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.

Concurrent amplification of Zika, chikungunya, and yellow fever virus in a sylvatic focus of arboviruses in Southeastern Senegal, 2015.

BACKGROUND: Chikungunya (CHIKV), yellow fever (YFV) and Zika (ZIKV) viruses circulate in sylvatic transmission cycles in southeastern Senegal, where they share common hosts and vectors. All three viruses undergo periodic amplifications, during which they are detected in mosquitoes and sometimes in hosts. However, little is known about their spatio-temporal patterns in years in which they undergo concurrent amplification. The aim of this study was to describe the co-amplification of ZIKV, CHIKV, and YFV, and the daily dynamics of these arboviruses and theirs vectors within villages in southeastern Senegal. RESULTS: Mosquitoes were collected monthly from July to December 2015. Each evening, from 6 to 9 PM, landing collections were performed by teams of 3 persons working simultaneously in 70 sites situated in forest (canopy and ground), savannah, agriculture, barren, and village (indoor and outdoor) land covers. Collections within villages were continued until 6 AM. Mosquitoes were tested for virus infection by virus isolation and RT-PCR. Seventy-five mosquito pools comprising 10 mosquito species contained at least one virus. Ae. furcifer and Ae. luteocephalus were infected by all three viruses, Ae. taylori by YFV and ZIKV, and remaining seven species by only, only YFV or only ZIKV. No single mosquito pool contained more than one virus. CHIKV was the only virus detected in all land cover classes and was found in the greatest number of sampling sites (32.9%, n = 70). The proportion of sites in which more than one virus was detected was less than 6%. Ae. aegypti formosus, Ae. furcifer, Ae. luteocephalus, Ae. minutus, Ae. vittatus, and An. gambiae were found within villages. These vectors were mainly active around dusk but Ae. furcifer was collected until dawn. All viruses save ZIKV were detected indoors and outdoors, mainly around dusk. Virus positive pools were detected over 2, 3 and 4 months for YFV, CHIKV and ZIKV, respectively. CONCLUSION: Our data indicate that the distribution of different vector species and different arboviruses vary substantially between sites, suggesting that CHIKV, YFV, and ZIKV may have different transmission cycles in Southeastern Senegal.

Evaluation of the residual efficacy of indoor residual spraying with bendiocarb (FICAM WP 80) in six health districts in Senegal.

BACKGROUND: From 2011 to 2014, an indoor residual spray (IRS) programme for malaria vectors control was implemented in six health districts in Senegal. The main objective of the present study was to evaluate the efficacy of bendiocarb (FICAM WP 80) sprayed on different wall surfaces and its impact on malaria vectors. The entomological monitoring activities were carried out monthly in five treated sentinel villages and one control untreated village in each district. METHODS: The residual efficacy of bendiocarb applied at a dosage of 0.4 g/sq m was monitored for a period up to 9 months post-IRS using WHO cone bioassay method. This assay consisted to expose 2-5 days old unfed susceptible Anopheles coluzzii females to sprayed walls for a period of 30 min. The mortality rates after 24 h post-exposure were estimated and compared between the different types of walls sprayed in each sentinel village. RESULTS: The results showed that the residual efficacy varied between the different sprayed walls, from one sentinel village to another and between the different campaigns. The FICAM had a residual efficacy of 3-6 months post-IRS on mud and cement wall surfaces. In some cases, the observed mortality rates were much higher than those reported elsewhere particularly during the first campaign in all the six districts. CONCLUSIONS: The FICAM was found to be effective with a residual efficacy varying from 3 to 6 months. If the quality of the IRS application is excluded as a possible explanation of the short efficacy duration, the results suggest at least two rounds of treatments in order to cover the rainy season that lasts 5 to 6 months in the area. Such treatments could be carried out before the intensification of the rains in July and August in order to better cover the transmission period that occurs between late August and October in the area.

Association of high Plasmodium falciparum parasite densities with polyclonal microscopic infections in asymptomatic children from Toubacouta, Senegal.

