Abstract Background Over the last decades, Plasmodium falciparum – the main causative agent of malaria – has constantly developed resistance to antimalarial drugs such as chloroquine, sulfadoxine-pyrimethamine or artemisinin derivatives. Therefore, active surveillance in the ex vivo susceptibility to the antimalarial drugs used as partner drugs in artemisinin-based combination therapies (the current frontline antimalarial) such as amodiaquine, lumefantrine or piperaquine, is essential. Methods Here, we evaluated the ex vivo susceptibility, expressed with the ex vivo SYBR™ Green, to six antimalarial drugs (amodiaquine, chloroquine, lumefantrine, mefloquine, piperaquine and quinine) from 34 P. falciparum isolates collected in 2018 in Thiès (Senegal). Whole-genome sequencing (WGS) was used to search for mutations in P. falciparum genes known to be associated with drug resistance. Results P. falciparum isolates showed reduced ex vivo susceptibility only to chloroquine (16% of the isolates). Mutations in pfcrt K76T (21%) and pfmdr1 Y184F (53%) were the most prevalent. A significant correlation was observed between the mutants pfcrt 76T and pfmdr1 184F and IC50 values for chloroquine. A significant decrease in ex vivo susceptibility to chloroquine and quinine associated with the pfcrt R371I was also detected (P < 0.001). Conclusion Our results suggest that the ex vivo susceptibility of P. falciparum isolates to amodiaquine, lumefantrine, mefloquine, piperaquine and quinine remains high in Thiès. Directly measuring ex vivo parasite drug response and sequencing resistance mutations overtime are both useful tools for monitoring parasite drug response in field samples.

Abstract Background Over the last decades, Plasmodium falciparum – the main causative agent of malaria – has constantly developed resistance to antimalarial drugs such as chloroquine, sulfadoxine-pyrimethamine or artemisinin derivatives. Therefore, active surveillance in the ex vivo susceptibility to the antimalarial drugs used as partner drugs in artemisinin-based combination therapies (the current frontline antimalarial) such as amodiaquine, lumefantrine or piperaquine, is essential. Methods Here, we evaluated the ex vivo susceptibility, expressed with the ex vivo SYBR™ Green, to six antimalarial drugs (amodiaquine, chloroquine, lumefantrine, mefloquine, piperaquine and quinine) from 34 P. falciparum isolates collected in 2018 in Thiès (Senegal). Whole-genome sequencing (WGS) was used to search for mutations in P. falciparum genes known to be associated with drug resistance. Results P. falciparum isolates showed reduced ex vivo susceptibility only to chloroquine (16% of the isolates). Mutations in pfcrt K76T (21%) and pfmdr1 Y184F (53%) were the most prevalent. A significant correlation was observed between the mutants pfcrt 76T and pfmdr1 184F and IC 50 values for chloroquine. A significant decrease in ex vivo susceptibility to chloroquine and quinine associated with the pfcrt R371I was also detected ( P < 0.001) . Conclusion Our results suggest that the ex vivo susceptibility of P. falciparum isolates to amodiaquine, lumefantrine, mefloquine, piperaquine and quinine remains high in Thiès. Directly measuring ex vivo parasite drug response and sequencing resistance mutations overtime are both useful tools for monitoring parasite drug response in field samples.

Background Malaria control is highly dependent on the effectiveness of artemisinin-based combination therapy (ACT), the current frontline malaria curative treatment. Unfortunately, the emergence and spread of parasites resistant to artemisinin (ART) derivatives in Southeast Asia and South America, and more recently in Rwanda and Uganda (East Africa), compromise their long-term use in sub-Saharan Africa, where most malaria deaths occur. Methods Here, ex vivo susceptibility to dihydroartemisinin (DHA) was evaluated from 38 Plasmodium falciparum isolates collected in 2017 in Thiès (Senegal) expressed in the Ring-stage Survival Assay (RSA). Both major and minor variants were explored in the three conserved-encoding domains of the pfkelch13 gene, the main determinant of ART resistance using a targeted-amplicon deep sequencing (TADS) approach. Results All samples tested in the ex vivo RSA were found to be susceptible to DHA (parasite survival rate < 1%). The non-synonymous mutations K189T and K248R in pfkelch13 were observed each in one isolate, as major (99%) or minor (5%) variants, respectively. Conclusion The results suggest that ART is still fully effective in the Thiès region of Senegal in 2017. Investigations combining ex vivo RSA and TADS are a useful approach for monitoring ART resistance in Africa.

