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.

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.

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.

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.

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.

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.

[Serological survey of animal toxoplasmosis in Senegal]. / Enquête de séroprévalence de la toxoplasmose animale au Sénégal.

Toxoplasma gondii is an obligate, intracellular, parasitic protozoan within the phylum Apicomplexa that causes toxoplasmosis in mammalian hosts (including humans) and birds. We used modified direct agglutination test for the screening of the animals' sera collected in Senegal. In total, 419 animals' sera have been studied: 103 bovines, 43 sheep, 52 goats, 63 horses, 13 donkeys and 145 dogs. The collection of sera was performed in four different regions of Senegal: Dakar, Sine Saloum, Kedougou and Basse Casamance from 2011 to 2013. We have revealed antibodies in 13% of bovines, 16% of sheep, 15% of goats, 30% of horses, 23% of donkeys and 67% of dogs. Private dogs from villages were more often to have the anti-Toxoplasma antibodies compared to security society-owned dogs from Dakar. It may be explained by different meal consumed by dogs (factory-produced meal for dogs from Dakar vs. irregular sources for village dogs). Intense circulation of T. gondii in the studied zone may explain the unusually high seroprevalence among horses and donkeys. Tropical climate with high temperature and humidity is favorable for the conservation of oocysts of T. gondii. Results presented here may contribute to the evaluation of the risks of toxoplasmosis in humans in Senegal.