BACKGROUND: Malaria is a leading cause of mortality and morbidity in tropical countries, especially in sub-Saharan Africa. In Senegal, a control plan implemented in the beginning of the 2000s has enabled a substantial reduction of mortality and morbidity due to malaria. However, eradication of malaria requires a vaccine that protects against Plasmodium falciparum the deadliest species of the parasite that causes this disease. Plasmodium falciparum is characterized by an extensive genetic diversity that makes vaccine development challenging. In this study, the diversity of P. falciparum isolates was analysed from asymptomatic children residing in the district of Toubacouta, Senegal. METHODS: A nested PCR approach was used to perform genotyping of the msp-1 and msp-2 loci in samples from 87 asymptomatic children infected with P. falciparum, collected during a cross sectional survey in November and December 2010. Parasite densities in blood samples were determined by microscopic examination and statistical analyses were used to identify association of parasite genotype and parasitaemia. RESULTS: Genotyping was successful in 84/87 and 82/87 samples for msp-1 and msp-2, respectively. A strong genetic diversity was found with a total of 15 and 21 different alleles identified for msp-1 and msp-2, respectively. RO33 was the most frequent allelic family of msp-1 followed by MAD20, then by K1. Regarding msp-2 allelic families, 3D7 was more common than FC27. Multiple infections were predominant, since 69% and 89% of the samples genotyped for msp-1 and msp-2 showed more than one clone of P. falciparum with complexity of infection (COI) of 2.5 and 4.7, respectively. Expected heterozygosity (HE) was 0.57 and 0.55 for msp-1 and msp-2, respectively. Interestingly, polyclonal infections were significantly associated with higher parasitaemia. CONCLUSIONS: The strong genetic diversity of P. falciparum clones and the association of polyclonal infection with high parasitaemia call for a multi-allelic approach in the design of vaccine candidates for efficient malaria eradication.

Effects of insecticide resistance on the reproductive potential of two sub-strains of the malaria vector Anopheles coluzzii.

BACKGROUND & OBJECTIVES: The emergence and spread of insecticide resistance in African malaria vectors raise concerns over the control of malaria disease. Therefore, the implementation of better control strategies need a thorough understanding of the effects and mechanisms of resistance on vector adaptation capacities. We studied the effects of insecticide resistance on the reproductive potential of two laboratory sub-strains of the malaria vector Anopheles coluzzii characterised by phenotypic resistance/susceptibility to DDT. METHODS: The two sub-strains were selected from a laboratory strain of An. coluzzii using WHO test tubes. For each sub-strain, the number of produced and hatched eggs, developmental time, mosquito stages mortality, sex ratio and insemination rates after dissection of spermathecae were compared as measures of reproductive potential. RESULTS: Overall, the susceptible sub-strain produced higher but not significant mean numbers of eggs. However, the mean numbers of hatched eggs, larvae, pupae and adults were significantly lower than those of the resistant substrain. The mean time from egg-hatching to adult-emergence, egg-flooding to hatching, I instar to pupae and pupae to adult were similar between the two sub-strains. The mortality rates at the pupal stage were significantly different between the two sub-strains. Of the dissected spermathecae, 85.1% of the females from the resistant sub-strain were fertilized compared to 66.1% of the females from the susceptible sub-strain (p <0.0001). The resistant sub-strain produced more females in comparison to the susceptible sub-strain (respective mean sex ratio 1.37 vs 1.03, p = 0.01). INTERPRETATION & CONCLUSION: The results show differential life history traits between the two sub-strains of the malaria vector An. coluzzii, particularly fertility, insemination rate and sex ratio. They may have varied implications for insecticide resistance spread, monitoring and management; and hence underscore the need of further investigations before any generalization.

Arboviruses isolated from the Barkedji mosquito-based surveillance system, 2012-2013.

