Multiplicity of Plasmodium falciparum infection in asymptomatic children in Senegal: relation to transmission, age and erythrocyte variants

Plasmodium falciparum infection status in children less than 10 years old under seasonal malaria chemoprevention and risk of clinical malaria in the Koulikoro health district, Mali

Introduction

Seasonal malaria chemoprevention (SMC) with Sulfadoxine pyrimethamine plus amodiaquine (SP + AQ) consist of a monthly administration of therapeutic dose to children under five years of age during the high risk of malaria in area where malaria is highly seasonal. According to SMC recommendation, both non-infected and asymptomatic Plasmodium falciparum infected children will receive similar treatment. The gap in our knowledge is how the effect of asymptomatic infection on the efficacy of SMC in preventing clinical malaria over a four-week period. Thus, this study aimed to assess the risk of clinical malaria and its association with children's infection status when SMC treatment is given.

Methodology

The study was carried out in the Koulikoro health district in Mali and concerned children under 10 years of age. A total of 726 and 1452 children were randomly selected and followed over the SMC campaign in the years 2019 and 2020 respectively. Prevalence of asymptomatic P. falciparum infection was determined each round by microscopy before SMC drugs intake. Children were passively followed over a four-week period to determine incidence of clinical malaria. R-Studio software was used for analysis. The risk of clinical malaria by infection status was estimated using a logistic regression. A Kaplan-Meier curve was used to determine the survival time between infected and uninfected children. The Pearson Chi-square test was used to compare proportions with the significant level at p< 0.05.

Results

The average prevalence of asymptomatic infection was 11.0% both years, and it was higher among children aged 5 to 9 years old in 2019 (p<0.001) and 2020 (p=0.016). The risk of clinical malaria was significantly higher among asymptomatic infected children 2019: (RR=3.05, CI [2.04-4.72]) and 2020 (RR=1.43, CI [1.04-1.97]) transmission seasons. Likewise, the time of the first malaria occurrence was statistically lower among infected children regardless the year (p<0.001 in 2019 and p=0.01 in 2020).

Conclusion

Results show a high risk of clinical malaria in asymptomatic infected children during SMC delivery. Screening for P. falciparum infection before the SMC treatment could significantly enhance the impact of the strategy on malaria morbidity in endemic areas.

Asymptomatic malaria and predictors among migrant farmworkers East Shewa zone Oromia Ethiopia

Asymptomatic malaria can impact existing malaria control and elimination efforts around the world, particularly in Africa, where the majority of malaria cases and death occurs. This is a cross-sectional study aimed to determine the prevalence and predictors of asymptomatic malaria among migrant farmworkers from June to July 2020 in the Upper Awash Agro-industry, East Shewa zone, Oromia Regional State, Ethiopia. A total of 254 migrant farmworkers without signs and symptoms of malaria were enrolled. Data on socio-demographic characteristics and malaria prevention practices were obtained through a structured questionnaire. Venous blood samples were collected and diagnosed using microscopy, rapid diagnostic tests, and polymerase chain reaction (PCR). Data were coded, entered, and analyzed using SPSS version-21 statistical software. Multivariable logistic regression was used to assess associated factors. A p < 0.05 was considered statistically significant. The overall prevalence of asymptomatic malaria among farmworkers in this study was 5.1% [95% CI 1.6, 6.7]. The proportions of Plasmodium falciparum was 90.0% (9/10) while it was 10.0% (1/10) for Plasmodium vivax. Out of the microscopy and/or RDT-confirmed malaria cases, (n = 9; 100%) were confirmed to be P. falciparum by nested PCR, while (n = 3/122; 2.46%) were found to be P. falciparum among 50% negative cases with the microscopy and/or RDT. The gametocyte stage was detected in 40% of microscopically positive cases out of which 44.4% belongs to P. falciparum. Home area/origin of migrant laborers [AOR = 6.08, (95% CI 1.08, 34.66)], family history of malaria [AOR = 8.15, (95% CI 1.43, 46.44)], and outdoor sleeping [AOR = 10.14, (95% CI 1.15, 89.14)] were significantly associated with asymptomatic malaria. In conclusion, asymptomatic malaria was detected among farmworkers in the study area and it was significantly associated with outdoor sleeping, home area, and family history of malaria. Prevention tools and control strategies, particularly focusing on migrant farmworkers, should be considered to support the ongoing malaria control and elimination effort in Ethiopia.

Genomics reveals heterogeneous Plasmodium falciparum transmission and selection signals in Zambia

BACKGROUND

Genomic surveillance is crucial for monitoring malaria transmission and understanding parasite adaptation to interventions. Zambia lacks prior nationwide efforts in malaria genomic surveillance among African countries.

METHODS

We conducted genomic surveillance of Plasmodium falciparum parasites from the 2018 Malaria Indicator Survey in Zambia, a nationally representative household survey of children under five years of age. We whole-genome sequenced and analyzed 241 P. falciparum genomes from regions with varying levels of malaria transmission across Zambia and estimated genetic metrics that are informative about transmission intensity, genetic relatedness between parasites, and selection.

RESULTS

We provide genomic evidence of widespread within-host polygenomic infections, regardless of epidemiological characteristics, underscoring the extensive and ongoing endemic malaria transmission in Zambia. Our analysis reveals country-level clustering of parasites from Zambia and neighboring regions, with distinct separation in West Africa. Within Zambia, identity by descent (IBD) relatedness analysis uncovers local spatial clustering and rare cases of long-distance sharing of closely related parasite pairs. Genomic regions with large shared IBD segments and strong positive selection signatures implicate genes involved in sulfadoxine-pyrimethamine and artemisinin combination therapies drug resistance, but no signature related to chloroquine resistance. Furthermore, differences in selection signatures, including drug resistance loci, are observed between eastern and western Zambian parasite populations, suggesting variable transmission intensity and ongoing drug pressure.

CONCLUSIONS

Our findings enhance our understanding of nationwide P. falciparum transmission in Zambia, establishing a baseline for analyzing parasite genetic metrics as they vary over time and space. These insights highlight the urgency of strengthening malaria control programs and surveillance of antimalarial drug resistance.

Genomics reveals heterogeneous Plasmodium falciparum transmission and population differentiation in Zambia and bordering countries

Genomic surveillance plays a critical role in monitoring malaria transmission and understanding how the parasite adapts in response to interventions. We conducted genomic surveillance of malaria by sequencing 241 Plasmodium falciparum genomes from regions with varying levels of malaria transmission across Zambia. We found genomic evidence of high levels of within-host polygenomic infections, regardless of epidemiological characteristics, underscoring the extensive and ongoing endemic malaria transmission in the country. We identified country-level clustering of parasites from Zambia and neighboring countries, and distinct clustering of parasites from West Africa. Within Zambia, our identity by descent (IBD) relatedness analysis uncovered spatial clustering of closely related parasite pairs at the local level and rare cases of long-distance sharing. Genomic regions with large shared IBD segments and strong positive selection signatures identified genes involved in sulfadoxine-pyrimethamine and artemisinin combination therapies drug resistance, but no signature related to chloroquine resistance. Together, our findings enhance our understanding of P. falciparum transmission nationwide in Zambia and highlight the urgency of strengthening malaria control programs and surveillance of antimalarial drug resistance.

Plasmodium falciparum msp-1 and msp-2 genetic diversity and multiplicity of infection in isolates from Congolese patients in the Republic of Congo

With limited up to date data from the Republic of Congo, the aim of this study was to investigate allelic polymorphism of merozoite surface protein-1 (msp-1) and merozoite surface protein-2 (msp-2). This will help assess the genetic diversity and multiplicity of Plasmodium falciparum infection (MOI), from uncomplicated malaria individuals living in Brazzaville. Between March and October 2021, a cross-sectional study was carried out at a health center in Madibou District located in the south of Brazzaville. Plasmodium infection was diagnosed in human blood by microscopy and the block 2 of P. falciparum msp-1 and block 3 of msp-2 genes were genotyped by nested PCR. Overall, 57 genotypes with fragment sizes ranging from 110 to 410 bp were recorded for msp-1, among which 25, 21, and 11 genotypes identified for K1, MAD20, and RO33 allelic families respectively. RO33 (34.3%) and MAD20 (34.3%) allelic families were more frequent compared to K1 (31.4%) although the difference was not statistically significant. Also, 47 msp-2 genotypes were identified, including 26 FC27 genotypes type, and 21 genotypes belonging to the 3D7 allelic family. FC27 was more frequent (52.3%) compared to 3D7 (47.7%). The prevalence of the polyclonal infection was 90.0% while the MOI was 2.90 ± 1.0. The MOI and polyclonal infection were not significantly associated with the parasitaemia and anaemia. This study reveals a high genetic diversity and the trend of increasing MOI of P. falciparum isolates from the south of Brazzaville, compared to the reports from the same setting before the COVID-19 pandemic.

The diversity of Plasmodium falciparum isolates from asymptomatic and symptomatic school-age children in Kinshasa Province, Democratic Republic of Congo

BACKGROUND

Understanding Plasmodium falciparum population diversity and transmission dynamics provides information on the intensity of malaria transmission, which is needed for assessing malaria control interventions. This study aimed to determine P. falciparum allelic diversity and multiplicity of infection (MOI) among asymptomatic and symptomatic school-age children in Kinshasa Province, Democratic Republic of Congo (DRC).

METHODS

A total of 438 DNA samples (248 asymptomatic and 190 symptomatic) were characterized by nested PCR and genotyping the polymorphic regions of pfmsp1 block 2 and pfmsp2 block 3.

RESULTS

Nine allele types were observed in pfmsp1 block2. The K1-type allele was predominant with 78% (229/293) prevalence, followed by the MAD20-type allele (52%, 152/293) and RO33-type allele (44%, 129/293). Twelve alleles were detected in pfmsp2, and the 3D7-type allele was the most frequent with 84% (256/304) prevalence, followed by the FC27-type allele (66%, 201/304). Polyclonal infections were detected in 63% (95% CI 56, 69) of the samples, and the MOI (SD) was 1.99 (0.97) in P. falciparum single-species infections. MOIs significantly increased in P. falciparum isolates from symptomatic parasite carriers compared with asymptomatic carriers (2.24 versus 1.69, adjusted b: 0.36, (95% CI 0.01, 0.72), p = 0.046) and parasitaemia > 10,000 parasites/µL compared to parasitaemia < 5000 parasites/µL (2.68 versus 1.63, adjusted b: 0.89, (95% CI 0.46, 1.25), p < 0.001).

CONCLUSION

This survey showed low allelic diversity and MOI of P. falciparum, which reflects a moderate intensity of malaria transmission in the study areas. MOIs were more likely to be common in symptomatic infections and increased with the parasitaemia level. Further studies in different transmission zones are needed to understand the epidemiology and parasite complexity in the DRC.

