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

OBJECTIVE: 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 contribute to ongoing transmission and clinical malaria cases. METHODS: This study, spanning a period of nine 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 qPCR positive cohort compared to the negative cohort across the 16 cross-sectional surveys analysed 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. CONCLUSION: 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 hotpops and hotspots that could be targeted by innovative interventions to accelerate the elimination of malaria in Dielmo village.

Malaria epidemics associated with low net use in preadolescent and young adult population in Dielmo (Senegal), a malaria pre-elimination area.

BACKGROUND: The epidemic rebounds observed in 2010 and 2013 in Dielmo, a Senegalese village, during a decade (2008-2019) of universal coverage using a long-lasting insecticidal net (LLIN) strategy could have contributed to the resurgence of malaria. Thus, this study was undertaken to understand the implications of net ownership and use on malaria rebound events. METHODS: A longitudinal study was carried out in Dielmo with 11 years of LLIN implementation from July 2008 to June 2019 with successive net renewals in 2011, 2014, 2016 and 2019. Quarterly cross-sectional surveys were performed to assess LLIN ownership and use by different age groups in the population. In addition, malaria incidence and transmission were assessed during the study period. RESULTS: Ownership of LLINs decreased significantly from 88% in the 1st year of net implementation to 70% during the first malaria upsurge and 72% during the second upsurge while net use decreased significantly from 66% during the 1st year to 58% during the first malaria upsurge and 53% during the second upsurge. Among young adults aged 15-29 years, net use decreased significantly from the 2nd year (51%) of net use to reach 43% during the first malaria upsurge and only 32% use during the second malaria upsurge. During the second malaria upsurge, net use was significantly lower among older children aged 10-14 years old than during the 1st year of net use (p < 0.001). During the first and the second malaria upsurges, the malaria incidence was significantly higher among children aged 10-14 years old (0.4 attacks per person-year) and young adults aged 15-29 years old (0.3 and 0.4 attacks per person, respectively) than during that the 1st year of net implementation (only 0.02 attacks per person-year for 10-14 year olds and 0.04 for 15-29 year olds; p < 0.001). CONCLUSIONS: The first malaria upsurge occurred following a progressive decrease in net use after the 2nd year of their implementation with an important increase in malaria incidence among older children while the second malaria upsurge was significantly associated with the decrease of net use among older children and young adults. The regular use of nets in all age groups prevented the occurrence of a third malaria upsurge in Dielmo.

One hundred malaria attacks since birth. A longitudinal study of African children and young adults exposed to high malaria transmission.

Background: Despite significant progress in malaria control over the past twenty years, malaria remains a leading cause of child morbidity and mortality in Tropical Africa. As most patients do not consult any health facility much uncertainty persists about the true burden of the disease and the range of individual differences in susceptibility to malaria. Methods: Over a 25-years period, from 1990 to 2015, the inhabitants of Dielmo village, Senegal, an area of intense malaria transmission, have been monitored daily for their presence in the village and the occurrence of diseases. In case of fever thick blood films were systematically examined through microscopy for malaria parasites and patients received prompt diagnosis and treatment. Findings: We analysed data collected in 111 children and young adults monitored for at least 10 years (mean 17.3 years, maximum 25 years) enrolled either at birth (95 persons) or during the two first years of life. A total of 11,599 episodes of fever were documented, including 5268 malaria attacks. The maximum number of malaria attacks in a single person was 112. Three other persons suffered one hundred or more malaria attacks during follow-up. The minimum number of malaria attacks in a single person was 11. The mean numbers of malaria attacks in children reaching their 4th, 7th, and 10th birthdays were 23.0, 37.7, and 43.6 attacks since birth, respectively. Sixteen children (14.4%) suffered ten or more malaria attacks each year at ages 1-3 years, and six children (5.4%) each year at age 4-6 years. Interpretation: Long-term close monitoring shows that in highly endemic areas the malaria burden is higher than expected. Susceptibility to the disease may vary up to 10-fold, and for most children childhood is an endless history of malaria fever episodes. No other parasitic, bacterial or viral infection in human populations has such an impact on health. Funding: The Pasteur Institutes of Dakar and Paris, the Institut de Recherche pour le Développement, and the French Ministry of Cooperation provided funding.