BACKGROUND: A mosquito-based arbovirus surveillance system was set up at Barkedji, Senegal after the first outbreak of Rift valley fever in West Africa in 1988. This system was recently updated using more sampling methods and collecting in greater number of ponds and villages sites. METHODS: For the current study, mosquitoes were sampled biweekly between July and December 2012 and 2013 using CDC+CO2 light traps set at ground and canopy level, mosquito nets baited with goat, sheep, human or chicken, light traps baited with goat, sheep and chicken; bird-baited traps using pigeons or chickens placed either at the ground or canopy level. Collected mosquitoes were identified, pooled and screened for arboviruses. RESULTS: A total of 42,969 mosquitoes in 4,429 pools were processed for virus isolation. Ten virus species were identified among 103 virus isolates. West Nile virus (WNV; 31 isolates), Barkedji virus (BARV; 18), Sindbis virus (SINV; 13), Usutu virus (USUV; 12), Acado virus (ACAV; 8), Ndumu virus (NDUV; 9), Sanar virus (SANV; 7), Bagaza virus (BAGV; 3), Rift valley fever virus (RVFV; 1), and Yaounde virus (YAOV; 1) were isolated from 9 ponds (91 strains) and 7 villages (12 strains). Only 3 virus species (WNV, NDU and SINV) were isolated from villages. The largest numbers of isolates were collected in October (29.1% of total isolates) and November (50.5%). Viruses were isolated from 14 mosquito species including Cx. neavei (69.9% of the strains), Cx. antennatus (9.7%), and Ma. uniformis (4.8%). NDUV, ACAV, and SINV are herein reported for the first time in the Barkedji area. Isolation of ACAV and SANV from a pool of male Ma. uniformis and USUV and BARV from a pool of male Cx. neavei, are reported for the first time to our knowledge. CONCLUSION: Our data indicate that the Barkedji area is characterized by a high diversity of viruses of medical, veterinary and unknown importance. Arboviruses were first detected in July at the beginning of the rainy season and peaked in abundance in October and November. The Barkedji area, an enzootic focus of several potentially emerging arboviruses, should be surveilled annually to be prepared to deal with future disease emergence events.

Perspectives and Challenges in Entomological Risk Assessment and Vector Control of Chikungunya.

Chikungunya virus (CHIKV) is primarily spread by the Aedes aegypti and Aedes albopictus mosquito vectors. Because there is no licensed vaccine for CHIKV, identifying ways to reduce or eliminate mosquito populations is the most effective strategy to immediately halt transmission to man. Strategies to assess the entomological risk and to control the vector are absolutely crucial to demolishing the rise of CHIKV. This review provides perspectives in entomological risk assessment and vector control, challenges for both, and gaps in knowledge that need to be addressed through rigorous research and multidisciplinary collaborations.

Potential of selected Senegalese Aedes spp. mosquitoes (Diptera: Culicidae) to transmit Zika virus.

BACKGROUND: Zika virus (ZIKV; genus Flavivirus, family Flaviviridae) is an emerging virus of medical importance maintained in a zoonotic cycle between arboreal Aedes spp. mosquitoes and nonhuman primates in African and Asian forests. Serological evidence and virus isolations have demonstrated widespread distribution of the virus in Senegal. Several mosquito species have been found naturally infected by ZIKV but little is known about their vector competence. METHODS: We assessed the vector competence of Ae. aegypti from Kedougou and Dakar, Ae. unilineatus, Ae. vittatus and Ae. luteocephalus from Kedougou in Senegal for 6 ZIKV strains using experimental oral infection. Fully engorged female mosquitoes were maintained in an environmental chamber set at 27 ± 1 °C and 80 ± 5% Relative humidity. At day 5, 10 and 15 days post infection (dpi), individual mosquito saliva, legs/wings and bodies were tested for the presence of ZIKV genome using real time RT-PCR to estimate the infection, dissemination, and transmission rates. RESULTS: All the species tested were infected by all viral strains but only Ae. vittatus and Ae. luteocephalus were potentially capable of transmitting ZIKV after 15 dpi with 20 and 50% of mosquitoes, respectively, delivering epidemic (HD 78788) and prototype (MR 766) ZIKV strains in saliva. CONCLUSION: All the species tested here were susceptible to oral infection of ZIKV but only a low proportion of Ae. vittatus and Ae. luteocephalus had the viral genome in their saliva and thus the potential to transmit the virus. Further investigations are needed on the vector competence of other species associated with ZIKV for better understanding of the ecology and epidemiology of this virus in Senegal.

Anopheles arabiensis seasonal densities and infection rates in relation to landscape classes and climatic parameters in a Sahelian area of Senegal.

