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Plasmodium falciparum gametocyte kinetics and infectivity may differ between chronic and incident infections. In the current study, we assess parasite kinetics and infectivity to mosquitoes among children (aged 5–10 years) from Burkina Faso with (a) incident infections following parasite clearance ( n  = 48) and (b) chronic asymptomatic infections ( n  = 60). In the incident infection cohort, 92% (44/48) of children develop symptoms within 35 days, compared to 23% (14/60) in the chronic cohort. All individuals with chronic infection carried gametocytes or developed them during follow-up, whereas only 35% (17/48) in the incident cohort produce gametocytes before becoming symptomatic and receiving treatment. Parasite multiplication rate (PMR) and the relative abundance of ap2-g and gexp-5 transcripts are positively associated with gametocyte production. Antibody responses are higher and PMR lower in chronic infections. The presence of symptoms and sexual stage immune responses are associated with reductions in gametocyte infectivity to mosquitoes. We observe that most incident infections require treatment before the density of mature gametocytes is sufficient to infect mosquitoes. In contrast, chronic, asymptomatic infections represent a significant source of mosquito infections. Our observations support the notion that malaria transmission reduction may be expedited by enhanced case management, involving both symptom-screening and infection detection. In this longitudinal study of an incident (new infections) and chronic (asymptomatic infections) cohort of Plasmodium falciparum infection in children in Burkina Faso, the authors show higher gametocyte production and mosquito infectivity in chronic infections.

Antimalarial drugs that can block the transmission of Plasmodium gametocytes to mosquito vectors would be highly beneficial for malaria elimination efforts. Identifying transmission-blocking drugs currently relies on evaluation of their activity against gametocyte-producing laboratory parasite strains and would benefit from a testing pipeline with genetically diverse field isolates. The aims of this study were to develop a pipeline to test drugs against P . falciparum gametocyte field isolates and to evaluate the transmission-blocking activity of a set of novel compounds. Two assays were designed so they could identify both the overall transmission-blocking activity of a number of marketed and experimental drugs by direct membrane feeding assays (DMFA), and then also discriminate between those that are active against the gametocytes (gametocyte killing or sterilizing) or those that block development in the mosquito (sporontocidal). These DMFA assays used venous blood samples from naturally infected Plasmodium falciparum gametocyte carriers and locally reared Anopheles gambiae s . s . mosquitoes. Overall transmission-blocking activity was assessed following a 24 hour incubation of compound with gametocyte infected blood (TB-DMFA). Sporontocidal activity was evaluated following addition of compound directly prior to feeding, without incubation (SPORO-DMFA); Gametocyte viability was retained during 24-hour incubation at 37°C when gametocyte infected red blood cells were reconstituted in RPMI/serum. Methylene-blue, MMV693183, DDD107498, atovaquone and P218 showed potent transmission-blocking activity in the TB-DMFA, and both atovaquone and the novel antifolate P218 were potent inhibitors of sporogonic development in the SPORO-DMA. This work establishes a pipeline for the integral use of field isolates to assess the transmission-blocking capacity of antimalarial drugs to block transmission that should be validated in future studies.

Variation in biting frequency by Anopheles mosquitoes can explain some of the heterogeneity in malaria transmission in endemic areas. In this study in Burkina Faso, we assessed natural exposure to mosquitoes by matching the genotype of blood meals from 1066 mosquitoes with blood from residents of local households. We observed that the distribution of mosquito bites exceeded the Pareto rule (20/80) in two of the three surveys performed (20/85, 76, and 96) and, at its most pronounced, is estimated to have profound epidemiological consequences, inflating the basic reproduction number of malaria by 8-fold. The distribution of bites from sporozoite-positive mosquitoes followed a similar pattern, with a small number of individuals within households receiving multiple potentially infectious bites over the period of a few days. Together, our findings indicate that heterogeneity in mosquito exposure contributes considerably to heterogeneity in infection risk and suggest significant variation in malaria transmission potential.

It is currently unknown whether all Plasmodium falciparum -infected mosquitoes are equally infectious. We assessed sporogonic development using cultured gametocytes in the Netherlands and naturally circulating strains in Burkina Faso. We quantified the number of sporozoites expelled into artificial skin in relation to intact oocysts, ruptured oocysts, and residual salivary gland sporozoites. In laboratory conditions, higher total sporozoite burden was associated with shorter duration of sporogony (p<0.001). Overall, 53% (116/216) of infected Anopheles stephensi mosquitoes expelled sporozoites into artificial skin with a median of 136 expelled sporozoites (interquartile range [IQR], 34–501). There was a strong positive correlation between ruptured oocyst number and salivary gland sporozoite load (ρ = 0.8; p<0.0001) and a weaker positive correlation between salivary gland sporozoite load and number of sporozoites expelled (ρ = 0.35; p=0.0002). In Burkina Faso, Anopheles coluzzii mosquitoes were infected by natural gametocyte carriers. Among salivary gland sporozoite positive mosquitoes, 89% (33/37) expelled sporozoites with a median of 1035 expelled sporozoites (IQR, 171–2969). Again, we observed a strong correlation between ruptured oocyst number and salivary gland sporozoite load (ρ = 0.9; p<0.0001) and a positive correlation between salivary gland sporozoite load and the number of sporozoites expelled (ρ = 0.7; p<0.0001). Several mosquitoes expelled multiple parasite clones during probing. Whilst sporozoite expelling was regularly observed from mosquitoes with low infection burdens, our findings indicate that mosquito infection burden is positively associated with the number of expelled sporozoites. Future work is required to determine the direct implications of these findings for transmission potential.