Plasmodium falciparum population structure and genetic diversity of cell traversal protein for ookinetes and sporozoites (CelTOS) during malaria resurgences in Dielmo, Senegal.

The ability to accurately measure the intensity of malaria transmission in areas with low transmission is extremely important to guide elimination efforts. Plasmodium falciparum Cell-traversal protein for ookinetes and sporozoites (PfCelTOS) is an important conserved sporozoite antigen reported as one of the promising malaria vaccine candidates, and could be used to estimate malaria transmission intensity. This study aimed at determining whether the diversity of PfCelTOS gene reflects the changes in malaria transmission that occurred between 2007 and 2014 in Dielmo, a Senegalese village, before and after the implementation of insecticide treated bed nets (ITNs). Of the 109 samples positive for PfCelTOS PCR, 96 (88%) were successfully sequenced and analysed for polymorphisms and population diversity. The number of segregating sites was higher during the pre-intervention period (13) and the malaria resurgences (11) than during the intervention period (5). Similarly, the number and diversity of haplotypes were higher during the pre-intervention period (16 and 0.914, respectively) and the malaria resurgences (6 and 0.821, respectively) than during the intervention period (4 and 0.758, respectively). Moreover, the average number of nucleotide differences was higher during the pre-intervention (3.792) and during malaria resurgences (3.467) than during the intervention period (2.189). The 3D7 KSSFNEP haplotype was only observed during the intervention period. Only two haplotypes were shared in both the pre-intervention and intervention periods while four haplotypes were shared between the pre-intervention and the malaria resurgences. The Fst values indicate moderate differentiation between pre-intervention and intervention periods (0.17433), and between intervention and malaria resurgences period (0.19198) as well as between pre-intervention and malaria resurgences periods (0.06607). PfCelTOS genetic diversity reflected changes of malaria transmission, with higher polymorphisms recorded before the large-scale implementation of ITNs and during the malaria resurgences. PfCelTOS is also a candidate vaccine; mapping its diversity across multiple endemic environments will facilitate the design and optimisation of a broad and efficacious vaccine.

Rebound of multiple infections and prevalence of anti-malarial resistance associated markers following malaria upsurges in Dielmo village, Senegal, West Africa.

BACKGROUND: Thanks to the scale up of malaria control interventions, the malaria burden in Senegal has decreased substantially to the point that the National Malaria Control Programme plans to achieve malaria elimination by 2030. To guide such efforts, measuring and monitoring parasite population evolution and anti-malarial drugs resistance is extremely important. Information on the prevalence of parasite mutations related to drug resistance can provide a first signal of emergence, introduction and selection that can help with refining drug interventions. The aim of this study was to analyse the prevalence of anti-malarial drug resistance-associated markers before and after the implementation of artemisinin-based combination therapy (ACT) from 2005 to 2014 in Dielmo, a model site for malaria intervention studies in Senegal. METHODS: Samples from both malaria patients and Plasmodium falciparum asymptomatic carriers were analysed with high resolution melting (HRM) technique to genotype P. falciparum chloroquine resistance transporter (Pfcrt) gene haplotypes and multidrug-resistant protein 1 (Pfmdr1) gene at codons N86 and Y184. RESULTS: Among the 539 samples analysed, 474, 486, and 511 were successfully genotyped for Pfmdr1 N86, Y184, and Pfcrt, respectively. The prevalence of drug resistance markers was high, particularly during the malaria upsurges. Following the scale-up in bed net distribution, only the mutant (86F-like) variant of Pfmdr1 86 was present while during the malaria upsurges the predominance of two types 86Y-86N (43%) and 86F-like (56%) were observed. Most infections (87%) carried the wild type Y-allele at Pfmdr1 184 during the period of nets scale-up while during the malaria upsurges only 16% of infections had wild type and 79% of infections had mixed (mutant/wild) type. The frequency of the mixed genotypes SVMNT-like_CVMNK and SVMNT-like_CVIET within Pfcrt gene was particularly low during bednet scale up. Their frequency increased significantly (P < 0.001) during the malaria upsurges. CONCLUSION: This data demonstrated the effect of multiple interventions on the dynamics of drug resistance-associated mutations in the main malaria parasite P. falciparum in an endemic village in Senegal. Monitoring drug resistance markers should be conducted periodically to detect threats of emergence or resurgence that could compromise the efficacy of anti-malarial drugs.

