Malian adults maintain serologic responses to virulent PfEMP1s amid seasonal patterns of fluctuation

Plasmodium falciparum erythrocyte membrane protein-1s (PfEMP1s), diverse malaria proteins expressed on the infected erythrocyte surface, play an important role in pathogenesis, mediating adhesion to host vascular endothelium. Antibodies to particular non-CD36-binding PfEMP1s are associated with protection against severe disease. We hypothesized that given lifelong P. falciparum exposure, Malian adults would have broad PfEMP1 serorecognition and high seroreactivity levels during follow-up, particularly to non-CD36-binding PfEMP1s such as those that attach to endothelial protein C receptor (EPCR) and intercellular adhesion molecule-1 (ICAM-1). Using a protein microarray, we determined serologic responses to 166 reference PfEMP1 fragments during a dry and subsequent malaria transmission season in Malian adults. Malian adult sera had PfEMP1 serologic responses throughout the year, with decreased reactivity to a small subset of PfEMP1 fragments during the dry season and increases in reactivity to a different subset of PfEMP1 fragments during the subsequent peak malaria transmission season, especially for intracellular PfEMP1 domains. For some individuals, PfEMP1 serologic responses increased after the dry season, suggesting antigenic switching during asymptomatic infection. Adults were more likely to experience variable serorecognition of CD36-binding PfEMP1s than non-CD36-binding PfEMP1s that bind EPCR or ICAM-1, which remained serorecognized throughout the year. Sustained seroreactivity to non-CD36-binding PfEMP1s throughout adulthood amid seasonal fluctuation patterns may reflect underlying protective severe malaria immunity and merits further investigation.

Malaria and dengue in Hodeidah city, Yemen: High proportion of febrile outpatients with dengue or malaria, but low proportion co-infected

Background The emergence of dengue in malaria-endemic countries with limited diagnostic resources, such as Yemen, can be problematic because presumptive treatment of febrile cases as being malaria is a common practice. Co-infections with dengue and malaria are often overlooked and misdiagnosed as being a mono-infection because of clinical similarities. In Hodeidah city, Yemen, the capacity to conduct the diagnosis can be aggravated by the war context. To assess the magnitude of the problem, we determined the proportions of malaria, dengue and co-infection in relation to clinical characteristics among febrile outpatients. Methods This cross-sectional study included 355 febrile outpatients from Hodeidah city during the malaria transmission season (September 2018 –February 2019). Sociodemographic and clinical characteristics were collected using a pre-designed, structured questionnaire. Malaria was confirmed using microscopy and rapid diagnostic tests (RDTs), while dengue was confirmed using RDTs. Results Mono-infection proportions of 32.4% for falciparum malaria and 35.2% for dengue were found, where about two-thirds of dengue patients had a recent probable infection. However, co-infection with falciparum malaria and dengue was detected among 4.8% of cases. There was no statistically significant difference between having co-infection and mono-infection with malaria or dengue in relation to the sociodemographic characteristics. On the other hand, the odds of co-infection were significantly lower than the odds of malaria among patients presenting with sweating (OR = 0.1, 95% CI: 0.05–0.45; p <0.001), while the odds of co-infection were 3.5 times significantly higher than the odds of dengue among patients presenting with vomiting (OR = 3.5, 95% CI: 1.20–10.04; p <0.021). However, there were no statistically significant differences between having co-infection and mono-infection (malaria or dengue) in relation to other clinical characteristics. Conclusions Mono-infection with malaria or dengue can be detected among about one-third of febrile outpatients in Hodeidah, while almost 5.0% of cases can be co-infected. Sociodemographic and clinical characteristics cannot easily distinguish malaria patients from dengue-infected or co-infected ones, reinforcing the necessity of laboratory confirmation and avoidance of treating febrile patients as being presumed malaria cases.

