Distribution and dynamics of Anopheles gambiae s.l. larval habitats in three Senegalese cities with high urban malaria incidence.

Urban malaria has become a challenge for most African countries due to urbanization, with increasing population sizes, overcrowding, and movement into cities from rural localities. The rapid expansion of cities with inappropriate water drainage systems, abundance of water storage habitats, coupled with recurrent flooding represents a concern for water-associated vector borne diseases, including malaria. This situation could threaten progress made towards malaria elimination in sub-Saharan countries, including Senegal, where urban malaria has presented as a threat to national elimination gains. To assess drivers of urban malaria in Senegal, a 5-month study was carried out from August to December 2019 in three major urban areas and hotspots for malaria incidence (Diourbel, Touba, and Kaolack) including the rainy season (August-October) and partly dry season (November-December). The aim was to characterize malaria vector larval habitats, vector dynamics across both seasons, and to identify the primary eco- environmental entomological factors contributing to observed urban malaria transmission. A total of 145 Anopheles larval habitats were found, mapped, and monitored monthly. This included 32 in Diourbel, 83 in Touba, and 30 in Kaolack. The number of larval habitats fluctuated seasonally, with a decrease during the dry season. In Diourbel, 22 of the 32 monitored larval habitats (68.75%) were dried out by December and considered temporary, while the remaining 10 (31.25%) were classified as permanent. In the city of Touba 28 (33.73%) were temporary habitats, and of those 57%, 71% and 100% dried up respectively by October, November, and December. However, 55 (66.27%) habitats were permanent water storage basins which persisted throughout the study. In Kaolack, 12 (40%) permanent and 18 (60%) temporary Anopheles larval habitats were found and monitored during the study. Three malaria vectors (An. arabiensis, An. pharoensis and An. funestus s.l.) were found across the surveyed larval habitats, and An. arabiensis was found in all three cities and was the only species found in the city of Diourbel, while An. arabiensis, An. pharoensis, and An. funestus s.l. were detected in the cities of Touba and Kaolack. The spatiotemporal observations of immature malaria vectors in Senegal provide evidence of permanent productive malaria vector larval habitats year-round in three major urban centers in Senegal, which may be driving high urban malaria incidence. This study aimed to assess the presence and type of anopheline larvae habitats in urban areas. The preliminary data will better inform subsequent detailed additional studies and seasonally appropriate, cost-effective, and sustainable larval source management (LSM) strategies by the National Malaria Control Programme (NMCP).

Urban malaria vector bionomics and human sleeping behavior in three cities in Senegal.

BACKGROUND: Malaria is endemic in Senegal, with seasonal transmission, and the entire population is at risk. In recent years, high malaria incidence has been reported in urban and peri-urban areas of Senegal. An urban landscape analysis was conducted in three cities to identify the malaria transmission indicators and human behavior that may be driving the increasing malaria incidence occurring in urban environments. Specifically, mosquito vector bionomics and human sleeping behaviors including outdoor sleeping habits were assessed to guide the optimal deployment of targeted vector control interventions. METHODS: Longitudinal entomological monitoring using human landing catches and pyrethrum spray catches was conducted from May to December 2019 in Diourbel, Kaolack, and Touba, the most populous cities in Senegal after the capital Dakar. Additionally, a household survey was conducted in randomly selected houses and residential Koranic schools in the same cities to assess house structures, sleeping spaces, sleeping behavior, and population knowledge about malaria and vector control measures. RESULTS: Of the 8240 Anopheles mosquitoes collected from all the surveyed sites, 99.4% (8,191) were An. gambiae s.l., and predominantly An. arabiensis (99%). A higher number of An. gambiae s.l. were collected in Kaolack (77.7%, n = 6496) than in Diourbel and Touba. The overall mean human biting rate was 14.2 bites per person per night (b/p/n) and was higher outdoors (15.9 b/p/n) than indoors (12.5 b/p/n). The overall mean entomological inoculation rates ranged from 3.7 infectious bites per person per year (ib/p/y) in Diourbel to 40.2 ib/p/y in Kaolack. Low anthropophilic rates were recorded at all sites (average 35.7%). Of the 1202 households surveyed, about 24.3% of household members slept outdoors, except during the short rainy season between July and October, despite understanding how malaria is transmitted and the vector control measures used to prevent it. CONCLUSION: Anopheles arabiensis was the primary malaria vector in the three surveyed cities. The species showed an outdoor biting tendency, which represents a risk for the large proportion of the population sleeping outdoors. As all current vector control measures implemented in the country target endophilic vectors, these data highlight potential gaps in population protection and call for complementary tools and approaches targeting outdoor biting malaria vectors.

Evaluation of the residual efficacy and physical durability of five long-lasting insecticidal nets (LLINs) in Senegal.