BACKGROUND: The influence of environmental and climatic factors on malaria vector bionomics and transmission is an important topic in the context of climatic change particularly at macro-geographical level. Sahelian areas could be particularly affected due to heterogeneous features including high inter-annual variability in rainfall and others associated parameters. Therefore, baseline information on the impact of environmental and climatic factors on malaria transmission at micro-geographical level is required for vector risk management and implementation of control strategies. METHODS: Malaria vectors were collected indoors by pyrethrum spray catches in 14 villages belonging to 4 different landscape classes (wooded savanna, shrubby savanna, bare soils and steppe) in the sylvo-pastoral area of Senegal. Plasmodium falciparum infection rates were determined using an indirect enzyme-linked immunosorbent assay (ELISA). RESULTS: An. arabiensis was the predominant species in all landscape classes and was the only species collected at the end of the rainy season excepted in villages located in bare soils where it cohabited with An. coluzzii. Mean temperature and relative humidity showed similar variations in all the landscape classes covered whereas rainfall was more heterogeneous in terms of pattern, frequency and amount. The mean densities of An. arabiensis displayed high seasonal differences with peaks observed in August or September. A positive non-significant correlation was observed between An. arabiensis densities for rainfall and humidity whereas a negative non-significant correlation was reported for temperature. Plasmodium falciparum-infected mosquitoes were detected only in wooded savanna and bare soils villages. CONCLUSIONS: These observations suggest key roles played by landscape classes and rainfall in malaria vector densities, infection rates and malaria transmission that could be more pronounced in villages situated in wooded savanna and bare soils. Due to the close relationship between environmental and meteorological parameters in this Sahelian region, additional studies on the impact of these parameters are required to further ascertain their association with entomological parameters involved in malaria transmission. From the public health point of view, such information could be useful for human population settlements as well as for monitoring and modelling purposes giving early warning system for implementation of interventions in these unstable transmission zones.

Dengue 1 outbreak in Rosso, northern Senegal, October 2021: entomologic investigations.

Senegal has experienced periodic epidemics of dengue in urban areas with increased incidence in recent years. However, few data are available on the local ecology of the epidemic vectors. In October 2021, a dengue outbreak was reported in northern Senegal to the Institute Pasteur de Dakar. Entomologic investigations then were undertaken to identify the areas at risk of transmission and to identify the vector(s). Adult mosquitoes were collected indoors and outdoors at selected households, while containers with water were inspected for mosquito larvae. All the Aedes aegypti (L.) collected were tested for dengue virus NS1 protein using a rapid diagnostic test (RDT), and positive samples were confirmed by real-time RT-PCR. The qRT-PCR positive samples were subjected to whole genome sequencing using Nanopore technology. The majority of the larvae-positive containers (83.1%) were used for water storage. The Breteau and Container indices exceeded the WHO-recommended thresholds for the risk of dengue virus transmission except at 2 localities. Ae. aegypti, the only reputed dengue vector, was collected resting indoors as well as outdoors and biting during the day and night. The NS1 protein was detected in 22 mosquito pools, including one pool of females emerging from field-collected larvae. All NS1-positive results were confirmed by RT-PCR. Virus serotyping showed that the outbreak was caused by DENV-1. This study demonstrates the need for continuous control of adult and aquatic stages of Ae. aegypti to prevent future dengue epidemics in Senegal. RDTs appear to be a promising tool for dengue diagnostics and surveillance.

Insecticide Resistance and Target-Site Mutations kdr, N1575Y, and Ace-1 in Anopheles gambiae s.l. Populations in a Low-Malaria-Transmission Zone in the Sudanian Region of Senegal.

Background/Objectives: Significant progress in malaria control has been achieved through long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS), raising hopes for malaria elimination. However, emerging insecticide resistance threatens these gains. This study assessed the susceptibility of Anopheles gambiae s.l. populations to public health insecticides, examined the frequencies of kdr, Ace-1, and N1575Y mutations, and explored their associations with phenotypic resistance in Dielmo and Ndiop, Senegal. Methods: Anopheles larvae collected between September and December 2022 were reared to adulthood. Adult mosquitoes were exposed to discriminating concentrations of various insecticides following WHO guidelines. Knockdown times (KDT50 and KDT95) for pyrethroids were calculated using the Probit model. RT-qPCR detected target-site mutations (kdr: L1014F and L1014S, Ace-1, N1575Y) and assessed correlations with phenotypic resistance. Species-specific PCR identified species within the An. gambiae complex. Results/Conclusions: The populations of Dielmo and Ndiop showed susceptibility to pirimiphos-methyl and bendiocarb, with no Ace-1 mutation detected. Resistance to DDT and pyrethroids was observed. The knockdown times indicated that alphacypermethrin and lambdacyhalothrin were more effective than permethrin and deltamethrin. The L1014F allele was widespread, while L1014S was absent in Ndiop and low in Dielmo. The N1575Y mutation occurred only in populations with L1014F. The L1014S mutation was significantly associated with resistance to lambdacyhalothrin in both villages and to deltamethrin in Ndiop.

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).

Persistent carriage of subpatent Plasmodium falciparum parasites associated with clinical malaria in a low transmission area in Senegal.