Plasmodium falciparum Merozoite Surface Proteins Polymorphisms and Treatment Outcomes among Patients with Uncomplicated Malaria in Mwanza, Tanzania

Background. The severity of malaria infection depends on the host, parasite and environmental factors. Merozoite surface protein (msp) diversity determines transmission dynamics, P. falciparum immunity evasion, and pathogenesis or virulence. There is limited updated information on P. falciparum msp polymorphisms and their impact on artemether-lumefantrine treatment outcomes in Tanzania. Therefore, this study is aimed at examining msp genetic diversity and multiplicity of infection (MOI) among P. falciparum malaria patients. The influence of MOI on peripheral parasite clearance and adequate clinical and parasitological response (ACPR) was also assessed. Methods. Parasite DNA was extracted from dried blood spots according to the manufacture’s protocol. Primary and nested PCR were performed. The PCR products for both the block 2 region of msp1 and the block 3 regions of msp2 genes and their specific allelic families were visualized on a 2.5% agarose gel. Results. The majority of the isolates, 58/102 (58.8%) for msp1 and 69/115 (60.1%) for msp2, harboured more than one parasite genotypes. For the msp1 gene, K1 was the predominant allele observed (75.64%), whereas RO33 occurred at the lowest frequency (43.6%). For the msp2 gene, the 3D7 allele was observed at a higher frequency (81.7%) than the FC27 allele (76.9%). The MOIs were 2.44 for msp1 and 2.27 for msp2 ( $p=0.669$ ). A significant correlation between age and multiplicity of infection (MOI) for msp1 or MOI for msp2 was not established in this study (rho = 0.074, $p=0.521$ and rho = −0.129, $p=0.261$ , respectively). Similarly, there was no positive correlation between parasite density at day 1 and MOI for both msp1 (rho = 0.113, $p=0.244$ ) and msp2 (rho = 0.043, $p=0.712$ ). The association between MOI and ACPR was not observed for either msp1 or mps2 ( $p=0.776$ and 0.296, respectively). Conclusions. This study reports high polyclonal infections, MOI and allelic frequencies for both msp1 and msp2. There was a lack of correlation between MOI and ACPR. However, a borderline significant correlation was observed between day 2 parasitaemia and MOI.

Prospective surveillance study to detect antimalarial drug resistance, gene deletions of diagnostic relevance and genetic diversity of Plasmodium falciparum in Mozambique: protocol

INTRODUCTION

Genomic data constitute a valuable adjunct to routine surveillance that can guide programmatic decisions to reduce the burden of infectious diseases. However, genomic capacities remain low in Africa. This study aims to operationalise a functional malaria molecular surveillance system in Mozambique for guiding malaria control and elimination.

METHODS AND ANALYSES

This prospective surveillance study seeks to generate Plasmodium falciparum genetic data to (1) monitor molecular markers of drug resistance and deletions in rapid diagnostic test targets; (2) characterise transmission sources in low transmission settings and (3) quantify transmission levels and the effectiveness of antimalarial interventions. The study will take place across 19 districts in nine provinces (Maputo city, Maputo, Gaza, Inhambane, Niassa, Manica, Nampula, Zambézia and Sofala) which span a range of transmission strata, geographies and malaria intervention types. Dried blood spot samples and rapid diagnostic tests will be collected across the study districts in 2022 and 2023 through a combination of dense (all malaria clinical cases) and targeted (a selection of malaria clinical cases) sampling. Pregnant women attending their first antenatal care visit will also be included to assess their value for molecular surveillance. We will use a multiplex amplicon-based next-generation sequencing approach targeting informative single nucleotide polymorphisms, gene deletions and microhaplotypes. Genetic data will be incorporated into epidemiological and transmission models to identify the most informative relationship between genetic features, sources of malaria transmission and programmatic effectiveness of new malaria interventions. Strategic genomic information will be ultimately integrated into the national malaria information and surveillance system to improve the use of the genetic information for programmatic decision-making.

ETHICS AND DISSEMINATION

The protocol was reviewed and approved by the institutional (CISM) and national ethics committees of Mozambique (Comité Nacional de Bioética para Saúde) and Spain (Hospital Clinic of Barcelona). Project results will be presented to all stakeholders and published in open-access journals.

TRIAL REGISTRATION NUMBER

NCT05306067.

It Is Time to Strengthen the Malaria Control Policy of the Democratic Republic of Congo and Include Schools and School-Age Children in Malaria Control Measures

Despite a decade of sustained malaria control, malaria remains a serious public health problem in the Democratic Republic of Congo (DRC). Children under five years of age and school-age children aged 5–15 years remain at high risk of symptomatic and asymptomatic malaria infections. The World Health Organization’s malaria control, elimination, and eradication recommendations are still only partially implemented in DRC. For better malaria control and eventual elimination, the integration of all individuals into the national malaria control programme will strengthen malaria control and elimination strategies in the country. Thus, inclusion of schools and school-age children in DRC malaria control interventions is needed.

Genomic miscellany and allelic frequencies of Plasmodium falciparum msp-1, msp-2 and glurp in parasite isolates

Introduction

The genomic miscellany of malaria parasites can help inform the intensity of malaria transmission and identify potential deficiencies in malaria control programs. This study was aimed at investigating the genomic miscellany, allele frequencies, and MOI of P. falciparum infection.

Methods

A total of 85 P. falciparum confirmed isolates out of 100 were included in this study that were collected from P. falciparum patients aged 4 months to 60 years in nine districts of Khyber Pakhtunkhwa Province. Parasite DNA was extracted from 200µL whole blood samples using the Qiagen DNA extraction kit following the manufacturer’s instructions. The polymorphic regions of msp-1, msp-2 and glurp loci were genotyped using nested PCR followed by gel electrophoresis for amplified fragments identification and subsequent data analysis.

Results

Out of 85 P. falciparum infections detected, 30 were msp-1 and 32 were msp-2 alleles specific. Successful amplification occurred in 88.23% (75/85) isolates for msp-1, 78.9% (67/85) for msp-2 and 70% (60/85) for glurp gene. In msp-1, the K1 allelic family was predominantly prevalent as 66.66% (50/75), followed by RO33 and MAD20. The frequency of samples with single infection having only K1, MAD20 and RO33 were 21.34% (16/75), 8% (6/75), and 10.67% (8/75), respectively. In msp-2, both the FC27 and 3D7 allelic families revealed almost the same frequencies as 70.14% (47/67) and 67.16% (45/67), respectively. Nine glurp RII region alleles were identified in 60 isolates. The overall mean multiplicity of infection for msp genes was 1.6 with 1.8 for msp-1 and 1.4 for msp-2, while for glurp the MOI was 1.03. There was no significant association between multiplicity of infection and age groups (Spearman’s rank coefficient = 0.050; P = 0.6) while MOI and parasite density correlated for only msp-2 allelic marker.

Conclusions

The study showed high genetic diversity and allelic frequency with multiple clones of msp-1, msp-2 and glurp in P. falciparum isolates in Khyber Pakhtunkhwa, Pakistan. In the present study the genotype data may provide valuable information essential for monitoring the impact of malaria eradication efforts in this region.

Prevalence and risk of Plasmodium vivax infection among Duffy-negative individuals: a systematic review and meta-analysis

A better understanding of the occurrence and risk of Plasmodium vivax infection among Duffy-negative individuals is required to guide further research on these infections across Africa. To address this, we used a meta-analysis approach to investigate the prevalence of P. vivax infection among Duffy-negative individuals and assessed the risk of infection in these individuals when compared with Duffy-positive individuals. This study was registered with The International Prospective Register of Systematic Reviews website (ID: CRD42021240202) and followed Preferred Reporting Items for Systematic review and Meta-Analyses guidelines. Literature searches were conducted using medical subject headings to retrieve relevant studies in Medline, Web of Science, and Scopus, from February 22, 2021 to January 31, 2022. Selected studies were methodologically evaluated using the Joanna Briggs Institute (JBI) Critical Appraisal Tools to assess the quality of cross-sectional, case–control, and cohort studies. The pooled prevalence of P. vivax infection among Duffy-negative individuals and the odds ratio (OR) of infection among these individuals when compared with Duffy-positive individuals was estimated using a random-effects model. Results from individual studies were represented in forest plots. Heterogeneity among studies was assessed using Cochrane Q and I² statistics. We also performed subgroup analysis of patient demographics and other relevant variables. Publication bias among studies was assessed using funnel plot asymmetry and the Egger’s test. Of 1593 retrieved articles, 27 met eligibility criteria and were included for analysis. Of these, 24 (88.9%) reported P. vivax infection among Duffy-negative individuals in Africa, including Cameroon, Ethiopia, Sudan, Botswana, Nigeria, Madagascar, Angola, Benin, Kenya, Mali, Mauritania, Democratic Republic of the Congo, and Senegal; while three reported occurrences in South America (Brazil) and Asia (Iran). Among studies, 11 reported that all P. vivax infection cases occurred in Duffy-negative individuals (100%). Also, a meta-analysis on 14 studies showed that the pooled prevalence of P. vivax infection among Duffy-negative individuals was 25% (95% confidence interval (CI) − 3%–53%, I² = 99.96%). A meta-analysis of 11 studies demonstrated a decreased odds of P. vivax infection among Duffy-negative individuals (p = 0.009, pooled OR 0.46, 95% CI 0.26–0.82, I² = 80.8%). We confirmed that P. vivax infected Duffy-negative individuals over a wide prevalence range from 0 to 100% depending on geographical area. Future investigations on P. vivax infection in these individuals must determine if Duffy-negativity remains a protective factor for P. vivax infection.

Plasmodium falciparum msp1 and msp2 genetic diversity in parasites isolated from symptomatic and asymptomatic malaria subjects in the South of Benin

Symptomatic and asymptomatic malaria patients are considered as the reservoirs of human Plasmodium. In the present study, we have evaluated the Plasmodium falciparum merozoite surface protein-1 (Pfmsp1) and protein-2 (Pfmsp2) genetic diversity among the symptomatic and asymptomatic malaria infection from health facilities in Cotonou, Benin Republic. A cross-sectional study recruited 158 individuals, including 77 from the asymptomatic and 81 from the symptomatic groups. The parasites were genotyped using Nested Polymerase Chain Reaction. Samples identified as Plasmodium falciparum were genotyped for their genetic diversity. No significant difference was observed in the overall multiplicity of infection (MOI) between the asymptomatic and symptomatic groups. In the symptomatic group, the overall frequency of K1, MAD20, and RO33 allelic family was more predominant (98.5%) followed by 3D7 (87.3%) and FC27 (83.1%). However, in asymptomatic group, the K1 alleles were the most prevalent (100%) followed by FC27 (89.9%), 3D7 (76.8%), MAD20 (60.5%), and RO33 (35.5%). The frequency of multiple allelic types (K1+MAD20+RO33) at the Pfmsp1 loci in the symptomatic infections was significantly higher when compared to that of the asymptomatic ones (97% vs. 34%, p < 0.05), whereas no difference was observed in the frequency of multiple allelic types (3D7 and FC27) at the Pfmsp2 loci between the two groups. The high presence of msp1 multiple infections in the symptomatic group compared to asymptomatic ones suggests an association between the genetic diversity and the onset of malaria symptoms. These data can provide valuable information in the development of a vaccine that could reduce the symptomatic disease.