BACKGROUND: The preventive and curative strategies of malaria are based on promoting the use of long-lasting insecticidal nets (LLINs) and treating confirmed cases with artemisinin-based combination therapy. These strategies have led to a sharp decline in the burden of malaria, which remains a significant public health problem in sub-Saharan countries. The objective of this study was to determine and compare the residual efficacy of LLINs recommended by the World Health Organization. METHODS: The study was conducted in six villages in two sites in Senegal located in the Sahelo-Sudanian area of the Thiès region, 70 km from Dakar and in Mbagame, a semi-urban zone in the Senegal River Valley. A census was conducted of all sleeping places in each household to be covered by LLINs. Five brands of LLIN were distributed, and every six months, retention rates, net use, maintenance, physical integrity, insecticide chemical content, and biological efficacy were examined for each type of LLIN. RESULTS: A total of 3012 LLINs were distributed in 1249 households in both sites, with an average coverage rate of 94% (95% CI 92.68-95.3). After 36 months, the average retention rate was 12.5% and this rate was respectively 20.5%, 15.1%, 10%, 7%, and 3% for Olyset Net®, Dawa Plus® 2.0, PermaNet® 2.0, NetProtect® and Life Net®, respectively. The proportion of LLINs with holes and the average number of holes per mosquito net increased significantly during each follow-up, with a large predominance of size 1 (small) holes for all types of LLINs distributed. During the three-year follow-up, bioassay mortality rates of a susceptible strain of insectary reared Anopheles coluzzii decreased in the following net types: in Dawa Plus® 2.0 (100% to 51.7%), PermaNet® 2.0 (96.6% to 83%), and Olyset Net® (96.6% to 33.3%). Mortality rates remained at 100% in Life Net® over the same time period. After 36 months, the average insecticide content per brand of LLIN decreased by 40.9% for Dawa Plus® 2.0, 31% for PermaNet® 2.0, 39.6% for NetProtect® and 51.9% for Olyset Net® and 40.1% for Life Net. CONCLUSIONS: Although some net types retained sufficient insecticidal activity, based on all durability parameters measured, none of the net types survived longer than 2 years.

Survival of eight LLIN brands 6, 12, 24 and 36 months after a mass distribution campaign in rural and urban settings in Senegal.

BACKGROUND: Long lasting insecticidal nets (LLIN) are one of the core components of global malaria prevention and control. The lifespan of LLIN varies widely depending on the population or environment, and randomized studies are required to compare LLIN inaccording to arbitrary thresholds households under different field conditions. This study investigated survival of different LLIN brands in Senegal. METHODS: Ten thousand six hundred eight LLINs were distributed in five regions, each stratified by rural and urban setting. As part of the longitudinal follow-up, 2222 nets were randomly sampled and monitored from 6 to 36 months. Using random effects for households, Bayesian models were used to estimate independent survival by net type (Interceptor®, Life Net®, MAGNet™, Netprotect®, Olyset® Net, PermaNet® 2.0 R, PermaNet® 2.0 C, Yorkool® LN) and by area (rural/urban). In addition to survival, median survival time and attrition of each LLIN brand was determined. Attrition was defined as nets that were missing because they were reported given away, destroyed and thrown away, or repurposed. RESULTS: Three net types had a proportion of survival above 80% after 24 months: Interceptor®87.8% (95% CI 80-93.4); conical PermaNet® 2.0 86.9% (95% CI 79.3-92.4) and Life Net® 85.6% (95% CI 75-93). At 36 months, conical PermaNet® 2.0 maintained a good survival rate, 79.5% (95% CI 65.9-88.8). The attrition due to redistributed nets showed that the two conical net types (PermaNet® 2.0 and Interceptor®) were more often retained by households and their median retention time was well above 3 years (median survival time = 3.5 years for PermaNet® 2.0 and median survival time = 4 years for Interceptor®). Despite this good retention, Interceptor® had weak physical integrity and its median survival due to wear and tear was below 3 years (median survival time = 2.4 years). The odds ratio of survival was 2.5 times higher in rural settings than in urban settings (OR 2.5; 95% CI 1.7-3.7). CONCLUSIONS: Differences in survival among LLIN may be driven by brand, shape or environmental setting. In this study in Senegal, conical PermaNet® 2.0 were retained in households while rectangular PermaNet® 2.0 had lower retention, suggesting that net shape may play a role in retention and should be further investigated. Distribution of preferred LLIN shape, accompanied by good communication on care and repair, could lead to increased effective lifespan, and allow for longer intervals between universal coverage campaigns.

Multiple insecticide resistance target sites in adult field strains of An. gambiae (s.l.) from southeastern Senegal.

BACKGROUND: High coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the cornerstones of vector control strategy in Senegal where insecticide resistance by the target vectors species is a great of concern. This study explores insecticide susceptibility profile and target-site mutations mechanisms within the Anopheles gambiae complex in southeastern Senegal. METHODS: Larvae of Anopheles spp. were collected in two sites from southeastern Senegal Kedougou and Wassadou/Badi in October and November 2014, and reared until adult emergence. Wild F0 adult mosquitoes were morphologically identified to species. Susceptibility of 3-5-day-old An. gambiae (s.l.) samples to 11 insecticides belonging to the four insecticide classes was assessed using the WHO insecticide susceptibility bioassays. Tested samples were identified using molecular techniques and insecticide resistance target-site mutations (kdr, ace-1 and rdl) were determined. RESULTS: A total of 3742 An. gambiae (s.l.) were exposed to insecticides (2439 from Kedougou and 1303 from Wassadou-Badi). Tests with pyrethroid insecticides and DDT showed high level of resistance in both Kedougou and Wassadou/Badi. Resistance to pirimiphos-methyl and malathion was not detected while resistance to bendoicarb and fenitrothion was confirmed in Kedougou. Of the 745 specimens of An. gambiae (s.l.) genotyped, An. gambiae (s.s.) (71.6%) was the predominant species, followed by An. arabiensis (21.7%), An. coluzzii (6.3%) and hybrids (An. gambiae (s.s.)/An. coluzzii; 0.4%). All target site mutations investigated (Vgsc-1014F, Vgsc-1014S, Ace-1 and Rdl) were found at different frequencies in the species of the Anopheles gambiae complex. Vgsc-1014F mutation was more frequent in An. gambiae (s.s.) and An. coluzzii than An. arabiensis. Vgsc-1014S was present in An. gambiae (s.l.) populations in Wassadou but not in Kedougou. Ace-1 and rdl mutations were more frequent in An. gambiae (s.s.) in comparison to An. arabiensis and An. coluzzii. CONCLUSIONS: Resistance to all the four insecticide classes tested was detected in southeastern Senegal as well as all target site mutations investigated were found. Data will be used by the national Malaria Control Programme.