OBJECTIVES: In low malaria transmission areas, the elimination of the disease has been hampered partly by the existence of a reservoir of subpatent Plasmodium falciparum infections within communities. This reservoir, often undetected, serves as a source of parasites and contributes to ongoing transmission and clinical malaria cases. METHODS: This study, spanning a period of 9 years from June 2014 to December 2022, examined individual variations and long-term subpatent P. falciparum carriage in two matched cohorts of 44 individuals each living in Dielmo village in the Sudanian area of Senegal. Biannual blood samples, collected in June/July and December of each year, underwent P. falciparum diagnosis by quantitative polymerase chain reaction. QGIS and R analytical tools were used to map infections, assess the occurrence and clustering of subpatent and clinical P. falciparum infections, and determine the risk of infection in the vicinity of asymptomatic P. falciparum carriers. RESULTS: The point frequency and long-term P. falciparum carriage were significantly higher among the quantitative polymerase chain reaction (qPCR) positive cohort compared to the negative cohort across the 16 cross-sectional surveys analyzed in this study (19.76% vs 10.99%, P-value <0.001). Asymptomatic carriage events in qPCR-positive group were 18.86 ± 1.72% and significantly greater (P-value = 0.001) than in the qPCR-negative group (11.32 ± 1.32%). The relative risk of P. falciparum infection or clinical malaria calculated with a 95% confidence interval significantly increased in the vicinity of infected individuals and was 1.44 (P-value = 0.53) and 2.64 (P-value = 0.04) when at least one individual in the direct (household) or indirect (block of households) vicinity is infected, respectively. The risk increased to 3.64 (P-value <0.001) if at least 1/5 of individuals in the indirect vicinity were P. falciparum-infected. CONCLUSIONS: The study provides a detailed qualitative and quantitative analysis of the asymptomatic P. falciparum reservoir and its temporal and spatial dynamics within two subgroups of P. falciparum-infected and non-infected individuals in Dielmo village. It identified high-risk populations known as "hotpops" and hotspots that could be targeted by innovative interventions to accelerate the elimination of malaria in Dielmo village.

Differential insecticide resistance in Anopheles arabiensis populations in the seaside area of Mbour and its suburbs in Senegal.

Regular monitoring of insecticide resistance status is an important step in implementing appropriate and adapted insecticide-based strategies for vector control. In Senegal, Indoor Residual Spraying (IRS) and a national distribution campaign for long-lasting insecticide-treated net (LLIN) have been implemented since 2007 and 2009, respectively to prevent malaria transmission. To expand and ensure the sustainability of these strategies, we conducted a study on the status of insecticide resistance in malaria vectors in the seaside area of Mbour and its suburbs where no data were previously available. Anopheles larvae were sampled from four study sites (two in both coastal and inland areas) and reared to adulthood in the insectarium. Non-blood-fed females aged 3-5 days were then tested for susceptibility to permethrin, deltamethrin, lambdacyhalothrin, bendiocarb and pirimiphos-methyl. PCR amplification was used to identify sibling species of the An. gambiae complex and genotyping for the presence of resistance knockdown (kdr) L1014S, L1014F and Ace-1 G119S. Anopheles arabiensis was the only species present in the area. At all four sites, mosquitoes were resistant to deltamethrin, permethrin, and lambdacyhalothrin, and exhibited varying degrees of resistance to bendiocarb and pirimiphos-methyl. Overall, high levels of leucine-serine/phenylalanine substitutions at position 1014 (L1014S/L1014F) were observed, with frequencies ranging from 76.4 to 85.2 % for L1014F, and from 43.2 to 66.7 % for L1014S, compared to 8.1 to 28.3 for the Ace-1 G119S mutation. These results indicate a high level of phenotypic and genotypic resistance to insecticides, which is alarming, as it could have a significant impact on the operational effectiveness of current vector control tools that rely on pyrethroids. However, in the case of bendiocarb and pirimiphos-methyl, while some level of tolerance was observed, their potential use requires regular monitoring to prevent operational failure, as their deployment could potentially lead to an increase in resistance to them.

A High Proportion of Malaria Vector Biting and Resting Indoors despite Extensive LLIN Coverage in Côte d'Ivoire.