Plasmodium vivax From Duffy-Negative and Duffy-Positive Individuals Share Similar Gene Pools in East Africa

Plasmodium vivax malaria was thought to be rare in Africa, but an increasing number of P. vivax cases reported across Africa and in Duffy-negative individuals challenges this dogma. The genetic characteristics of P. vivax in Duffy-negative infections, the transmission of P. vivax in East Africa, and the impact of environments on transmission remain largely unknown. This study examined genetic and transmission features of P. vivax from 107 Duffy-negative and 305 Duffy-positive individuals in Ethiopia and Sudan. No clear genetic differentiation was found in P. vivax between the 2 Duffy groups, indicating between-host transmission. P. vivax from Ethiopia and Sudan showed similar genetic clusters, except samples from Khartoum, possibly due to distance and road density that inhibited parasite gene flow. This study is the first to show that P. vivax can transmit to and from Duffy-negative individuals and provides critical insights into the spread of P. vivax in sub-Saharan Africa.

Malaria parasite species composition of Plasmodium infections among asymptomatic and symptomatic school-age children in rural and urban areas of Kinshasa, Democratic Republic of Congo

BACKGROUND

Malaria remains a major public health concern in the Democratic Republic of Congo (DRC), and school-age children are relatively neglected in malaria prevalence surveys and may constitute a significant reservoir of transmission. This study aimed to understand the burden of malaria infections in school-age children in Kinshasa/DRC.

METHODS

A total of 634 (427 asymptomatic and 207 symptomatic) blood samples collected from school-age children aged 6 to 14 years were analysed by microscopy, RDT and Nested-PCR.

RESULTS

The overall prevalence of Plasmodium spp. by microscopy, RDT and PCR was 33%, 42% and 62% among asymptomatic children and 59%, 64% and 95% in symptomatic children, respectively. The prevalence of Plasmodium falciparum, Plasmodium malariae and Plasmodium ovale spp. by PCR was 58%, 20% and 11% among asymptomatic and 93%, 13% and 16% in symptomatic children, respectively. Among P. ovale spp., P. ovale curtisi, P. ovale wallikeri and mixed P. ovale curtisi + P. ovale wallikeri accounted for 75%, 24% and 1% of infections, respectively. All Plasmodium species infections were significantly more prevalent in the rural area compared to the urban area in asymptomatic infections (p < 0.001). Living in a rural as opposed to an urban area was associated with a five-fold greater risk of asymptomatic malaria parasite carriage (p < 0.001). Amongst asymptomatic malaria parasite carriers, 43% and 16% of children harboured mixed Plasmodium with P. falciparum infections in the rural and the urban areas, respectively, whereas in symptomatic malaria infections, it was 22% and 26%, respectively. Few children carried single infections of P. malariae (2.2%) and P. ovale spp. (1.9%).

CONCLUSION

School-age children are at significant risk from both asymptomatic and symptomatic malaria infections. Continuous systematic screening and treatment of school-age children in high-transmission settings is needed.

Similar Ferroportin Q248H polymorphism prevalence in patients with Plasmodium falciparum malaria and control subjects in the low-endemic setting of Botswana

INTRODUCTION

Recent evidence suggests that ferroportin (FPN) Q248H may confer a survival advantage against malaria by reducing erythrocytic intracellular iron in Africans. We investigated if FPN Q248H mutation, that is prevalent in Batswana, is a factor in limiting the susceptibility to Plasmodium falciparum malaria.

METHODS

264 archived dried blood spot samples (183 P. falciparum malaria cases and 81 controls, matched for geographical region and season for equal exposure) were genotyped. Human and P. falciparum DNA was extracted using Chelex-100 resin and P. falciparum molecular confirmation performed. Ferroportin Q248H mutation was identified by restriction fragment length polymorphism. The prevalence of the FPN Q248H mutation and allele frequency and the accompanying 95% confidence interval were calculated. A qPCR method was employed to estimate P. falciparum parasitaemia. Association between FPN and malaria susceptibility was tested using Pearson Chi-square test and Mood's median test was used to compare P. falciparum parasitaemias according to FPN Q248H mutation.

RESULTS

All samples were successfully genotyped. The FPN Q248H allele frequency was 0.08 (95% CI: 0.05-0.11) in cases and 0.08 (95% CI: 0.02-0.14) in controls, consistent with Hardy-Weinberg equilibrium. The prevalence of FPN Q248H phenotype was comparable in patients with P. falciparum malaria and in un-infected individuals, 16.4% (95% CI: 11.0-21.8) vs 14.8% (95% CI: 7.1-22.5), P = 0.746. In addition, no association of presence of FPN Q248H with reduced parasitaemia was recorded, P = 0.837.

CONCLUSION

In this small study, FPN Q248H polymorphism prevalence was comparable between patients with P. falciparum malaria and control subjects in the low-endemic setting of Botswana.

Allelic diversity of merozoite surface protein genes (msp1 and msp2) and clinical manifestations of Plasmodium falciparum malaria cases in Aceh, Indonesia

BACKGROUND

The malaria control programme in Indonesia has successfully brought down malaria incidence in many parts in Indonesia, including Aceh Province. Clinical manifestation of reported malaria cases in Aceh varied widely from asymptomatic, mild uncomplicated to severe and fatal complications. The present study aims to explore the allelic diversity of merozoite surface protein 1 gene (msp1) and msp2 among the Plasmodium falciparum isolates in Aceh Province and to determine their potential correlation with the severity of malaria clinical manifestation.

METHODS

Screening of over 500 malaria cases admitted to the hospitals in 11 districts hospital within Aceh Province during 2013-2015, identified 90 cases of P. falciparum mono-infection without any co-morbidity. The subjects were clinically phenotyped and parasite DNA was extracted and polymerase chain reaction (PCR) amplified for the msp1 and msp2 allelic subfamilies.

RESULTS

Analysis of clinical manifestation revealed that fever-chill is the most frequent symptom. Based on WHO criteria showed 19 cases were classified as severe and 71 as mild malaria. Analysis of msp1 gene revealed the presence of K1 allele subfamily in 34 subjects, MAD20 in 42 subjects, RO33 in 1 subject, and mixed allelic of K1 + MAD20 in 5 subjects, K1 + RO33 in 4 subjects, and MAD20 + RO33 in 4 subjects. Analysis of msp2 gene revealed 34 subjects carried the FC27 allelic subfamily, 37 subjects carried the 3D7 and 19 subjects carried the mixed FC27 + 3D7. Analysis of multiplicity of infection revealed that msp1 alleles is slightly higher than msp2 with the mean of MOI were 2.69 and 2.27, respectively. Statistical analysis to determine the association between each clinical manifestation and msp1 and msp2 alleles revealed that liver function abnormal value was associated with the msp2 mixed alleles (odds ratio (OR):0.13; 95%CI: 0.03-0.53). Mixed msp1 of K1 + RO33 was associated with severe malaria (OR: 28.50; 95%CI: 1.59-1532.30).

CONCLUSION

This study found a strong association between severe malaria in Aceh with subjects carrying the msp1 mixed alleles of K1 and RO33. The liver function abnormal value associated with the msp2 mixed allelic subfamilies. Further study in different geographic areas is recommended.

Genetic polymorphisms of Plasmodium falciparum isolates from Melka-Werer, North East Ethiopia based on the merozoite surface protein-2 (msp-2) gene as a molecular marker

Background

The characterization of parasite populations circulating in malaria endemic areas is necessary to evaluate the success of ongoing interventions and malaria control strategies. This study was designed to investigate the genetic diversity of Plasmodium falciparum isolates from the semi-arid area in North East Ethiopia, using the highly polymorphic merozoite surface protein-2 (msp2) gene as a molecular marker.

Methods

Dried blood spot isolates were collected from patients with P. falciparum infection between September 2014 and January 2015 from Melka-Werer, North East Ethiopia. Parasite DNA was extracted and genotyped using allele-specific nested polymerase chain reactions for msp2.

Results

52 isolates were collected with msp2 identified in 41 (78.8%) isolates. Allele typing of the msp2 gene detected the 3D7/IC allelic family in 54% and FC27 allelic family in 46%. A total of 14 different msp2 genotypes were detected including 6 belonging to the 3D7/IC family and 8 to the FC27 family. Forty percent of isolates had multiple genotypes and the overall mean multiplicity of infections (MOI) was 1.2 (95%CI 0.96–1.42). The heterozygosity index was 0.50 for the msp2 locus. There was no difference in MOI between age groups. A negative correlation between parasite density and multiplicity of infection was found (p = 0.02).

Conclusion

Plasmodium falciparum isolates from the semi-arid area of North East Ethiopia are mainly monoclonal with low MOI and limited genetic diversity in the study population.

Multiplicity of Asymptomatic Plasmodium falciparum Infections and Risk of Clinical Malaria: A Systematic Review and Pooled Analysis of Individual Participant Data

BACKGROUND

The malaria parasite Plasmodium falciparum holds an extensive genetic polymorphism. In this pooled analysis, we investigate how the multiplicity in asymptomatic P. falciparum infections-that is, the number of coinfecting clones-affects the subsequent risk of clinical malaria in populations living under different levels of transmission.

METHODS

A systematic search of the literature was performed to identify studies in which P. falciparum infections were genotyped in asymptomatic individuals who were followed up prospectively regarding the incidence of clinical malaria. Individual participant data were pooled from 15 studies (n = 3736 individuals).

RESULTS

Multiclonal asymptomatic infections were associated with a somewhat increased subsequent risk of clinical malaria in the youngest children, followed by an initial declining risk with age irrespective of transmission intensity. At approximately 5 years of age, the risk continued the gradual decline with age in high-transmission settings. However, in older children in moderate-, low-, and seasonal-transmission settings, multiclonal infections were either not significantly associated with the risk of subsequent febrile malaria or were associated with an increased risk.

CONCLUSIONS

The number of clones in asymptomatic P. falciparum infections is associated with different risks of subsequent clinical malaria depending on age and transmission intensity.

Genetic diversity and complexity of Plasmodium falciparum infections in the microenvironment among siblings of the same household in North-Central Nigeria

Background

Plasmodium falciparum parasites are known to exhibit extensive genetic diversity in areas of high transmission intensity and infected individuals in such communities often harbour several complex mixtures of parasite clones with different genetic characteristics. However, in the micro-environment, the extent of genetic diversity of P. falciparum parasites remain largely unknown. In this study therefore, the complexity of P. falciparum infections in households was investigated among symptomatic siblings, living under the same roof in north-central Nigeria.

Methods

Children were enrolled into the study if they were at least two from a household and presented with symptoms of uncomplicated malaria. Clinical malaria was confirmed by light microscopy of Giemsa-stained thick and thin blood films. Genomic DNA was isolated from blood spots on filter paper. Molecular characterization of P. falciparum isolates was done by allele-specific nested PCR of the highly polymorphic merozoite surface protein-2 (msp-2) gene.