Long-lasting insecticidal nets and indoor residual sprays have played a major role in significantly reducing the burden of malaria. However, the management of mosquitoes resistant to current insecticides continues to be challenging. A promising new strategy is drug-based vector control where drugs are administered to vector hosts (human/animal), which renders the host blood toxic to mosquitoes—thereby reducing mosquito lifespan, fecundity and onward transmission of pathogens. Afoxolaner, fluralaner, and lotilaner are isoxazoline derivatives widely used as systemic insecticides for ectoparasite control in companion animals. Here, the mosquitocidal activity of these compounds against Anopheles gambiae s.s, Anopheles coluzzii , Aedes aegypti , and Anopheles funestus mosquitoes was evaluated. The effect of antibiotic treatment and different carbohydrates in artificial nectar meals on isoxazoline activity was also investigated. All isoxazolines tested showed rapid killing with little difference in susceptibility between different species and genera of mosquitoes. Fluralaner showed the most potent mosquitocidal effects with IC 50 values ranging from 44 to 87 nM when mortality was assessed at 24 h post-feeding. Addition of the antibiotic cocktail or variations in sugar diet did not affect isoxazoline potency. In conclusion, data indicate potent and rapid mosquitocidal effects of isoxazolines that are likely unaffected by mosquito sugar feeding behaviour and microbiome dynamics.

Background In South-Western Burkina Faso, where malaria remains highly endemic, the widespread resistance of Anopheles mosquitoes to pyrethroid is reducing the effectiveness of insecticide-treated nets (ITNs). This study assessed 3-year trends in key entomological indicators following the deployment of standard pyrethroid-only (Interceptor®G1), dual-AI pyrethroid-chlorfenapyr (Interceptor®G2) and pyrethroid-PBO (PermaNet®3.0). Methods A longitudinal entomological study was conducted from August 2019 to February 2022 in three malaria-endemic health districts, each receiving a different ITN type. Weekly mosquito sampling was conduct in three villages per district using Human Landing Catches at two households and CDC light traps at six households. Mosquitoes were morphologically and molecularly identified, and Plasmodium falciparum infection was detected by PCR. Key indicators included mosquito density, biting behaviour, sporozoite infection rate (SIR), and entomological inoculation rate (EIR). Results A total of 73,101 female Anopheles mosquitoes were collected. The dominant vector species was An. gambiae s.l. (> 59%), with An. coluzzii prevalent in Banfora (65.5%) and An. gambiae s.s. in Gaoua (91%) and Orodara (83.3%). In Banfora, where Pyr-CFR Interceptor G2 nets were deployed, Anopheles density declined by 88.7% over the 3 years. In Gaoua (Pyr-only ITNs), mosquito density declined initially but rebounded in year 3. In Orodara (Pyr-PBO ITNs), densities remained relatively stable. Trends in SIR and EIR mirrored those in vector density, with decline in year 2 followed by resurgences in Banfora and Gaoua during year 3. Conclusion Dual-AI nets, particularly Pyr-CFR Interceptor®G2, were associated with sustained reductions in mosquito density and transmission indicators over 2 years. However, resurgence of entomological indices by the third year highlights the need for improved ITN durability and complementary vector control strategies. Continuous entomological surveillance and integrated, locally adapted interventions remain essential for sustaining malaria control in areas with high insecticide resistance.

[This corrects the article DOI: 10.1371/journal.pone.0284751.].