A Listeria monocytogenes clone in human breast milk associated with severe acute malnutrition in West Africa: A multicentric case-controlled study.

BACKGROUND: Severe acute malnutrition (SAM) is a major public health problem affecting children under the age of five in many low- and middle-income countries, and its resolution would contribute towards achieving the several sustainable development goals. The etiology of SAM is pluri-factorial, including delayed maturation of the gut microbiota, suboptimal feeding practices and dysfunctional breastfeeding. The recent serendipitous detection of Listeria monocytogenes in the breast milk of Malian women, in contrast to French women, suggests a possible association with SAM. METHODOLOGY/ PRINCIPAL FINDINGS: To investigate the possible association of L. monocytogenes carriage in breast milk and SAM, a case-control study was performed in Senegal, with subjects recruited from two areas. Using 16S amplicon sequencing, a culture independent method, 100% (152/152) of the mothers were positive for L. monocytogenes in their breast milk while qPCR analysis gave lower recovery rates. Interestingly, after enrichment in Fraser broth and seeding on PALCALM agar, all 10 isolated strains were isolated from the milk of 10 mothers who had SAM children which also had a significantly increased relative abundance of L. monocytogenes (0.34 (SD 0.35) vs 0.05 (SD 0.07) in controls, p<0.0001). The high genomic similarity between these strains and Malian breast milk strains from a previous study supports the hypothesis of endemic clone carriage in West Africa. Moreover, the in vitro growth inhibition of L. monocytogenes using breast milk samples was obtained from only 50% of the milk of mothers who had SAM children, in contrast to control samples which systematically inhibited the growth of L. monocytogenes with a higher inhibition diameter (15.7 mm (SD 2.3) in controls versus 3.5 mm (SD 4.6) in SAM, p = 0.0001). Lactobacillus and Streptococcus isolated from the breast milk of controls inhibit L. monocytogenes in a species-dependent manner. CONCLUSIONS/SIGNIFICANCE: Our study reveals a previously unsuspected carriage of L. monocytogenes in the breast milk of West African women, which is associated with SAM. The inhibitory effect of human selected lactic acid bacterial species against L. monocytogenes might provide new therapeutic and inexpensive options to prevent and treat this neglected public health issue.

Fine-scale Spatiotemporal Mapping of Asymptomatic and Clinical Plasmodium falciparum Infections: Epidemiological Evidence for Targeted Malaria Elimination Interventions.

BACKGROUND: A detailed understanding of the contribution of the asymptomatic Plasmodium reservoir to the occurrence of clinical malaria at individual and community levels is needed to guide effective elimination interventions. This study investigated the relationship between asymptomatic Plasmodium falciparum carriage and subsequent clinical malaria episodes in the Dielmo and Ndiop villages in Senegal. METHODS: The study used a total of 2792 venous and capillary blood samples obtained from asymptomatic individuals and clinical malaria datasets collected from 2013 to 2016. Mapping, spatial clustering of infections, and risk analysis were performed using georeferenced households. RESULTS: High incidences of clinical malaria episodes were observed to occur predominantly in households of asymptomatic P falciparum carriers. A statistically significant association was found between asymptomatic carriage in a household and subsequent episode of clinical malaria occurring in that household for each individual year (P values were 0.0017, 6 × 10-5, 0.005, and 0.008 for the years 2013, 2014, 2015, and 2016 respectively) and the combined years (P = 8.5 × 10-8), which was not found at the individual level. In both villages, no significant patterns of spatial clustering of P falciparum clinical cases were found, but there was a higher risk of clinical episodes <25 m from asymptomatic individuals in Ndiop attributable to clustering within households. CONCLUSION: The findings provide strong epidemiological evidence linking the asymptomatic P falciparum reservoir to clinical malaria episodes at household scale in Dielmo and Ndiop villagers. This argues for a likely success of a mass testing and treatment intervention to move towards the elimination of malaria in the villages of Dielmo and Ndiop.