Results

Ninety-three children from 43 households were enrolled into this study. A total of 26 different msp-2 alleles were identified from 215 fragments (range: 180–480 bp). Majority of the isolates [65.6% (n = 61)] were polyclonal infections consisting of 2–6 clones and were significantly more common with the FC27 allelic family (p = 0.036). The multiplicity of infection (MOI) per household ranged from 1.0 to 4.5 while the overall MOI in the study population was 2.31. The pattern of distribution of msp-2 allele types among the households fell into two categories: households where both msp-2 allele types (FC27 and 3D7) were present; households where only one msp-2 allele type (FC27 or 3D7) was present. Majority of the households [88.4% (n = 38)], had both msp-2 allele types but they were disproportionately distributed among the children while in a few households [11.6% (n = 5)], all the children were infected with only one type of msp-2 allele.

Conclusion

These findings showed that P. falciparum isolates exhibit remarkable degree of genetic diversity in the micro-environment and are composed mainly of multiclonal infections, which is an indication of a high ongoing parasite transmission. This suggests that the micro-environment is an important area of focus for malaria control interventions and for evaluating intervention programmes.

Determinants of Plasmodium falciparum multiplicity of infection and genetic diversity in Burkina Faso

BACKGROUND

Investigating malaria transmission dynamics is essential to inform policy decision making. Whether multiplicity of infection (MOI) dynamic from individual infections could be a reliable malaria metric in high transmission settings with marked variation in seasons of malaria transmission has been poorly assessed. This study aimed at investigating factors driving Plasmodium falciparum MOI and genetic diversity in a hyperendemic area of Burkina Faso.

METHODS

Blood samples collected from a pharmacovigilance trial were used for polymerase chain reaction genotyping of the merozoite surface proteins 1 and 2. MOI was defined as the number of distinct parasite genotypes co-existing within a particular infection. Monthly rainfall data were obtained from satellite data of the Global Precipitation Measurement Database while monthly malaria incidence aggregated data were extracted from District Health Information Software 2 medical data of the Center-West health regional direction.

RESULTS

In the study area, infected people harboured an average of 2.732 (± 0.056) different parasite genotypes. A significant correlation between the monthly MOI and the monthly malaria incidence was observed, suggesting that MOI could be a good predictor of transmission intensity. A strong effect of season on MOI was observed, with infected patients harbouring higher number of parasite genotypes during the rainy season as compared to the dry season. There was a negative relationship between MOI and host age. In addition, MOI decreased with increasing parasite densities, suggesting that there was a within-host competition among co-infecting genetically distinct P. falciparum variants. Each allelic family of the msp1 and msp2 genes was present all year round with no significant monthly fluctuation.

CONCLUSIONS

In high malaria endemic settings with marked variation in seasons of malaria transmission, MOI represents an appropriate malaria metric which provides useful information about the longitudinal changes in malaria transmission in a given area. Besides transmission season, patient age and parasite density are important factors to consider for better understanding of variations in MOI. All allelic families of msp1 and msp2 genes were found in both dry and rainy season. The approach offers the opportunity of translating genotyping data into relevant epidemiological information for malaria control.

Investigating selected host and parasite factors potentially impacting upon seasonal malaria chemoprevention in Bama, Burkina Faso

BACKGROUND

Since 2014, seasonal malaria chemoprevention (SMC) with amodiaquine-sulfadoxine-pyrimethamine (AQ-SP) has been implemented on a large scale during the high malaria transmission season in Burkina Faso. This paper reports the prevalence of microscopic and submicroscopic malaria infection at the outset and after the first round of SMC in children under 5 years old in Bama, Burkina Faso, as well as host and parasite factors involved in mediating the efficacy and tolerability of SMC.

METHODS

Two sequential cross-sectional surveys were conducted in late July and August 2017 during the first month of SMC in a rural area in southwest Burkina Faso. Blood smears and dried blood spots were collected from 106 to 93 children under five, respectively, at the start of SMC and again 3 weeks later. Malaria infection was detected by microscopy and by PCR from dried blood spots. For all children, day 7 plasma concentrations of desethylamodiaquine (DEAQ) were measured and CYP2C8 genetic variants influencing AQ metabolism were genotyped. Samples were additionally genotyped for pfcrt K76T and pfmdr1 N86Y, molecular markers associated with reduced amodiaquine susceptibility.

RESULTS

2.8% (3/106) of children were positive for Plasmodium falciparum infection by microscopy and 13.2% (14/106) by nested PCR within 2 days of SMC administration. Three weeks after SMC administration, in the same households, 4.3% (4/93) of samples were positive by microscopy and 14.0% (13/93) by PCR (p = 0.0007). CYP2C8*2, associated with impaired amodiaquine metabolism, was common with an allelic frequency of 17.1% (95% CI  10.0-24.2). Day 7 concentration of DEAQ ranged from 0.48 to 362.80 ng/mL with a median concentration of 56.34 ng/mL. Pfmdr1 N86 predominated at both time points, whilst a non-significant trend towards a higher prevalence of pfcrt 76T was seen at week 3.

CONCLUSION

This study showed a moderate prevalence of low-level malaria parasitaemia in children 3 weeks following SMC during the first month of administration. Day 7 concentrations of the active DEAQ metabolite varied widely, likely reflecting variability in adherence and possibly metabolism. These findings highlight factors that may contribute to the effectiveness of SMC in children in a high transmission setting.

Asymptomatic carriage of Plasmodium falciparum by individuals with variant blood groups and haemoglobin genotypes in southern Ghana

Background

The ABO and the Rhesus blood group systems, as well as various abnormal haemoglobin (Hb) variants (haemoglobinopathies) are known to influence malaria parasite carriage and disease severity in individuals living in malaria endemic areas. This study identified the blood group and Hb variant distribution and Plasmodium falciparum infection status of afebrile individuals living in southern Ghana.

Methods

Afebrile participants were recruited from Obom (358) in the Greater Accra Region and Ewim (100) and Simiw (329) in the Central Region of Ghana. Venous blood (1 ml) was collected into EDTA vacutainer tubes. Three 20 μl drops of blood were used for blood group analysis using the tile method. Another 500 μl aliquot was used for the qualitative sickling test using sodium metabisulphite and haemoglobin electrophoresis. Genomic DNA was extracted from 100 μl of whole blood and used in P. falciparum species-specific PCR.

Results

The most abundant blood group and abnormal haemoglobin variant in both sites was blood group O + (47.4%) and HbAS (15.8%). A total of 13 (1.7%) of the participants had full haemoglobinopathies (SS, SC and CC), whilst 196 (25.4%) were carriers (AS and AC). Although there was a significantly higher prevalence of sickling positive participants from the Central Region, genotyping identified a similar prevalence of each of the abnormal haemoglobin genes in both sites. Asymptomatic parasite carriage estimated by PCR was 40.9% in the Central Region and 41.8% in the Greater Accra Region.

Conclusions

Asymptomatic carriage of P. falciparum parasite in the study population was not associated with any particular blood group variant or haemoglobin genotype.

Variation of prevalence of malaria, parasite density and the multiplicity of Plasmodium falciparum infection throughout the year at three different health centers in Brazzaville, Republic of Congo

Background

In the Republic of Congo, hot temperature and seasons distortions observed may impact the development of malaria parasites. We investigate the variation of malaria cases, parasite density and the multiplicity of Plasmodium falciparum infection throughout the year in Brazzaville.

Methods

From May 2015 to May 2016, suspected patients with uncomplicated malaria were enrolled at the Hôpital de Mfilou, CSI « Maman Mboualé», and the Laboratoire National de Santé Publique. For each patient, thick blood was examined and parasite density was calculated. After DNA isolation, MSP1 and MSP2 genes were genotyped.

Results

A total of 416, 259 and 131 patients with suspected malaria were enrolled at the CSI «Maman Mboualé», Hôpital de Mfilou and the Laboratoire National de Santé Publique respectively. Proportion of malaria cases and geometric mean parasite density were higher at the CSI «Maman Mboualé» compared to over sites (P-value <0.001). However the multiplicity of infection was higher at the Hôpital de Mfilou (P-value <0.001).

At the Laboratoire National de Santé Publique, malaria cases and multiplicity of infection were not influenced by different seasons. However, variation of the mean parasite density was statistically significant (P-value <0.01).

Higher proportions of malaria cases were found at the end of main rainy season either the beginning of the main dry season at the Hôpital de Mfilou and the CSI «Maman Mboualé»; while, lowest proportions were observed in September and January and in September and March respectively. Higher mean parasite densities were found at the end of rainy seasons with persistence at the beginning of dry seasons. The lowest mean parasite densities were found during dry seasons, with persistence at the beginning of rainy seasons. Fluctuation of the multiplicity of infection throughout the year was observed without significance between seasons.

Conclusion

The current study suggests that malaria transmission is still variable between the north and south parts of Brazzaville. Seasonal fluctuations of malaria cases and mean parasite densities were observed with some extension to different seasons. Thus, both meteorological and entomological studies are needed to update the season’s periods as well as malaria transmission intensity in Brazzaville.

Genetic diversity of Plasmodium falciparum isolates from patients with uncomplicated and severe malaria based on msp-1 and msp-2 genes in Gublak, North West Ethiopia

BACKGROUND

Malaria infection can present with a wide variety of symptoms, ranging from mild to severe. Plasmodium falciparum isolates in uncomplicated and severe malaria infections may have different parasite genetic profiles. This study was conducted to assess differences in genetic diversity and allelic frequencies in P. falciparum isolates according to malaria severity and age of patients in the Gublack area, northwest Ethiopia.

METHODS

Cross-sectional health facility-based study conducted in Gublak, Ethiopia between July, 2017 and October, 2017. Symptomatic P. falciparum malaria patients with microscopically-confirmed infection were enrolled. Parasite DNA was extracted from filter paper blood spots and the polymorphic regions of the msp-1 and msp-2 genes were genotyped using allele-specific nested-PCR with fragment analysis by gel electrophoresis.

RESULTS

A total of 118 patients were enrolled including 95 (80.5%) with uncomplicated infection and 23 (19.5%) with severe disease. In msp-1, the K1 allelic family was similarly prevalent in uncomplicated 42 (44.2%) and severe disease 12 (52.2%). In msp-2, FC27 was detected in 55 (57.9%) of uncomplicated infections and IC/3D7 in 14 (60.9%) of severe infections. 76 (64.4%) of the 118 isolates contained multiple genotypes; 56 (58.9%) in uncomplicated infections and 19 (82.6%) in severe infections. The overall of multiplicity of infection was 2.2 (95% CI 1.98-2.42) with 1.4 (95% CI 1.23-1.55) and 1.7 (95% CI 1.49-1.86) for msp-1 and msp-2, respectively. Multiplicity of infection was significantly higher in severe than uncomplicated infections (3.0 (95% CI 2.61-3.47) versus 2.0 (95% CI 1.83-2.23), respectively, p = 0.001). There was no difference in multiplicity of infection across age groups (p = 0.104).