Background Measuring human exposure to mosquito bites is a crucial component of vector-borne disease surveillance. For malaria vectors, the human landing catch (HLC) remains the gold standard for direct estimation of exposure. This method, however, is controversial since participants risk exposure to potentially infected mosquito bites. Recently an exposure-free mosquito electrocuting trap (MET) was developed to provide a safer alternative to the HLC. Early prototypes of the MET performed well in Tanzania but have yet to be tested in West Africa, where malaria vector species composition, ecology and behaviour are different. The performance of the MET relative to HLC for characterizing mosquito vector population dynamics and biting behaviour in Burkina Faso was evaluated. Methods A longitudinal study was initiated within 12 villages in Burkina Faso in October 2016. Host-seeking mosquitoes were sampled monthly using HLC and MET collections over 14 months. Collections were made at 4 households on each night, with METs deployed inside and outside at 2 houses, and HLC inside and outside at another two. Malaria vector abundance, species composition, sporozoite rate and location of biting (indoor versus outdoor) were recorded. Results In total, 41,800 mosquitoes were collected over 324 sampling nights, with the major malaria vector being Anopheles gambiae sensu lato (s.l.) complex. Overall the MET caught fewer An. gambiae s.l. than the HLC (mean predicted number of 0.78 versus 1.82 indoors, and 1.05 versus 2.04 outdoors). However, MET collections gave a consistent representation of seasonal dynamics in vector populations, species composition, biting behaviour (location and time) and malaria infection rates relative to HLC. As the relative performance of the MET was somewhat higher in outdoor versus indoor settings, this trapping method slightly underestimated the proportion of bites preventable by LLINs compared to the HLC (MET = 82.08%; HLC = 87.19%). Conclusions The MET collected proportionately fewer mosquitoes than the HLC. However, estimates of An. gambiae s.l. density in METs were highly correlated with HLC. Thus, although less sensitive, the MET is a safer alternative than the HLC. Its use is recommended particularly for sampling vectors in outdoor environments where it is most sensitive.

Background The introduction of next-generation insecticide-treated nets (ITNs) in Burkina Faso aims to mitigate pyrethroid resistance in malaria vectors. This study evaluated the impact of different ITN types on phenotypic resistance and kdr mutation frequencies in Anopheles gambiae sensus lacto (s.l.) populations across three health districts over 3 years. Methods Annual mosquito collections were conducted in Banfora (where pyrethroid–chlorfenapyr nets had been distributed), Gaoua (pyrethroid-only ITNs) and Orodara (pyrethroid–piperonyl butoxide [PBO] ITNs). Two populations were analysed: adult females collected directly from the field and those reared from field-collected larvae. World Health Organization (WHO) susceptibility bioassays measured 24-h mortality after exposure to 1×, 5× and 10× concentrations of deltamethrin and alphacypermethrin, with and without pre-exposure to piperonyl butoxide. Frequencies of kdr mutations L995F and L995S were determined by polymerase chain reaction (PCR). Results High-intensity resistance was observed in each study district, with mortality consistently below 45% and not reaching WHO thresholds even at 10× doses. PBO increased mortality, indicating metabolic resistance, but failed to restore full susceptibility. L995F predominated across all districts, years and mosquito populations. L995S remained low and variable. Pyr-only nets were associated with rising L995F frequencies and lower mortality in resistance assays. Pyrethroid (Pyr)–chlorfenapyr (CFR) nets improved mortality in resistance assays without increasing kdr prevalence. Pyr–PBO nets showed partial and inconsistent efficacy, with mosquitoes having mixed patterns in resistance assays. Similar patterns between field and laboratory-reared populations were observed. Conclusions ITN type strongly influenced resistance dynamics. Dual-active ingredient (AI) nets, particularly Pyr–CFR, appear more effective in managing resistance. Integrated resistance management combining ITN rotation, routine monitoring and complementary interventions is essential to preserve vector control efficacy. Graphical abstract

Background Aedes aegypti , the primary vector of Dengue fever in Burkina Faso, breeds in a variety of domestic and peri-domestic water holding containers. The influence of these water containers on the mosquitoes’ ability to survive exposure to chemical insecticides remains unclear. This study investigated the insecticide susceptibility profile of Aedes aegypti in relation to larval habitat types in three districts of Ouagadougou. Methods Adult females reared from larvae collected in “domestic containers” and “car tires” were exposed separately to papers impregnated with deltamethrin, pirimiphos-methyl, and bendiocarb to determine their susceptibility profiles. A subsample of mosquitoes per locality and container type was screened for the F1534C, V1016I and V410L kdr mutations involved in pyrethroid resistance. Results Mosquito population from the three localities showed high resistance to deltamethrin and pirimiphos-methyl and moderate resistance to bendiocarbe, with mortality rates ranging from 15% to 27%, 21% to 33% and 67% to 86%, respectively. Mosquitoes from the \"domestic containers\" were significantly more resistant to deltamethrin than those from tires (10% vs. 22%, p  < 0.002). The frequency of the 1534C mutation was also significantly higher in the \"domestic containers\" compared to those from tires (0.88 vs. 0.76, p  = 0.013).The other mutations 1016I and 410L, were reported with an overall frequency of 0.51 and 0.36, respectively. Conclusions These findings suggest that larval habitat type may influence both the level and mechanisms of resistance in Aedes aegypti . This has important implications for the design of targeted vector control strategies in dengue-endemic settings.