPI channels achieving their potential?

Abstract Background Routine continuous distribution (CD) of insecticide-treated nets (ITNs) has been an important part of an overall ITN strategy to complement mass campaigns since the early 2000s. The backbone of CD implementation for many sub-Saharan African countries is distribution through antenatal care (ANC) and Expanded Programme for Immunizations (EPI) channels. Performance of these channels is often not monitored closely at the national level, nor is it reviewed globally, unlike the oversight provided to mass campaigns. The question as to why every eligible pregnant woman and child attending these services does not get an ITN remains important and yet, unanswered. Methods ANC and EPI issuing rates from seven countries were reviewed with the aim of conducting a blinded multi-country analysis. Monthly data from January to December 2021 was extracted from each country’s health management information system and analysed jointly with a National Malaria Control Programme (NMCP) focal point. VectorLink CD assessment reports were also reviewed to glean key findings. Results ITN issuing rates varied across countries at ANC (31% to 93%) and EPI (39% to 92%). Across the seven countries, the median ITN issuing rate was 64% at ANC and 78% at EPI. Results varied greatly across months per country at both ANC and EPI. NMCP focal points are aware that mass campaigns often negatively affect implementation of ITN distribution through ANC and EPI, even though global and national guidelines emphasize sustaining CD during campaigns. Concerns were also raised about the standard ITN issuing rate indicator at ANC and even more so at EPI due to the denominator. Findings from CD assessments were similar across countries: ITN stock was inconsistent and sometimes inadequate, and updated guidelines on ITN distribution and utilization and funding for social behaviour change activities were lacking at the facility level. Conclusion The importance of optimizing ANC and EPI routine channels cannot be underscored enough. They are at the frontline to protect the most biologically vulnerable populations, i.e., pregnant women and unborn and young children. Although there are encouraging signs of improvement in issuing rates with some countries reaching optimal rates, further improvements are needed to ensure that every pregnant woman and young child receives the ITN to which they are entitled

How house design affects malaria mosquito density, temperature, and relative humidity: an experimental study in rural Gambia

Introduction: Unprecedented improvements in housing are occurring across much of rural sub-Saharan Africa, but the consequences of these changes on malaria transmission remain poorly explored. We examined how different typologies of rural housing affect mosquito house entry and indoor climate. Methods: Five typologies of mud-block houses were constructed in rural Gambia: four were traditional designs with poorly fitted doors and one was a novel design with gable windows to improve ventilation. In each house, one male volunteer slept under a bednet and mosquitoes were collected indoors with a light trap. Typologies were rotated between houses weekly. Indoor conditions were monitored with data loggers and the perceived comfort of sleepers recorded with questionnaires. We used pyschrometric modelling to quantify the comfort of the indoor climate using the logger data. Primary measurements were mean number of Anopheles gambiae and mean temperature for each house typology. Findings: In thatched-roofed houses, closing the eaves reduced A gambiae house entry by 94% (95% CI 89–97) but increased the temperature compared with thatched-roofed houses with open eaves. In houses with closed eaves, those with metal roofs had more A gambiae, were hotter (1·5°C hotter [95% CI 1·3–1·7]) between 2100h and 2300 h, and had 25% higher concentrations of carbon dioxide (211·1 ppm higher [117·8–304·6]) than those with thatched roofs. In metal-roofed houses with closed eaves, mosquito house entry was reduced by 96% (91–98) by well fitted screened doors. Improved ventilation of metal-roofed houses made them as cool as thatched houses with open eaves. Metal-roofed houses with closed eaves were considered more uncomfortable than thatched ones with closed eaves. In metal-roofed houses, ventilated houses were more comfortable than unventilated houses before midnight, when people retired to bed. Interpretation: Closing the eaves reduced vector entry in thatched houses but increased entry in metal-roofed houses. Metal-roofed houses with closed eaves were, however, protected against malaria vectors by well fitted screened doors and were made comfortable by increasing ventilation. House designs that exclude mosquitoes and are comfortable to live in should be a priority in sub-Saharan Africa