CONCLUSION

Patients with severe malaria were more likely to have multiclonal infections. Further studies are needed to describe the association between P. falciparum genotypes and malaria severity in different malaria transmission areas.

Molecular Surveillance of Plasmodium falciparum Drug Resistance Markers in Clinical Samples from Botswana

Drug-resistant Plasmodium falciparum is a major threat to global malaria control and elimination efforts. In Botswana, a southern African country approaching malaria elimination, P. falciparum molecular data are not available. Parasites were assessed through pollymerase chain reaction (PCR) for confirmation of positive rapid diagnostic tests, multiplicity of infection (MOI), and drug resistance markers among isolates from clinical uncomplicated malaria cases collected at health facilities. Of 211 dried blood spot samples selected for the study, 186 (88.2%) were PCR positive for P. falciparum. The mean MOI based on MSP1 genotyping was 2.3 and was not associated with age. A high prevalence of wild-type parasites for pfcrt and pfmdr1 was found, with a haplotype frequency (K76/N86) of 88.8% and 17.7% of the isolates having two copies of the pfmdr1 gene. For pfATPase6, all the parasites carried the wild-type S769 allele. Sequencing showed no evidence of non-synonymous mutations associated with reduced artemisinin derivative sensitivity in the P. falciparum k13 gene. In conclusion, we found that P. falciparum parasites in Botswana were mostly wild type for the drug resistance markers evaluated. Yet, there was a high rate of a molecular marker associated to reduced sensitivity to lumefantrine. Our results indicate the need for systematic drug efficacy surveillance to complement malaria elimination efforts.

Genetic polymorphism of Merozoite Surface Protein 1 (msp1) and 2 (msp2) genes and multiplicity of Plasmodium falciparum infection across various endemic areas in Senegal

INTRODUCTION

Despite a significant decline in Senegal, malaria remains a burden in various parts of the country. Assessment of multiplicity of Plasmodium falciparum infection and genetic diversity of parasites population could help in monitoring of malaria control.

OBJECTIVE

To assess genetic diversity and multiplicity of infection in P. falciparum isolates from three areas in Senegal with different malaria transmissions.

METHODS

136 blood samples were collected from patients with uncomplicated P. falciparum malaria in Pikine, Kedougou and Thies. Polymorphic loci of msp1 and 2 (Merozoite surface protein-1 and 2) genes were amplified by nested PCR.

RESULTS

For msp1gene, K1 allelic family was predominant with frequency of 71%. Concerning msp2 gene, IC3D7 allelic family was the most represented with frequency of 83%. Multiclonal isolates found were 36% and 31% for msp1et msp2 genes respectively. The MOI found in all areas was 2.56 and was statistically different between areas (P=0.024). Low to intermediate genetic diversity were found with heterozygosity range (He=0,394-0,637) and low genetic differentiation (Fst msp1= 0.011; Fst msp2=0.017) were observed between P. falciparum population within the country.

CONCLUSION

Low to moderate genetic diversity of P.falciparum strains and MOI disparities were found in Senegal.

Association of high Plasmodium falciparum parasite densities with polyclonal microscopic infections in asymptomatic children from Toubacouta, Senegal

BACKGROUND

Malaria is a leading cause of mortality and morbidity in tropical countries, especially in sub-Saharan Africa. In Senegal, a control plan implemented in the beginning of the 2000s has enabled a substantial reduction of mortality and morbidity due to malaria. However, eradication of malaria requires a vaccine that protects against Plasmodium falciparum the deadliest species of the parasite that causes this disease. Plasmodium falciparum is characterized by an extensive genetic diversity that makes vaccine development challenging. In this study, the diversity of P. falciparum isolates was analysed from asymptomatic children residing in the district of Toubacouta, Senegal.

METHODS

A nested PCR approach was used to perform genotyping of the msp-1 and msp-2 loci in samples from 87 asymptomatic children infected with P. falciparum, collected during a cross sectional survey in November and December 2010. Parasite densities in blood samples were determined by microscopic examination and statistical analyses were used to identify association of parasite genotype and parasitaemia.

RESULTS

Genotyping was successful in 84/87 and 82/87 samples for msp-1 and msp-2, respectively. A strong genetic diversity was found with a total of 15 and 21 different alleles identified for msp-1 and msp-2, respectively. RO33 was the most frequent allelic family of msp-1 followed by MAD20, then by K1. Regarding msp-2 allelic families, 3D7 was more common than FC27. Multiple infections were predominant, since 69% and 89% of the samples genotyped for msp-1 and msp-2 showed more than one clone of P. falciparum with complexity of infection (COI) of 2.5 and 4.7, respectively. Expected heterozygosity (H_E) was 0.57 and 0.55 for msp-1 and msp-2, respectively. Interestingly, polyclonal infections were significantly associated with higher parasitaemia.

CONCLUSIONS

The strong genetic diversity of P. falciparum clones and the association of polyclonal infection with high parasitaemia call for a multi-allelic approach in the design of vaccine candidates for efficient malaria eradication.

Association Between Age and Plasmodium falciparum Infection Dynamics

Few data exist on the incidence or duration of natural Plasmodium falciparum infections in high-transmission settings. School-aged children (SAC) carry a disproportionate burden of infections, suggesting either increased incidence or increased duration. We estimated the incidence and duration of unique infections according to age groups. The Mfera Cohort Study (2014-2017) in Malawi had 2 years of follow-up, with 120 participants tested monthly and during sick visits. Blood samples were collected to detect P. falciparum by microscopy and polymerase chain reaction. Positive samples underwent genotyping. Simulation was used to account for high rates of nondetection of infection among low-parasitemia infections, which increase in frequency with age. Adults had significantly fewer unique infections per person per year (median, 2.5) compared with SAC and children younger than 5 years of age (6.3 and 6.6, respectively). Over half of all genotypes were persistent. Infections lasted significantly longer in adults (median, 180 days) and SAC (median, 163 days) compared with children younger than 5 years of age (median, 97 days), after accounting for age-dependent nondetection of infection. SAC acquired new infections at the same rate as children younger than 5 years, but they maintained these infections for longer periods of time, similar to adults. This study provides new insights into P. falciparum infection dynamics that should be considered when designing malaria control strategies.

Characterization of Plasmodium falciparum structure in Nigeria with malaria SNPs barcode

BACKGROUND

Plasmodium falciparum malaria remains a major health challenge in Nigeria despite the global decline of its incidence and mortality rates. Although significant progress has been made in preventing the transmission of P. falciparum and controlling the spread of the infection, there is much to be done in the area of proper monitoring, surveillance of the parasite, investigating the population dynamics and drug resistance profiling of the parasite as these are important to its eventual eradication. Polymorphic loci of msp1, msp2 and/or glurp genes or microsatellites have been traditionally used to characterize P. falciparum population structure in various parts of Nigeria. The lack of standardization in the interpretation of results, as well as the inability of these methods to distinguish closely related parasites, remains a limitation of these techniques. Conversely, the recently developed 24 single nucleotide polymorphism (SNP)-based molecular barcode assay has the possibility of differentiating between closely related parasites and offer additional information in determining the population diversity of P. falciparum within and between parasite populations. This study is therefore aimed at defining the population diversity of P. falciparum in and between two localities in Nigeria using the SNPs barcode technique.

METHODS

The 24-SNP high-resolution melt (HRM) barcode assay and msp2 genotyping was used to investigate both intra and inter population diversity of the parasite population in two urban cities of Nigeria.

RESULTS

Based on SNP barcode analysis, polygenomic malaria infections were observed in 17.9% and 13.5% of population from Enugu and Ibadan, respectively, while msp2 analyses showed 21% and 19.4% polygenomic infections in Enugu and Ibadan, respectively. Low levels of genetic diversity (π) of 0.328 and 0.318 were observed in Enugu and Ibadan parasite populations, respectively, while the F_ST value of 0.02 (p = 0.055) was obtained when the genetic divergence of both populations was considered.

CONCLUSIONS

The 24-SNP barcode assay was effective in analysing P. falciparum population diversity. This study also showed that P. falciparum populations in Enugu and Ibadan had a degree of intra-population diversity, but very low divergence between the population. A low degree of polygenomic infections were also observed in the two parasite populations unlike previous years. This maybe as a result of the effect of artemisinin-based combination therapy (ACT), long-lasting insecticide-treated nets (LLITNs) and intermittent preventive treatments in the study populations.

To test or not: occurrence of sickle cell trait and assessment of the awareness toward its screening among patients attending Magale Health Center IV, Namisindwa District, Eastern Uganda

PURPOSE

To evaluate the occurrence of sickle cell trait (SCT), assess patient awareness and evaluate the performance of a sickle cell hemoglobin-S (dithionate-qualitative solubility) point-of-care test among patients seeking care at Magale Health Center IV, Namisindwa District, Eastern Uganda.

MATERIALS AND METHODS

We conducted a cross sectional study, in which we consecutively enrolled participants aged ≥18 years at Magale Health Center IV. Four milliliters of EDTA blood were collected by venipuncture and screened for SCT using solubility testing, and confirmed with hemoglobin (Hb) electrophoresis at Central Public Health Laboratory (CPHL), Kampala, Uganda. A structured questionnaire was used to assess participants' awareness of SCT. Data were presented as proportion, and measurements of diagnostic test performance were calculated.

RESULTS

We enrolled 242 participants, of these 58.7% (N = 142) were females. Their mean age was 26.4 years (range 18-49). Of the 242 participants, 11, who represent 4.5% (95% CI: 3.3-5.9), tested positive. The sensitivity, specificity, positive predictive value and negative predictive value of the rapid sickle cell test were 63.64%, 100%, 100% and 98.30%, respectively. There was knowledge gap regarding sickle cell awareness.

CONCLUSION

The occurrence of SCT was high, and the point-of-care test showed a high diagnostic reliability. The risk of SCT is associated with genetic predisposition as indicated by Hb electrophoresis. Community sensitization is key to avert the associated risk of Hb defects.

Genetic diversity of the msp-1, msp-2, and glurp genes of Plasmodium falciparum isolates in Northwest Ethiopia

Background

Determination of the genetic diversity of malaria parasites can inform the intensity of transmission and identify potential deficiencies in malaria control programmes. This study was conducted to characterize the genetic diversity and allele frequencies of Plasmodium falciparum in Northwest Ethiopia along the Eritrea and Sudan border.

Methods

A total of 90 isolates from patients presenting to the local health centre with uncomplicated P. falciparum were collected from October 2014 to January 2015. DNA was extracted and the polymorphic regions of the msp-1, msp-2 and glurp loci were genotyped by nested polymerase chain reactions followed by gel electrophoresis for fragment analysis.