Malaria is still a leading cause mortality in Côte d'Ivoire despite extensive LLINs coverage. We present the results of an entomological survey conducted in a coastal and in an inland village with the aim to estimate Anopheles gambiae sensu lato (s.l.) female's abundance indoor/outdoor and Plasmodium falciparum infection rate and analyze the occurrence of blood-feeding in relation to LLINs use. Pyrethrum spray (PSC) and window exit traps (WT) collections were carried out to target endophagic/endophilic and endophagic/exophilic females, respectively. Data on LLINs use in sampled houses were collected. (1) high levels of malaria transmission despite LLINs coverage >70% (~1 An. gambiae s.l. predicted mean/person/night and ~5% Plasmodium falciparum infection rate); (2) 46% of females in the PSC sample were blood-fed, suggesting that they fed on an unprotected host inside the house; (3) 81% of females in WT were unfed, suggesting that they were leaving the house to find an available host. Model estimates that if everyone sleeps under LLINs the probability for a mosquito to bite decreases of 48% and 95% in the coastal and inland village, respectively. The results show a high proportion of mosquito biting and resting indoors despite extensive LLINs. The biological/epidemiological determinants of accounting for these results merit deeper investigations.

Characterization of the swarming behavior of Anopheles coluzzii and Anopheles gambiae (Diptera: Culicidae) populations in a hybrid zone of Senegal.

Anopheles gambiae and Anopheles coluzzii, often found in sympatry and synchronous, have undergone a premating reproductive isolation across their distribution range. However, in the Western coast of Africa, unexpected hybridization zones have been observed, and little is known about swarming behavior of these cryptic taxa. Here, we characterized the swarming behavior of An. coluzzii and An. gambiae to investigate its role in the high hybridization level in Senegal. The study was conducted in the south and central Senegal during the 2018 rainy season. Mating swarms of malaria vectors were surveyed at sunset and collected using an insect net. Meanwhile, indoor resting populations of malaria vectors were collected by pyrethrum spray catches. Upon collection, specimens were identified morphologically, and then members of the An. gambiae complex were identified at the species level by polymerase chain reaction (PCR). An. gambiae swarmed mainly over bare ground, whereas An. coluzzii were found swarming above various objects creating a dark-light contrast with the bare ground. The swarms height varied from 0.5 to 2.5 m. Swarming starting time was correlated with sunset whatever the months for both species, and generally lasted about 10 min. No mixed swarm of An. gambiae and An. coluzzii was found even in the high hybridization area. These results indicated a premating isolation between An. coluzzii and An. gambiae. However, the high hybridization rate in the sympatric area suggests that heterogamous mating is occurring, thus stressing the need for further extensive studies.

Assessment of the Risk of Exotic Zika Virus Strain Transmission by Aedes aegypti and Culex quinquefasciatus from Senegal Compared to a Native Strain.

Zika virus (ZIKV) shows an enigmatic epidemiological profile in Africa. Despite its frequent detection in mosquitoes, few human cases have been reported. This could be due to the low infectious potential or low virulence of African ZIKV lineages. This study sought to assess the susceptibility of A. aegypti and C. quinquefasciatus to ZIKV strains from Senegal, Brazil, and New Caledonia. Vertical transmission was also investigated. Whole bodies, legs/wings and saliva samples were tested for ZIKV by real-time PCR to estimate infection, dissemination and transmission rates as well as the infection rate in the progeny of infected female A. aegypti. For A. aegypti, the Senegalese strain showed at 15 days post-exposure (dpe) a significantly higher infection rate (52.43%) than the Brazilian (10%) and New Caledonian (0%) strains. The Brazilian and Senegalese strains were disseminated but not detected in saliva. No A. aegypti offspring from females infected with Senegalese and Brazilian ZIKV strains tested positive. No infection was recorded for C. quinquefasciatus. We observed the incompetence of Senegalese A. aegypti to transmit ZIKV and the C. quinquefasciatus were completely refractory. The effect of freezing ZIKV had no significant impact on the vector competence of Aedes aegypti from Senegal, and vertical transmission was not reported in this study.

Host feeding preferences of malaria vectors in an area of low malaria transmission.