Background Malaria control and elimination strategies are based on levels of transmission that are usually determined by data collected from health facilities. In endemic areas, asymptomatic Plasmodium infection is thought to represent the majority of infections, though they are not diagnosed nor treated. Therefore, there might be an underestimation of the malaria reservoir, resulting in inadequate control strategies. In addition, these untreated asymptomatic Plasmodium infections maintain transmission, making it difficult or impossible to reach malaria elimination goals. Thus, the aim of this study was to determine the prevalence of asymptomatic Plasmodium infections in southeastern Senegal. Methods A cross sectional study was conducted among asymptomatic individuals (N = 122) living in the village of Andiel located in Bandafassi, Kédougou, which consisted of about 200 inhabitants during the malaria transmission season in late October 2019. For each individual without malaria-related symptoms and who consented to participate, a rapid diagnostic test (RDT) was performed in the field. Results were confirmed in the laboratory with photo-induced electron transfer (PET-PCR). Results Malaria prevalence was 70.3% by PET-PCR and 41.8% by RDT. During the same period, the health post of the area reported 49. 1% test positivity rate by RDT. The majority of the infected study population, 92.9%, was infected with a single species and 7.1% had two or three species of Plasmodium . Plasmodium falciparum was predominant and represented 90.2% of the infections, while 6.5% were due to Plasmodium ovale and 3.3% to Plasmodium malariae . 59.4% of children targeted for SMC (zero to ten years old) were infected. Conclusion In southeastern Senegal, where the transmission is the highest, malaria control strategies should address asymptomatic Plasmodium infections at the community level. The results suggest that this area could be eligible for mass drug administration. Moreover, non-falciparum species could be more common and its prevalence should be determined countrywide.

Background : Malaria control and elimination strategies are based on levels of transmission that are usually determined by data collected from health facilities. In endemic areas, asymptomatic malaria is thought to represent the majority of infections and is therefore not diagnosed nor treated. As a consequence, they are missed when analyzing data due to the lack of visiting the health facilities unless they are sick. Therefore, there might be an underestimation of the malaria prevalence resulting in inadequate control strategies. In addition, these untreated asymptomatic cases maintain transmission making it difficult or impossible to reach malaria elimination goals. Thus, the aim of this study was to determine the prevalence of asymptomatic malaria in southeastern Senegal. Methods : A cross sectional study was conducted among asymptomatic individuals (N = 122) living in the village of Andiel located in Bandafassi, Kedougou which consisting of about 200 inhabitants during the malaria transmission season in late October 2019. For each individual without malaria symptoms and who consented to participate in the study, a rapid diagnosis test (RDT) was performed in the field. Results were confirmed in the laboratory with nested PCR and photo-induced electron transfer (PET-PCR). Results : Malaria prevalence was 70.25% with PET-PCR, 41.80% with RDT and 41.32% based on the nested PCR. The majority of the study population; 92.94% was infected with a single species (mono-infection) and 7.06% had two or three species of Plasmodium . P. falciparum was predominant and represented 90.22% of the infections, while 6.52% were due to P. ovale and 3.26% to P. malariae . RDT detected more malaria cases than nested PCR among children and in individuals aged fifteen years and older; PET-PCR detected more cases (64.70%) than nested PCR (62%) and RDT (52.94%) in this age group. Conclusion : Asymptomatic infection is a threat to malaria elimination. In southeastern Senegal, where the transmission is the highest in the country, malaria control strategies should address asymptomatic cases at the community level. This high prevalence of asymptomatic malaria observed suggests that this area is eligible for mass drug administration. Moreover, non-falciparum species could be more common and its prevalence should be determined countrywide.