Results

Allelic variation in msp-1, msp-2 and glurp were identified in 90 blood samples. A total of 34 msp alleles (12 for msp-1 and 22 for msp-2) were detected. For msp-1 97.8% (88/90), msp-2 82.2% (74/90) and glurp 46.7% (42/90) were detected. In msp-1, MAD20 was the predominant allelic family detected in 47.7% (42/88) of the isolates followed by RO33 and K1. For msp-2, the frequency of FC27 and IC/3D7 were 77% (57/74) and 76% (56/74), respectively. Nine glurp RII region genotypes were identified. Seventy percent of isolates had multiple genotypes and the overall mean multiplicity of infection was 2.6 (95% CI 2.25–2.97). The heterozygosity index was 0.82, 0.62 and 0.20 for msp-1, msp-2 and glurp, respectively. There was no significant association between multiplicity of infection and age or parasite density.

Conclusions

There was a high degree of genetic diversity with multiple clones in P. falciparum isolates from Northwest Ethiopia suggesting that there is a need for improved malaria control efforts in this region.

Electronic supplementary material

The online version of this article (10.1186/s12936-018-2540-x) contains supplementary material, which is available to authorized users.

Role of genetic factors and ethnicity on the multiplicity of Plasmodium falciparum infection in children with asymptomatic malaria in Yaoundé, Cameroon

In this cross-sectional study, we investigated host genetic factors and ethnic variation in circulating Plasmodium falciparum merozoite surface protein 2 (msp-2) clones among children with asymptomatic malaria. Isolates from seventy two asymptomatic malaria children were used for genotyping block 3 of msp-2 gene by nested polymerase chain reaction (PCR). Sickle cell trait and glucose-6-phosphate dehydrogenase (G6PD) deficiency were analysed by restriction fragment length polymorphism of DNA products from PCR targeting codons 6 and 68 of the beta-globin (HBB) and G6PD genes respectively. ABO blood group was typed by agglutination method. A total of forty two msp-2 genotypes (20 for 3D7 and 22 for FC27) were detected for an average (standard error of mean) multiplicity of infection (MOI) of 2.45 (0.16). The MOI was statistically the same among the five identified ethnic groups (P = 0.83). The overall prevalence of sickle cell trait and G6PD deficiency were 12.50 % and 22.22 % respectively. MOI was similar between children with Hb AA and Hb AS genotypes (P = 0.42). MOI was significantly high among children with a mutant G6PD genotype (P = 0.017). MOI was significantly higher in blood group O than group A (P = 0.03). Our findings show that although ethnicity and sickle cell trait have no association with MOI, the association was observed with G6PD genotype and ABO group. The results suggest the need for extension and expansion of the current study in order to investigate the mechanisms involved.

Multiscale Immune Selection and the Transmission-Diversity Feedback in Antigenically Diverse Pathogen Systems

Antigenic diversity is commonly used by pathogens to enhance their transmission success. Within-host clonal antigenic variation helps to maintain long infectious periods, whereas high levels of allelic diversity at the population level significantly expand the pool of susceptible individuals. Diversity, however, is not necessarily a static property of a pathogen population but in many cases is generated by the very act of infection and transmission, and it is therefore expected to respond dynamically to changes in transmission and immune selection. We hypothesized that this coupling creates a positive feedback whereby infection and disease transmission promote the generation of diversity, which itself facilitates immune evasion and further infections. To investigate this link in more detail, we considered the human malaria parasite Plasmodium falciparum, one of the most important antigenically diverse pathogens. We developed an individual-based model in which antigenic diversity emerges as a dynamic property from the underlying transmission processes. Our results show that the balance between stochastic extinction and the generation of new antigenic variants is intrinsically linked to within-host and between-host immune selection. This in turn determines the level of diversity that can be maintained in a given population. Furthermore, the transmission-diversity feedback can lead to temporal lags in the response to natural or intervention-induced perturbations in transmission rates. Our results therefore have important implications for monitoring and assessing the effectiveness of disease control efforts.

Plasmodium falciparum msp1 and msp2 genetic diversity and allele frequencies in parasites isolated from symptomatic malaria patients in Bobo-Dioulasso, Burkina Faso

Background

In Burkina Faso, malaria remains the overall leading cause of morbidity and mortality accounting for 35.12% of consultations, 40.83% of hospitalizations and 37.5% of deaths. Genotyping of malaria parasite populations remains an important tool to determine the types and number of parasite clones in an infection. The present study aimed to evaluate the merozoite surface protein 1 (msp1) and merozoite surface protein 2 (msp2) genetic diversity and allele frequencies in Bobo-Dioulasso, Burkina Faso.

Method

Dried blood spots (DBS) were collected at baseline from patients with uncomplicated malaria in urban health centers in Bobo-Dioulasso. Parasite DNA was extracted using chelex-100 and species were identified using nested PCR. Plamodium falciparum msp1 and msp2 genes were amplified by nested polymerase chain reaction (PCR) and PCR products were analyzed by electrophoresis on a 2.5% agarose gel. Alleles were categorized according to their molecular weight.

Results

A total of 228 blood samples were analyzed out of which 227 (99.9%) were confirmed as P. falciparum-positive and one sample classified as mixed infection for P. malaria and P. falciparum. In msp1, the K1 allelic family was predominant with 77.4% (162/209) followed respectively by the MAD20 allelic family with 41.3% and R033 allelic family with 36%. In msp2, the 3D7 allelic family was the most frequently detected with 93.1 % compared to FC27 with 41.3%. Twenty-one different alleles were observed in msp1 with 9 alleles for K1, 8 alleles for MAD20 and 4 alleles for R033. In msp2, 25 individual alleles were detected with 10 alleles for FC27 and 15 alleles for 3D7. The mean multiplicity of falciparum infection was 1.95 with respectively 1.8 (1.76–1.83) and 2.1 (2.03–2.16) for msp1 and msp2 (P = 0.01).

Conclusions

Our study showed high genetic diversity and allelic frequencies of msp1 and msp2 in Plasmodium falciparum isolates from symptomatic malaria patients in Bobo-Dioulasso.

A deep sequencing approach to estimate Plasmodium falciparum complexity of infection (COI) and explore apical membrane antigen 1 diversity

BACKGROUND

Humans living in regions with high falciparum malaria transmission intensity harbour multi-strain infections comprised of several genetically distinct malaria haplotypes. The number of distinct malaria parasite haplotypes identified from an infected human host at a given time is referred to as the complexity of infection (COI). In this study, an amplicon-based deep sequencing method targeting the Plasmodium falciparum apical membrane antigen 1 (pfama1) was utilized to (1) investigate the relationship between P. falciparum prevalence and COI, (2) to explore the population genetic structure of P. falciparum parasites from malaria asymptomatic individuals participating in the 2007 Demographic and Health Survey (DHS) in the Democratic Republic of Congo (DRC), and (3) to explore selection pressures on geospatially divergent parasite populations by comparing AMA1 amino acid frequencies in the DRC and Mali.

RESULTS

A total of 900 P. falciparum infections across 11 DRC provinces were examined. Deep sequencing of both individuals, for COI analysis, and pools of individuals, to examine population structure, identified 77 unique pfama1 haplotypes. The majority of individual infections (64.5%) contained polyclonal (COI > 1) malaria infections based on the presence of genetically distinct pfama1 haplotypes. A minimal correlation between COI and malaria prevalence as determined by sensitive real-time PCR was identified. Population genetic analyses revealed extensive haplotype diversity, the vast majority of which was shared across the sites. AMA1 amino acid frequencies were similar between parasite populations in the DRC and Mali.

CONCLUSIONS

Amplicon-based deep sequencing is a useful tool for the detection of multi-strain infections that can aid in the understanding of antigen heterogeneity of potential malaria vaccine candidates, population genetics of malaria parasites, and factors that influence complex, polyclonal malaria infections. While AMA1 and other diverse markers under balancing selection may perform well for understanding COI, they may offer little geographic or temporal discrimination between parasite populations.

Passively versus Actively Detected Malaria: Similar Genetic Diversity but Different Complexity of Infection

The surveillance of malaria is generally undertaken on the assumption that samples passively collected at health facilities are comparable to or representative of the broader Plasmodium reservoir circulating in the community. Further characterization and comparability of the hidden asymptomatic parasite reservoir are needed to inform on the potential impact of sampling bias. This study explores the impact of sampling strategy on molecular surveillance by comparing the genetic make-up of Plasmodium falciparum and Plasmodium vivax isolates collected by passive versus active case detection. Sympatric isolates of P. falciparum and P. vivax were collected from a large community survey and ongoing clinical surveillance studies undertaken in the hypomesoendemic setting of Mimika District (Papua, Indonesia). Plasmodium falciparum isolates were genotyped at nine microsatellite loci and P. vivax at eight loci. Measures of diversity and differentiation were used to compare different patient and parasitological sample groups. The results demonstrated that passively detected cases (symptomatic) had comparable population diversity to those circulating in the community (asymptomatic) in both species. In addition, asymptomatic patent infections were as diverse as subpatent infections. However, a significant difference in multiplicity of infection (MOI) and percentage of polyclonal infections was observed between actively and passively detected P. vivax cases (mean MOI: 1.7 ± 0.7 versus 1.4 ± 1.4, respectively; P = 0.001). The study findings infer that, in hypomesoendemic settings, passive sampling is appropriate for molecular parasite surveillance strategies using the predominant clone in any given infection; however, the findings suggest caution when analyzing complexity of infection. Further evaluation is required in other endemic settings.

Comparison of the diagnostic performance of microscopic examination with nested polymerase chain reaction for optimum malaria diagnosis in Upper Myanmar

BACKGROUND

Accurate diagnosis of Plasmodium infection is crucial for prompt malaria treatment and surveillance. Microscopic examination has been widely applied as the gold standard for malaria diagnosis in most part of malaria endemic areas, but its diagnostic value has been questioned, particularly in submicroscopic malaria. In this study, the diagnostic performance of microscopic examination and nested polymerase chain reaction (PCR) was evaluated to establish optimal malaria diagnosis method in Myanmar.

METHODS

A total of 1125 blood samples collected from residents in the villages and towns located in Naung Cho, Pyin Oo Lwin, Tha Beik Kyin townships and Mandalay of Upper Myanmar were screened by microscopic examination and species-specific nested PCR method.

RESULTS

Among the 1125 blood samples, 261 samples were confirmed to be infected with malaria by microscopic examination. Evaluation of the 1125 samples by species-specific nested PCR analysis revealed that the agreement between microscopic examination and nested PCR was 87.3% (261/299). Nested PCR successfully detected 38 Plasmodium falciparum or Plasmodium vivax infections, which were missed in microscopic examination. Microscopic examinations also either misdiagnosed the infected Plasmodium species, or did not detect mixed infections with different Plasmodium species in 31 cases.

CONCLUSIONS

The nested PCR method is more reliable than conventional microscopic examination for the diagnosis of malaria infections, and this is particularly true in cases of mixed infections and submicroscopic infections. Given the observed higher sensitivity and specificity of nested PCR, the molecular method holds enormous promise in malaria diagnosis and species differentiation, and can be applied as an effective monitoring tool for malaria surveillance, control and elimination in Myanmar.