Studying the behaviour and trophic preferences of mosquitoes is an important step in understanding the exposure of vertebrate hosts to vector-borne diseases. In the case of human malaria, transmission increases when mosquitoes feed more on humans than on other animals. Therefore, understanding the spatio-temporal dynamics of vectors and their feeding preferences is essential for improving vector control measures. In this study, we investigated the feeding behaviour of Anopheles mosquitoes at two sites in the Sudanian areas of Senegal where transmission is low following the implementation of vector control measures. Blood-fed mosquitoes were collected monthly from July to November 2022 by pyrethrum spray catches in sleeping rooms of almost all houses in Dielmo and Ndiop villages, and blood meals were identified as from human, bovine, ovine, equine and chicken by ELISA. Species from the An. gambiae complex were identified by PCR. The types and numbers of potential domestic animal hosts were recorded in each village. The Human Blood Index (HBI) and the Manly Selection Ratio (MSR) were calculated to determine whether hosts were selected in proportion to their abundance. Spatio-temporal variation in HBI was examined using the Moran's index. A total of 1251 endophilic Anopheles females were collected in 115 bedrooms, including 864 blood fed females of 6 species. An. arabiensis and An. funestus were predominant in Dielmo and Ndiop, respectively. Of the 864 blood meals tested, 853 gave a single host positive result mainly on bovine, equine, human, ovine and chicken in decreasing order in both villages. Overall, these hosts were not selected in proportion to their abundance. The human host was under-selected, highlighting a marked zoophily for the vectors. Over time and space, the HBI were low with no obvious trend, with higher and lower values observed in each of the five months at different points in each village. These results highlight the zoophilic and exophagic behaviour of malaria vectors. This behaviour is likely to be a consequence of the distribution and use of LLINs in both villages and may increase risk of residual outdoor transmission. This underlines the need to study the feeding host profile of outdoor resting populations and how domestic animals may influence malaria epidemiology in order to tailor effective malaria vector control strategies in the two villages.

Detection of Crimean-Congo Haemorrhagic Fever Virus from Livestock Ticks in Northern, Central and Southern Senegal in 2021.

Crimean-Congo haemorrhagic fever virus (CCHFV) occurs sporadically in Senegal, with a few human cases each year. This active circulation of CCHFV motivated this study which investigated different localities of Senegal to determine the diversity of tick species, tick infestation rates in livestock and livestock infections with CCHFV. The samples were collected in July 2021 from cattle, sheep and goats in different locations in Senegal. Tick samples were identified and pooled by species and sex for CCHFV detection via RT-PCR. A total of 6135 ticks belonging to 11 species and 4 genera were collected. The genus Hyalomma was the most abundant (54%), followed by Amblyomma (36.54%), Rhipicephalus (8.67%) and Boophilus (0.75%). The prevalence of tick infestation was 92%, 55% and 13% in cattle, sheep and goats, respectively. Crimean-Congo haemorrhagic fever virus (CCHFV) was detected in 54/1956 of the tested pools. The infection rate was higher in ticks collected from sheep (0.42/1000 infected ticks) than those from cattle (0.13/1000), while all ticks collected from goats were negative. This study confirmed the active circulation of CCHFV in ticks in Senegal and highlights their role in the maintenance of CCHFV. It is imperative to take effective measures to control tick infestation in livestock to prevent future CCHFV infections in humans.

Impact of mosquito bites on asexual parasite density and gametocyte prevalence in asymptomatic chronic Plasmodium falciparum infections and correlation with IgE and IgG titers.

An immunomodulatory role of arthropod saliva has been well documented, but evidence for an effect on Plasmodium sp. infectiousness remains controversial. Mosquito saliva may orient the immune response toward a Th2 profile, thereby priming a Th2 response against subsequent antigens, including Plasmodium. Orientation toward a Th1 versus a Th2 profile promotes IgG and IgE proliferation, respectively, where the former is crucial for the development of an efficient antiparasite immune response. Here we assessed the direct effect of mosquito bites on the density of Plasmodium falciparum asexual parasites and the prevalence of gametocytes in chronic, asymptomatic infections in a longitudinal cohort study of seasonal transmission. We additionally correlated these parasitological measures with IgE and IgG antiparasite and anti-salivary gland extract titers. The mosquito biting density was positively correlated with the asexual parasite density but not asexual parasite prevalence and was negatively correlated with gametocyte prevalence. Individual anti-salivary gland IgE titers were also negatively correlated with gametocyte carriage and were strongly positively correlated with antiparasite IgE titers, consistent with the hypothesis that mosquito bites predispose individuals to develop an IgE antiparasite response. We provide evidence that mosquito bites have an impact on asymptomatic infections and differentially so for the production of asexual and sexual parasites. An increased research focus on the immunological impact of mosquito bites during asymptomatic infections is warranted, to establish whether strategies targeting the immune response to saliva can reduce the duration of infection and the onward transmission of the parasite.