Nutritional status in young children prior to the malaria transmission season in Burkina Faso and Mali, and its impact on the incidence of clinical malaria

Background Malaria and malnutrition remain major problems in Sahel countries, especially in young children. The direct effect of malnutrition on malaria remains poorly understood, and may have important implications for malaria control. In this study, nutritional status and the association between malnutrition and subsequent incidence of symptomatic malaria were examined in children in Burkina Faso and Mali who received either azithromycin or placebo, alongside seasonal malaria chemoprevention. Methods Mid-upper arm circumference (MUAC) was measured in all 20,185 children who attended a screening visit prior to the malaria transmission season in 2015. Prior to the 2016 malaria season, weight, height and MUAC were measured among 4149 randomly selected children. Height-for-age, weight-for-age, weight-for-height, and MUAC-for-age were calculated as indicators of nutritional status. Malaria incidence was measured during the following rainy seasons. Multivariable random effects Poisson models were created for each nutritional indicator to study the effect of malnutrition on clinical malaria incidence for each country. Results In both 2015 and 2016, nutritional status prior to the malaria season was poor. The most prevalent form of malnutrition in Burkina Faso was being underweight (30.5%; 95% CI 28.6–32.6), whereas in Mali stunting was most prevalent (27.5%; 95% CI 25.6–29.5). In 2016, clinical malaria incidence was 675 per 1000 person-years (95% CI 613–744) in Burkina Faso, and 1245 per 1000 person-years (95% CI 1152–1347) in Mali. There was some evidence that severe stunting was associated with lower incidence of malaria in Mali (RR 0.81; 95% CI 0.64–1.02; p = 0.08), but this association was not seen in Burkina Faso. Being moderately underweight tended to be associated with higher incidence of clinical malaria in Burkina Faso (RR 1.27; 95% CI 0.98–1.64; p = 0.07), while this was the case in Mali for moderate wasting (RR 1.27; 95% CI 0.98–1.64; p = 0.07). However, these associations were not observed in severely affected children, nor consistent between countries. MUAC-for-age was not associated with malaria risk. Conclusions Both malnutrition and malaria were common in the study areas, high despite high coverage of seasonal malaria chemoprevention and long-lasting insecticidal nets. However, no strong or consistent evidence was found for an association between any of the nutritional indicators and the subsequent incidence of clinical malaria.

Selection of pfcrt K76 and pfmdr1 N86 Coding Alleles after Uncomplicated Malaria Treatment by Artemether-Lumefantrine in Mali

Background: Artemether-lumefantrine is a highly effective artemisinin-based combination therapy that was adopted in Mali as first-line treatment for uncomplicated Plasmodium falciparum malaria. This study was designed to measure the efficacy of artemether-lumefantrine and to assess the selection of the P. falciparum chloroquine resistance transporter (pfcrt) and P. falciparum multi-drug resistance 1 (pfmdr1) genotypes that have been associated with drug resistance. Methods: A 28-day follow-up efficacy trial of artemether-lumefantrine was conducted in patients aged 6 months and older suffering from uncomplicated falciparum malaria in four different Malian areas during the 2009 malaria transmission season. The polymorphic genetic markers MSP2, MSP1, and Ca1 were used to distinguish between recrudescence and reinfection. Reinfection and recrudescence were then grouped as recurrent infections and analyzed together by PCR-restriction fragment length polymorphism (RFLP) to identify candidate markers for artemether-lumefantrine tolerance in the P. falciparum chloroquine resistance transporter (pfcrt) gene and the P. falciparum multi-drug resistance 1 (pfmdr1) gene. Results: Clinical outcomes in 326 patients (96.7%) were analyzed and the 28-day uncorrected adequate clinical and parasitological response (ACPR) rate was 73.9%. The total PCR-corrected 28-day ACPR was 97.2%. The pfcrt 76T and pfmdr1 86Y population prevalence decreased from 49.3% and 11.0% at baseline (n = 337) to 38.8% and 0% in patients with recurrent infection (n = 85); p = 0.001), respectively. Conclusion: Parasite populations exposed to artemether-lumefantrine in this study were selected toward chloroquine-sensitivity and showed a promising trend that may warrant future targeted reintroduction of chloroquine or/and amodiaquine.