An epidemiological study to assess Plasmodium falciparum parasite prevalence and malaria control measures in Burkina Faso and Senegal

Background

Malariometric information is needed to decide how to introduce malaria vaccines and evaluate their impact in sub-Saharan African countries.

Methods

This cross-sectional study (NCT01954264) was conducted between October and November, 2013, corresponding to the high malaria transmission season, in four sites with Health and Demographic Surveillance Systems (DSS) [two sites with moderate-to-high malaria endemicity in Burkina Faso (Nouna and Saponé) and two sites with low malaria endemicity in Senegal (Keur Socé and Niakhar)]. Children (N = 2421) were randomly selected from the DSS lists of the study sites and were stratified into two age groups (6 months–4 years and 5–9 years). A blood sample was collected from each child to evaluate parasite prevalence of Plasmodium falciparum and other Plasmodium species and gametocyte density by microscopy, and rapid diagnosis test in the event of fever within 24 h. Case report forms were used to evaluate malaria control measures and other factors.

Results

Plasmodium falciparum was identified in 707 (29.2%) children, with a higher prevalence in Burkina Faso than Senegal (57.5 vs 0.9% of children). In Burkina Faso, prevalence was 57.7% in Nouna and 41.9% in Saponé in the 6 months–4 years age group, and 75.4% in Nouna and 70.1% in Saponé in the 5–9 years age group. Infections with other Plasmodium species were rare and only detected in Burkina Faso. While mosquito nets were used by 88.6–97.0 and 64.7–80.2% of children in Burkina Faso and Senegal, other malaria control measures evaluated at individual level were uncommon. In Burkina Faso, exploratory analyses suggested that use of malaria treatment or any other medication within 14 days, and use of insecticide spray within 7 days decreased the prevalence of malaria infection; older age, rural residence, natural floor, grass/palm roof, and unavailability of electricity in the house were factors associated with increased malaria occurrence.

Conclusions

Plasmodium falciparum infection prevalence in children younger than 10 years was 57.5% in Burkina Faso and 0.9% in Senegal, and variability was observed, among others, by age, study site and malaria control measures.

Spatio-temporal analysis of the genetic diversity and complexity of Plasmodium falciparum infections in Kedougou, southeastern Senegal

BACKGROUND

Genetic analyses of the malaria parasite population and its temporal and spatial dynamics could provide an assessment of the effectiveness of disease control strategies. The genetic diversity of Plasmodium falciparum has been poorly documented in Senegal, and limited data are available from the Kedougou Region. This study examines the spatial and temporal variation of the genetic diversity and complexity of P. falciparum infections in acute febrile patients in Kedougou, southeastern Senegal. A total of 263 sera from patients presenting with acute febrile illness and attending Kedougou health facilities between July 2009 and July 2013 were obtained from a collection established as part of arbovirus surveillance in Kedougou. Samples identified as P. falciparum by nested PCR were characterized for their genetic diversity and complexity using msp-1 and msp-2 polymorphic markers.

RESULTS

Samples containing only P. falciparum accounted for 60.83% (160/263) of the examined samples. All three msp-1 allelic families (K1, MAD20 and RO33) and two msp-2 allelic families (FC27 and 3D7) were detected in all villages investigated over the 5-year collection period. The average genotype per allelic family was comparable between villages. Frequencies of msp-1 and msp-2 allelic types showed no correlation with age (Fisher's exact test, P = 0.59) or gender (Fisher's exact test, P = 0.973), and were similarly distributed throughout the 5-year sampling period (Fisher's exact test, P = 0.412) and across villages (Fisher's exact test, P = 0.866). Mean multiplicity of infection (MOI) for both msp-1 and msp-2 was highest in Kedougou village (2.25 and 2.21, respectively) and among younger patients aged ≤ 15 years (2.12 and 2.00, respectively). The mean MOI was highest in 2009 and decreased progressively onward.

CONCLUSION

Characterization of the genetic diversity and complexity of P. falciparum infections in Kedougou revealed no spatio-temporal variation in the genetic diversity of P. falciparum isolates. However, mean MOI varied with time of sera collection and decreased over the course of the study (July 2009 to July 2013). This suggests a slow progressive decrease of malaria transmission intensity in Kedougou Region despite the limited impact of preventive and control measures implemented by the National Malaria Control Programme on malaria morbidity and mortality.

THE REAL McCOIL: A method for the concurrent estimation of the complexity of infection and SNP allele frequency for malaria parasites

As many malaria-endemic countries move towards elimination of Plasmodium falciparum, the most virulent human malaria parasite, effective tools for monitoring malaria epidemiology are urgent priorities. P. falciparum population genetic approaches offer promising tools for understanding transmission and spread of the disease, but a high prevalence of multi-clone or polygenomic infections can render estimation of even the most basic parameters, such as allele frequencies, challenging. A previous method, COIL, was developed to estimate complexity of infection (COI) from single nucleotide polymorphism (SNP) data, but relies on monogenomic infections to estimate allele frequencies or requires external allele frequency data which may not available. Estimates limited to monogenomic infections may not be representative, however, and when the average COI is high, they can be difficult or impossible to obtain. Therefore, we developed THE REAL McCOIL, Turning HEterozygous SNP data into Robust Estimates of ALelle frequency, via Markov chain Monte Carlo, and Complexity Of Infection using Likelihood, to incorporate polygenomic samples and simultaneously estimate allele frequency and COI. This approach was tested via simulations then applied to SNP data from cross-sectional surveys performed in three Ugandan sites with varying malaria transmission. We show that THE REAL McCOIL consistently outperforms COIL on simulated data, particularly when most infections are polygenomic. Using field data we show that, unlike with COIL, we can distinguish epidemiologically relevant differences in COI between and within these sites. Surprisingly, for example, we estimated high average COI in a peri-urban subregion with lower transmission intensity, suggesting that many of these cases were imported from surrounding regions with higher transmission intensity. THE REAL McCOIL therefore provides a robust tool for understanding the molecular epidemiology of malaria across transmission settings.

Plasmodium falciparum infection in febrile Congolese children: prevalence of clinical malaria 10 years after introduction of artemisinin-combination therapies

OBJECTIVES

To investigate the proportion of malaria infection in febrile children consulting a paediatric hospital in Brazzaville, to determine the prevalence of submicroscopic malaria infection, to characterise Plasmodium falciparum infection and compare the prevalence of uncomplicated P. falciparum malaria according to haemoglobin profiles.

METHODS

Blood samples were collected from children aged <10 years with an axillary temperature ≥37.5 °C consulting the paediatric ward of Marien Ngouabi Hospital in Brazzaville. Parasite density was determined and all samples were screened for P. falciparum by nested polymerase chain reaction (PCR) using the P. falciparum msp-2 marker to detect submicroscopic infections and characterise P. falciparum infection. Sickle cell trait was screened by PCR.

RESULTS

A total of 229 children with fever were recruited, of whom 10% were diagnosed with uncomplicated malaria and 21% with submicroscopic infection. The mean parasite density in children with uncomplicated malaria was 42 824 parasites/μl of blood. The multiplicity of infection (MOI) was 1.59 in children with uncomplicated malaria and 1.69 in children with submicroscopic infection. The mean haemoglobin level was 10.1 ± 1.7 for children with uncomplicated malaria and 12.0 ± 8.6 for children with submicroscopic infection. About 13% of the children harboured the sickle cell trait (HbAS); the rest had normal haemoglobin (HbAA). No difference in prevalence of uncomplicated malaria and submicroscopic infection, parasite density, haemoglobin level, MOI and P. falciparum genetic diversity was observed according to haemoglobin type.

CONCLUSION

The low prevalence of uncomplicated malaria in febrile Congolese children indicates the necessity to investigate carefully other causes of fever.

Genetically Determined Response to Artemisinin Treatment in Western Kenyan Plasmodium falciparum Parasites

Genetically determined artemisinin resistance in Plasmodium falciparum has been described in Southeast Asia. The relevance of recently described Kelch 13-propeller mutations for artemisinin resistance in Sub-Saharan Africa parasites is still unknown. Southeast Asia parasites have low genetic diversity compared to Sub-Saharan Africa, where parasites are highly genetically diverse. This study attempted to elucidate whether genetics provides a basis for discovering molecular markers in response to artemisinin drug treatment in P. falciparum in Kenya. The genetic diversity of parasites collected pre- and post- introduction of artemisinin combination therapy (ACT) in western Kenya was determined. A panel of 12 microsatellites and 91 single nucleotide polymorphisms (SNPs) distributed across the P. falciparum genome were genotyped. Parasite clearance rates were obtained for the post-ACT parasites. The 12 microsatellites were highly polymorphic with post-ACT parasites being significantly more diverse compared to pre-ACT (p < 0.0001). The median clearance half-life was 2.55 hours for the post-ACT parasites. Based on SNP analysis, 15 of 90 post-ACT parasites were single-clone infections. Analysis revealed 3 SNPs that might have some causal association with parasite clearance rates. Further, genetic analysis using Bayesian tree revealed parasites with similar clearance phenotypes were more closely genetically related. With further studies, SNPs described here and genetically determined response to artemisinin treatment might be useful in tracking artemisinin resistance in Kenya.

Assessment of submicroscopic infections and gametocyte carriage of Plasmodium falciparum during peak malaria transmission season in a community-based cross-sectional survey in western Kenya, 2012

Background

Although malaria control intervention has greatly decreased malaria morbidity and mortality in many African countries, further decline in parasite prevalence has stagnated in western Kenya. In order to assess if malaria transmission reservoir is associated with this stagnation, submicroscopic infection and gametocyte carriage was estimated. Risk factors and associations between malaria control interventions and gametocyte carriage were further investigated in this study.

Methods

A total of 996 dried blood spot samples were used from two strata, all smear-positives (516 samples) and randomly selected smear-negatives (480 samples), from a community cross-sectional survey conducted at peak transmission season in 2012 in Siaya County, western Kenya. Plasmodium falciparum parasite presence and density were determined by stained blood smear and by 18S mRNA transcripts using nucleic acid sequence-based amplification assay (NASBA), gametocyte presence and density were determined by blood smear and by Pfs25 mRNA-NASBA, and gametocyte diversity by Pfg377 mRNA RT-PCR and RT-qPCR.

Results

Of the randomly selected smear-negative samples, 69.6 % (334/480) were positive by 18S-NASBA while 18S-NASBA detected 99.6 % (514/516) smear positive samples. Overall, 80.2 % of the weighted population was parasite positive by 18S-NASBA vs 30.6 % by smear diagnosis and 44.0 % of the weighted population was gametocyte positive by Pfs25-NASBA vs 2.6 % by smear diagnosis. Children 5–15 years old were more likely to be parasitaemic and gametocytaemic by NASBA than individuals >15 years old or children <5 years old while gametocyte density decreased with age. Anaemia and self-reported fever within the past 24 h were associated with increased odds of gametocytaemia. Fever was also positively associated with parasite density, but not with gametocyte density. Anti-malarial use within the past 2 weeks decreased the odds of gametocytaemia, but not the odds of parasitaemia. In contrast, recent anti-malarial use was associated with lowered parasite density, but not the gametocyte density. Use of ITNs was associated with lower odds for parasitaemia in part of the study area with a longer history of ITN interventions. In the same part of study area, the odds of having multiple gametocyte alleles were also lower in individuals using ITNs than in those not using ITNs and parasite density was positively associated with gametocyte diversity.