The Impact of Renewing Long-Lasting Insecticide-Treated Nets in the Event of Malaria Resurgence: Lessons from 10 Years of Net Use in Dielmo, Senegal.

The occurrence of malaria resurgences could threaten progress toward elimination of the disease. This study investigated the impact of repeated renewal of long-lasting insecticide-treated net (LLIN) universal coverage on malaria resurgence over a period of 10 years of net implementation in Dielmo (Senegal). A longitudinal study was carried out in Dielmo between August 2007 and July 2018. In July 2008, LLINs were offered to all villagers through universal campaign distribution which was renewed in July 2011, August 2014, and May 2016. Malaria cases were treated with artemisinin-based combination therapy. Two resurgences of malaria occurred during the 10 years in which LLINs have been in use. Since the third renewal of the nets, malaria decreased significantly compared with the first year the nets were implemented (adjusted incidence rate ratio) (95% CI) = 0.35 (0.15-0.85), during the ninth year after net implementation). During the tenth year of net implementation, no cases of malaria were observed among the study population. The use of nets increased significantly after the third time the nets were renewed when compared with the year after the first and the second times the nets were renewed (P < 0.001). The third renewal of nets, which took place after 2 years instead of 3 years together with a higher use of LLINs especially among the young, probably prevented the occurrence of a third malaria upsurge in this village.

The impact of daily soap use in rural areas of Senegal on respiratory infectious diseases, fevers and skin microbiota.

OBJECTIVES: Children aged <5 years are the group most affected by infectious diseases, more specifically in underdeveloped countries. A study was performed to assess the effects of daily soap use on the incidence of diarrhoea, fever, respiratory infection, and the prevalence of pathogenic bacteria on the skin. METHODS: Soap was distributed to the population of the village of Ndiop (test) for use in their daily hygiene but not to the population of the village of Dielmo (control). Fieldworkers daily recorded the clinical events in the two villages and encouraged the use of soap in Ndiop. RESULTS: A total of 638 people participated in the study. The incidence rates of cough, runny nose and fever significantly decreased in 2016 compared with 2015, unlike that of diarrhoea. In 2016, significant reductions in the incidence rates of cough, runny nose and fever were observed in children aged <15 years in Ndiop. The prevalence of Streptococcus pneumoniae, Staphylococcus aureus and Streptococcus pyogenes in the palms of the hands significantly dropped in Ndiop. CONCLUSION: Using soap reduces the incidence of respiratory infections, fevers and the prevalence of pathogenic bacteria on the skin. However, for diarrhoea, additional strategies are needed to improve outcomes.

[Thyrotoxic hypokalemic periodic paralysis in two African black women]. / Paralysie périodique hypokaliémique thyrotoxique chez deux femmes noires africaines.

Thyrotoxic hypokalemic periodic paralysis is a rare complication of hyperthyroidism. It has been most often reported in Asian subjects while it has been little described in the black population. Its mechanism has been little elucidated, but it would be caused by hyperactivity of the Na+/K+pump. We here report two cases of thyrotoxic hypokalemic periodic paralysis in black African subjects. The clinical manifestation was identical in both patients: proximal muscle paralysis of the lower limbs. Paralysis was associated with severe hypokalemia and occurred in female patients treated for Graves' disease without any other associated disease. Outcome was immediately favorable under potassium supplementation. Treatment of hyperthyroidism prevented recurrences. This study highlights the importance of suspecting the diagnosis of thyrotoxic hypokalemic periodic paralysis despite its rarity in the black African population.