High prevalence of asymptomatic Plasmodium infection in Bandafassi, South-East Senegal

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.

Effect of 4 years of seasonal malaria chemoprevention on the acquisition of antibodies to Plasmodium falciparum antigens in Ouelessebougou, Mali

Background More than 200 million people live in areas of highly seasonal malaria transmission where Seasonal Malaria Chemoprevention (SMC) with sulfadoxine-pyrimethamine (SP) and amodiaquine (AQ) was recommended in 2012 by WHO. This strategy is now implemented widely and protected more than 19 million children in 2018. It was previously reported that exposure to SMC reduced antibody levels to AMA1, MSP-142 and CSP, but the duration of exposure to SMC up to three 3 years, had no effect on antibody levels to MSP-142 and CSP. Methods In 2017, a cross-sectional survey was carried out 1 month after the last dose of SMC had been given to children aged 4–5 years randomly selected from areas where SMC had been given for 2 or 4 years during the malaria transmission season. A total of 461 children were enrolled, 242 children in areas where SMC had been implemented for 4 years and 219 children in areas where SMC had been implemented for 2 years. Antibody extracted from dry blood spots was used to measure IgG levels to the malaria antigens CSP, MSP-142 and AMA1 by ELISA. Results The prevalence of antibodies to MSP-142 was similar in children who had received SMC for 4 years compared to those who had received SMC for only 2 years (85.1 vs 86.0%, ajusted odd ratio (aOR) = 1.06, 95% confidence intervals (CI 0.62–1.80), p = 0.80). The prevalence of antibodies to AMA-1 and to CSP was not lower in children who received SMC for 4 years compared to those who had received SMC for only 2 years (95.3 vs 88.8%, aOR = 3.16, 95% CI 1.44–6.95, p = 0.004 for AMA-1; and 91.2 vs 81.9%, aOR = 3.14, 95% CI 1.70–5.76, p < 0.001 for CSP). Median antibody levels for anti-MSP-142 IgG were not significatively inferior in children who had received SMC for four rather than 2 years (0.88 (IQR: 0.64–1.15) and 0.95 ((0.68–1.15), respectively), anti-CSP (1.30 (1.00–1.56) and 1.17 (0.87–1.47)), and anti-AMA-1 (1.45 (1.24–1.68) and 1.41 (1.17–1.64)). Conclusion In an area of high seasonal malaria transmission, children who had received SMC for 4 years did not had lower seropositivity or antibody levels to AMA1, MSP-142 and CSP compared to children who had received SMC for only 2 years suggesting that children who have received SMC for 4 years may not be more at risk of malaria after the cessation of SMC than children who have received SMC for a shorter period.

Gametocyte clearance in children, from western Kenya, with uncomplicated Plasmodium falciparum malaria after artemether–lumefantrine or dihydroartemisinin–piperaquine treatment

Background The efficacy and safety of artemether–lumefantrine (AL) and dihydroartemisinin–piperaquine (DP) against asexual parasites population has been documented. However, the effect of these anti-malarials on sexual parasites is still less clear. Gametocyte clearance following treatment is essential for malaria control and elimination efforts; therefore, the study sought to determine trends in gametocyte clearance after AL or DP treatment in children from a malaria-endemic site in Kenya. Methods Children aged between 0.5 and 12 years from Busia, western Kenya with uncomplicated Plasmodium falciparum malaria were assigned randomly to AL or DP treatment. A total of 334 children were enrolled, and dried blood spot samples were collected for up to 6 weeks after treatment during the peak malaria transmission season in 2016 and preserved. Plasmodium falciparum gametocytes were detected by qRT-PCR and gametocyte prevalence, density and mean duration of gametocyte carriage were determined. Results At baseline, all the 334 children had positive asexual parasites by microscopy, 12% (40/334) had detectable gametocyte by microscopy, and 83.7% (253/302) children had gametocytes by RT-qPCR. Gametocyte prevalence by RT-qPCR decreased from 85.1% (126/148) at day 0 to 7.04% (5/71) at day 42 in AL group and from 82.4% (127/154) at day 0 to 14.5% (11/74) at day 42 in DP group. The average duration of gametocyte carriage as estimated by qRT-PCR was slightly shorter in the AL group (4.5 days) than in the DP group (5.1 days) but not significantly different (p = 0.301). Conclusion The study identifies no significant difference between AL and DP in gametocyte clearance. Gametocytes persisted up to 42 days post treatment in minority of individuals in both treatment arms. A gametocytocidal drug, in combination with artemisinin-based combination therapy, will be useful in blocking malaria transmission more efficiently.