Conclusion

A large proportion of submicroscopic parasites and gametocytes in western Kenya might contribute to the stagnation in malaria prevalence, suggesting that additional interventions targeting the infectious reservoir are needed. As school aged children and persons with anaemia and fever were major sources for gametocyte reservoir, these groups should be targeted for intervention and prevention to reduce malaria transmission. Anti-malarial use was associated with lower parasite density and odds of gametocytaemia, but not the gametocyte density, indicating a limitation of anti-malarial impact on the transmission reservoir. ITN use had a protective role against parasitaemia and gametocyte diversity in western Kenya.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1482-4) contains supplementary material, which is available to authorized users.

Multiplicity of infection and genetic diversity of Plasmodium falciparum isolates from patients with uncomplicated and severe malaria in Gezira State, Sudan

BACKGROUND

Multiplicity and genetic diversity of Plasmodium falciparum infection might play a role in determining the clinical outcome of malaria infection and could be a fair reflection of the disease transmission rate. This study investigated the genetic diversity of P. falciparum and multiplicity of infection in relation to the severity of malaria and age of patients in Gezira State, Sudan.

METHODS

A cross-sectional health facilities-based survey was conducted in Gezira State, Sudan in January 2012. A total of 140 P. falciparum malaria patients diagnosed with microscopy and confirmed using nested PCR were recruited and classified into uncomplicated malaria and severe malaria states according to the standard WHO criteria. DNA was extracted and MSP1 and MSP2 allelic families were determined using nested PCR.

RESULTS

The overall multiplicity of infection (MOI) was 2.25 and 2.30 and 2.15 for uncomplicated and severe malaria respectively. There were no statistically significant differences between uncomplicated and severe malaria (SM) patient groups in MOI with regard to MSP1, MSP2 and overall MOI (Mann-Whitney U-test; all P < 0.05). The predominant MSP1 allelic families were MAD20 for uncomplicated malaria and RO33 for severe malaria. The distribution of both FC27 and IC1/3D7 MSP2 allelic families were approximately the same across disease severity. One hundred and eleven P. falciparum isolates (81 %) consisted of multiple genotypes; 71/90 (78.9 %) in uncomplicated malaria and 40/50 (85.1 %) in severe malaria patient groups. Neither MSP1 nor MSP2 allelic families showed association with malaria severity. No statistically significant differences in multiplicity of infection were observed between different age groups.

CONCLUSION

In this study the majority of P. falciparum isolates from uncomplicated and severe malaria patients consisted of multiple genotypes. Further molecular epidemiological studies delineate the link between P. falciparum genotype with the malaria phenotype in different regions are encouraged.

Plasmodium falciparum Genetic Diversity in Bangladesh Does Not Suggest a Hypoendemic Population Structure

Despite the recommendation for the use of merozoite surface protein 1 (msp1), merozoite surface protein 2 (msp2), and glutamate-rich protein (glurp) genes as markers in drug efficacy studies by World Health Organization and their limited use in Bangladesh, the circulating Plasmodium falciparum population genetic structure has not yet been assessed in Bangladesh. This study presents a comprehensive report on the circulating P. falciparum population structure based on msp1, msp2, and glurp polymorphic gene markers in Bangladesh. Among the 130 pretreatment (day 0) P. falciparum samples from seven malaria-endemic districts, 14 distinct genotypes were observed for msp1, 20 for msp2, and 13 for glurp Polyclonal infection was reported in 94.6% (N = 123) of the samples. Multiplicity of infection (MOI) for msp1 was the highest (1.5) among the MOIs of the markers. The heterozygosity for msp1, msp2, and glurp was 0.89, 0.93, and 0.83, respectively. Data according to different malaria-endemic areas are also presented and discussed. Bangladesh is considered as a malaria-hypoendemic country. However, the prevalence of polyclonal infection and the genetic diversity of P. falciparum do not represent hypoendemicity.

High heterogeneity of malaria transmission and a large sub-patent and diverse reservoir of infection in Wusab As Safil district, Republic of Yemen

Background

Yemen remains the country with the highest malaria transmission within the Arabian Peninsula and a source of imported cases to neighbouring countries.

Methods

This study collected samples from individuals resident in a valley in Western Yemen as a baseline to examine infection prevalence for a future trial. As well as rapid diagnostic test (RDT) and microscopy, a filter paper blood spot was collected for molecular and serological analyses.

Results

Samples were collected from 2261 individuals from 12 clusters across a study area of approximately 100 km². Plasmodium falciparum infection prevalence was 12.4, 11.1 and 19.6 % by RDT, microscopy and polymerase chain reaction (PCR), respectively. RDT and microscopy did not detect 45 % of infections present, suggesting many infections were low-density. Infection prevalence and seroprevalence were highly heterogeneous between clusters, with evidence of higher exposure in clusters close to the wadi. The mean multiplicity of infection (MOI) was 2.3 and high heterozygosity and allelic richness were detected.

Conclusions

This highly diverse parasite population suggests a high degree of transmissibility and coupled with the substantial proportion of low-density infections, may pose challenges for malaria control and elimination efforts.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1249-y) contains supplementary material, which is available to authorized users.

Detection of chloroquine and artemisinin resistance molecular markers in Plasmodium falciparum: A hospital based study

Introduction:

Emergence of chloroquine (CQ) resistance in Plasmodium falciparum has increased the morbidity and mortality of falciparum malaria worldwide. Artemisinin-based combination therapies are now recommended by the World Health Organization as the first line treatment for falciparum malaria. Numerous molecular markers have been implicated in the CQ and artemisinin resistance.

Materials and Methods:

A total of 26 confirmed cases of falciparum malaria (by giemsa stained thick and thin smear, quantitative buffy coat, immunochromatographic test, or polymerase chain reaction [PCR]) were included in the study. About 5 ml of ethylenediaminetetraacetic acid blood sample was collected and stored at −20°C till use. Plasmodium DNA was extracted using QIAamp whole blood DNA extraction kit. PCR was done to amplify pfcrt, pfmdr1, pfserca, and pfmrp1 genes and the amplicons obtained were sequenced by Macrogen, Inc., Korea. Single nucleotide polymorphism (SNP) analysis was done using Bio-Edit Sequence Alignment Editor.

Results:

Out of the four genes targeted, we noted a SNP in the pfcrt gene alone. This SNP (G > T) was noted in the 658^th position of the gene, which was seen in 13 patients. The pfmdr1 and pfserca genes were present in 9 and 14 patients respectively. But we could not find any SNPs in these genes. This SNP in pfcrt gene was not significantly associated with any adverse outcome and neither altered disease progression.

Conclusion:

Presence of a single SNP may not be associated with any adverse clinical outcome. As the sample size was small, we may have not been able to detect any other known or unknown polymorphisms.

Genetic diversity of Plasmodium falciparum isolates from concurrent malaria and arbovirus co-infections in Kedougou, southeastern Senegal

Background

Concurrent malaria and arbovirus infections are common and represent an important public health concern in regions where both diseases are endemic. The present study investigates the genetic diversity and complexity of Plasmodium falciparum infection in concurrent malaria-arbovirus infections in Kedougou region, southeastern Senegal.

Methods

Parasite DNA was extracted from 60 to 27 sera samples collected from P. falciparum isolates of malaria and concurrent malaria-arbovirus infected patients, respectively, and followed by PCR-genotyping targeting the msp-1 (block2) and msp-2 (block3) allelic families.

Results

The mean number of genotype per allelic family was comparable between the two groups. K1 was the predominant msp-1 allelic type both in malaria (94.91 %) and arbovirus-malaria (92.59 %) groups, whereas IC/3D7 was the most prevalent msp-2 allelic type in malaria (94.91 %) and arbovirus-malaria (96.29 %) groups. Frequencies of msp-1 and msp-2 allelic types were statistically comparable between the two groups (Fisher exact test, P > 0.05) and were not associated with age. FC27 was strikingly the least prevalent in both groups and was absent in children under 5 years of age. The proportions of P. falciparum isolates from malaria-infected patients carrying the three msp-1 allelic types (67.44 %) or the two msp-2 allelic types (76.47 %) were significantly higher than those from arbovirus-malaria co-infected patients (Exact binomial test, P < 0.05). The multiplicities of infection (MOI) were low and comparable for msp-1 (1.19 vs 1.22) and msp-2 (1.11 vs 1.10), respectively between malaria and arbovirus-malaria groups.

Conclusion

The study showed no difference in the genetic diversity between P. falciparum isolates from malaria and concurrent malaria-arbovirus infected patients in Kedougou. The MOI was low despite intense malaria transmission in Kedougou. The overall results suggest a limited or no influence of arbovirus infections on P. falciparum diversity and complexity of malaria infection.

Genetic diversity among Plasmodium vivax isolates along the Thai-Myanmar border of Thailand

Background

Knowledge of the population genetics and transmission dynamics of Plasmodium vivax is crucial in predicting the emergence of drug resistance, relapse pattern and novel parasite phenotypes, all of which are relevant to the control of vivax infections. The aim of this study was to analyse changes in the genetic diversity of P. vivax genes from field isolates collected at different times along the Thai–Myanmar border.

Methods

Two hundred and fifty-four P. vivax isolates collected during two periods 10 years apart along the Thai–Myanmar border were analysed. The parasites were genotyped by nested-PCR and PCR–RFLP targeting selected polymorphic loci of Pvmsp1, Pvmsp3α and Pvcsp genes.

Results

The total number of distinguishable allelic variants observed for Pvcsp, Pvmsp1, and Pvmsp3α was 17, 7 and 3, respectively. High genetic diversity was observed for Pvcsp (H_E = 0.846) and Pvmsp1 (H_E = 0.709). Of the 254 isolates, 4.3 and 14.6 % harboured mixed Pvmsp1 and Pvcsp genotypes with a mean multiplicity of infection (MOI) of 1.06 and 1.15, respectively. The overall frequency of multiple genotypes was 16.9 %. When the frequencies of allelic variants of each gene during the two distinct periods were analysed, significant differences were noted for Pvmsp1 (P = 0.018) and the Pvcsp (P = 0.033) allelic variants.

Conclusion

Despite the low malaria transmission levels in Thailand, P. vivax population exhibit a relatively high degree of genetic diversity along the Thai–Myanmar border of Thailand, in particular for Pvmsp1 and Pvcsp, with indication of geographic and temporal variation in frequencies for some variants. These results are of relevance to monitoring the emergence of drug resistance and to the elaboration of measures to control vivax malaria.