Detection of Borrelia crocidurae in a vaginal swab after miscarriage, rural Senegal, Western Africa.

Tick-borne relapsing fever (TBRF) borreliae are one of the main causes of fever in rural Africa and can cause miscarriages. This article reports Borrelia crocidurae as a probable cause of spontaneous miscarriage, which was detected through vaginal self-sampling. This appears to be the first such report.

The Parathyroid carcinoma: a diagnostic challenge before surgery.

INTRODUCTION: Parathroid Carcinoma is a rare cause of primary hyperparathyroidism (PPH). His diagnosis is a real challenge. We report an observation and discuss the diagnostic guidelines before surgery. CASE: A 31-year-old Senegalese woman was admitted to our department for the exploration of diffuse bone pain and multiple pathological fractures. Physical examination revealed a right lateral mass of the neck. Serum calcium level was 142.2 mg / l and serum parathyroid hormone 42 N. Ultrasound and cervical tomodensitometry showed a parathyroid mass compressing the thyroid and trachea. The extension assessment revealed osteolytic lesions and T4-T5 epiduritis evoking metastases. Surgery and histology were performed. According to the histopathology and clinical context, the tumor was identified as a parathyroid carcinoma. CONCLUSION: The preoperative evaluation of a patient with severe hypercalcemia and high PTH levels should include the possible diagnosis of parathyroid carcinoma, especially in symptomatic patients or in case of palpable neck mass.

Feasibility, Acceptability, and Accuracy of Vaginal Self-Sampling for Screening Human Papillomavirus Types in Women from Rural Areas in Senegal.

Vaginal self-sampling and human papillomavirus (HPV) DNA testing can be useful tools for women with limited access to health care living in sub-Saharan Africa. To assess the feasibility and acceptability of vaginal self-sampling and high-risk HPV prevalence in two villages of central Senegal, women were asked to self-sample vaginal swabs for HPV detection in May, 2016. Vaginal swabs were collected from 133 women and were tested for HPV genotyping. The acceptability rate of vaginal self-sampling was 98.5%, and 99.2% of the women (133/134) used the device correctly. The quality of self-sampling was satisfactory in 100% of the samples; 10.5% of the samples were positive for HPV, including 6% with high-risk HPV types and 4% with low-risk HPV types. This preliminary study indicates that vaginal self-sampling is a valuable strategy for high-risk HPV detection and cervical cancer screening in a population of women not attending gynecologic screening in rural areas of Senegal.

Low genetic diversity and complexity of submicroscopic Plasmodium falciparum infections among febrile patients in low transmission areas in Senegal.

INTRODUCTION: Submicroscopic Plasmodium infections are common in malaria endemic countries, but very little studies have been done in Senegal. This study investigates the genetic diversity and complexity of submicroscopic P. falciparum infections among febrile patients in low transmission areas in Senegal. MATERIALS AND METHODS: Hundred and fifty blood samples were collected from febrile individuals living in Dielmo and Ndiop (Senegal) between August 2014 and January 2015, tested for microscopic and sub-microscopic P. falciparum infections and characterized for their genetic diversity and complexity of infections using msp-1 and msp-2 genotyping. RESULTS: Submicroscopic P. falciparum infections were 19.6% and 25% in Dielmo and Ndiop, respectively. K1 and 3D7 were the predominant msp-1 and msp-2 allelic types with respective frequencies of 67.36% and 67.10% in microscopic isolates and 58.24% and 78% in submicroscopic ones. Frequencies of msp-1 allelic types were statistically comparable between the studied groups (p>0.05), and were respectively 93.54% vs 87.5% for K1, 60% vs 54.83% for MAD20 and 41.93% vs 22.5% for RO33 while frequencies of msp-2 allelic types were significantly highest in the microscopy group for FC27 (41.93% vs 10%, Fisher's Exact Test, p = 0.001) and 3D7 (61.29% vs 32.5%, Fisher's Exact Test, p = 0.02). Multiplicities of infection were lowest in submicroscopic P. falciparum isolates. CONCLUSIONS: The study revealed a high submicroscopic P. falciparum carriage among patients in the study areas, and that submicroscopic P. falciparum isolates had a lower genetic diversity and complexity of malaria infections.