Differential contribution of Anopheles coustani and Anopheles arabiensis to the transmission of Plasmodium falciparum and Plasmodium vivax in two neighboring villages of Madagascar

BackgroundMalaria is still a heavy public health concern in Madagascar. Few studies combining parasitology and entomology have been recently conducted despite the need for such information to design proper vector control measures. In a region of moderate to intense transmission of both Plasmodium falciparum and Plasmodium vivax, we conducted a combined parasitology and entomology survey in two nearby villages, across a malaria transmission season from December 2016 to April 2017.Methodology/Principal findingsCommunity-based surveys were conducted in the two close by villages at three time points during a single malaria transmission season. Plasmodium carriage in the human populations was determined by Rapid Diagnostic Tests (RDTs), microscopy and real-time PCR. Anthropophilic mosquitoes were captured by human landing captures and presence of Plasmodium sporozoites was assessed by robust Real Time PCR. Overall human malaria prevalence was 8.0% by RDT, 4.8% by microscopy and 11.9% by PCR, mainly due to P. falciparum detected in 92.2% of the PCR positive samples and Plasmodium vivax (5.7%). No significant differences in Plasmodium human carriage was observed between the 2 villages at any time point. Of the 1553 anopheline mosquitoes tested, 13 were found carrying Plasmodium sporozoites, the majority of them being captured outdoor. The mosquito sporozoite indices were not significantly different between the two villages. However, our entomological analysis revealed that Anopheles coustani was the main vector in one village, being responsible of 25.5 infective bites during the whole survey, whereas it was Anopheles arabiensis in the other village with 15 infective bites. In addition, we found a significant higher number of endophagic An. coustani and An. arabiensis in one village compared to the other.Conclusions/SignificanceDespite similar human malaria prevalence in two close by villages, the entomological survey demonstrated the contribution of two different mosquito species in each village, and importantly the role of a suspected secondary malaria vector, An. coustani, as the main vector in one village. This, along with its higher endophagic rate in that village, highlights the importance of combining parasitology and entomology surveys for better targeting the actual local malaria vector. Such study should contribute to the malaria pre-elimination goal established under the 2018-2022 National Malaria Strategic Plan.Author SummaryMalaria is still a major health concern in many countries in sub-Saharan Africa such as Madagascar. In this study, we determined the contribution of malaria vectors in the transmission of Plasmodium parasites in two nearby villages in an area of moderate to high malaria transmission in Madagascar. We collected, during a single malaria transmission season, parasitological data in the human population and entomological data in the mosquito population, in order to evaluate Plasmodium carriage in these two populations. The results showed that despite similarity in human malaria prevalence and in vector species diversity in each village, the contribution of vectors was different between the two villages. An. arabiensis was the major vector in Ambohitromby while it was An. coustani that played this role in Miarinarivo. Importantly, this study is the first that clearly demonstrates that An. coustani could act as a major local vector in Madagascar. Such study should help deploying adapted malaria vector control and contributing to the malaria pre-elimination goal established under the 2018-2022 National Malaria Strategic Plan.