Another challenge in malaria elimination efforts: the increase of malaria among adults after the implementation of long-lasting insecticide-treated nets (LLINs) in Dielmo, Senegal.

BACKGROUND: The widespread use of artemisinin-based combination therapy (ACT) and long-lasting insecticide-treated nets (LLINs) has led to an impressive decrease of malaria burden these recent years in Africa. However, some new challenges about the future of malaria control and elimination efforts have appeared. Among these challenges, the loss and-or-the only partial acquisition of anti-Plasmodium immunity among exposed populations lead to an increase of the age at risk of malaria. Indeed, older children and adults may become more vulnerable to malaria. Studies about malaria among adults seemed, therefore, important. This study investigated the evolution of malaria morbidity in adults of Dielmo (Senegal) before and after the implementation of LLINs. METHODS: From August 2007 to July 2015, a longitudinal study involving adults above 15 years old was carried out in Dielmo, where ACT was introduced in June 2006 and LLINs in July 2008. In July 2011 and August 2014, all LLINs were renewed. The presence of each person in the village was monitored daily. Thick smears associated lately with rapid diagnosis test (RDT) and quantitative polymerase chain reaction methods were performed for all cases of fever. To assess malaria prevalence, thick smears and RDT were performed quarterly in all individuals. Malaria risks factors were assessed using negative binomial regression mixed-model based on person-trimester observations. RESULTS: Malaria morbidity among adults has decreased significantly since the implementation of LLINs in Dielmo. However, malaria resurgences have occurred twice during the 7 years of LLINs use. During these malaria resurgences, the overall incidence of malaria among adults was similar to the incidence during the year before the implementation of LLINs (adjusted incidence rate ratio [95% CI] aIRR = 1.04 [0.66-1.64], p = 0.88 and aIRR = 1.16 [0.74-1.80], p = 0.52 during the first and the second malaria resurgence period, respectively). Younger adults were most vulnerable during these malaria upsurges as the incidence of malaria increased significantly among them (χ2 = 5.2; p = 0.02). CONCLUSION: Malaria among adults especially younger adults should deserve more attention in the areas where malaria was previously endemic as they became vulnerable probably because of the partial acquisition and-or-the loss of anti-Plasmodium relative immunity and the non regular use of LLINs.

The Impact of Periodic Distribution Campaigns of Long-Lasting Insecticidal-Treated Bed Nets on Malaria Vector Dynamics and Human Exposure in Dielmo, Senegal.

The implementation of long-lasting insecticidal-treated bed nets (LLINs) has contributed to halving the mortality rate due to malaria since 2000 in sub-Saharan Africa. These tools are highly effective against indoor-feeding malaria vectors. Thus, to achieve the World Health Assembly's new target to reduce the burden of malaria over the next 15 years by 90%, it is necessary to understand how the spatiotemporal dynamics of malaria vectors and human exposure to bites is modified in the context of scaling up global efforts to control malaria transmission. This study was conducted in Dielmo, a Senegalese village, after the introduction of LLINs and two rounds of LLINs renewals. Data analysis showed that implementation of LLINs correlated with a significant decrease in the biting densities of the main malaria vectors, Anopheles gambiae s.l. and Anopheles funestus, reducing malaria transmission. Other environment factors likely contributed to the decrease in An. funestus, but this trend was enhanced with the introduction of LLINs. The bulk of bites occurred during sleeping hours, but the residual vector populations of An. gambiae s.l. and An. funestus had an increased propensity to bite outdoors, so a risk of infectious bites remained for LLINs users. These results highlight the need to increase the level and correct use of LLINs and to combine this intervention with complementary control measures against residual exposure, such as spatial repellents and larval source management, to achieve the goal of eliminating malaria transmission.

Investigating insecticide resistance and knock-down resistance (kdr) mutation in Dielmo, Senegal, an area under long lasting insecticidal-treated nets universal coverage for 10 years.

BACKGROUND: The use of insecticides, through indoor residual spraying and long-lasting insecticide-treated nets (LLINs), is essential to control malaria vectors. However, the sustainability of these tools is challenged by the spread of insecticide resistance in Anopheles mosquitoes. This study was conducted to assess the susceptibility to insecticides and to determine the resistance mechanisms in malaria vectors in Dielmo, a rural area of western Senegal where LLINs were introduced a decade ago. METHODS: CDC bottle bioassays were used to determine the susceptibility of 2-5 day-old unfed Anopheles gambiae s.l. females to alphacypermethrin (12.5 µg/bottle), deltamethrin (12.5 µg/bottle), etofenprox (12.5 µg/bottle), lambdacyhalothrin (12.5 µg/bottle), permethrin (21.5 µg/bottle), DDT (100 µg/bottle), bendiocarb (12.5 µg/bottle), pirimiphos-methyl (20 µg/bottle) and fenitrothion (50 µg/bottle). The involvement of glutathione-S-transferases (GSTs) in insecticide resistance was assessed using a synergist, etacrynic acid (EA, 80 µg/bottle). Polymerase chain reaction (PCR) was used to investigate the presence of 'knock-down resistance (kdr)' mutation and to identify sibling species within the An. gambiae complex. RESULTS: CDC bottle bioassays showed that mosquitoes were fully susceptible to lambdacyhalothrin, bendiocarb and fenitrothion. Overall, mortality rates of 97, 94.6, 93.5, 92.1, and 90.1% were, respectively, observed for permethrin, deltamethrin, pirimiphos-methyl, etofenprox and alphacypermethrin. Resistance to DDT was observed, with a mortality rate of 62%. The use of EA significantly improved the susceptibility of An. gambiae s.l. to DDT by inhibiting GSTs (p = 0.03). PCR revealed that Anopheles arabiensis was the predominant species (91.3%; IC 95 86.6-94%) within An. gambiae complex from Dielmo, followed by Anopheles coluzzii (5.4%; IC 95 2.7-8.1%) and Anopheles gambiae s.s. (3.3%; IC 95 0.6-5.9%). Both 1014F and 1014S alleles were found in An. arabiensis population with frequencies of 0.08 and 0.361, respectively, and 0.233 and 0.133, respectively in An. coluzzii. In An. gambiae s.s. population, only kdr L1014F mutation was detected, with a frequency of 0.167. It was observed that some individual mosquitoes carried both alleles, with 19 specimens recorded for An. arabiensis and 2 for An. coluzzii. The presence of L1014F and L1014S alleles were not associated with resistance to pyrethroids and DDT in An. arabiensis. CONCLUSIONS: The co-occurrence of 1014F and 1014S alleles and the probable involvement of GSTs enzymes in insecticide resistance in An. gambiae s.l. should prompt the local vector programme to implement non-pyrethroid/DDT insecticides alternatives.

Dramatic Changes in Malaria Population Genetic Complexity in Dielmo and Ndiop, Senegal, Revealed Using Genomic Surveillance.

Dramatic changes in transmission intensity can impact Plasmodium population diversity. Using samples from 2 distant time-points in the Dielmo/Ndiop longitudinal cohorts from Senegal, we applied a molecular barcode tool to detect changes in parasite genotypes and complexity of infection that corresponded to changes in transmission intensity. We observed a striking statistically significant difference in genetic diversity between the 2 parasite populations. Furthermore, we identified a genotype in Dielmo and Ndiop previously observed in Thiès, potentially implicating imported malaria. This genetic surveillance study validates the molecular barcode as a tool to assess parasite population diversity changes and track parasite genotypes.