Genetic diversity of Plasmodium falciparum isolates from uncomplicated malaria cases in Ghana over a decade

Plasmodium falciparum genetic diversity and multiplicity of infection in northern and southern Ghana assessed by amplicon sequencing

Malaria is a significant public health challenge in Ghana, with Plasmodium falciparum accounting for 80-90 % of infections. This study aimed to determine whether different climatic conditions, demographics, transmission patterns, and control practices in northern and southern Ghana result in differences in the genetic diversity, population structure, and evolutionary dynamics of P. falciparum. A total of 354 clinical samples collected in 2018 and 2021 were analyzed using the amplicon sequencing approach, targeting the CSP, AMA1, SERA2, and TRAP genes. Parasite populations from both northern and southern Ghana exhibited high haplotype diversity (Hd = 0.93-0.98). More than 70 % of the patient samples contained multiclonal infections, and the multiplicity of infection was significantly higher in northern (2.91) than in southern Ghana (2.42). Despite such a difference, extensive haplotype sharing was observed. The haplotype network and phylogenetic analyses highlighted substantial genetic connectivity among the parasite populations, likely driven by multiple factors, including human movement and shared vectors. Predominant haplotypes were consistent across regions and years, reflecting a stable pool of core haplotypes, which was not significantly impacted by contemporary control measures. In conclusion, this study underscored the high genetic diversity and connectivity of P. falciparum populations in Ghana despite different transmission ecology and the implementation of divergent control measures.

Plasmodium falciparum merozoite surface protein 2 genetic polymorphism and multiplicity of infection in selected malarious areas of Northwest Ethiopia

BACKGROUND

The genetic diversity of Plasmodium falciparum provides the parasite with many effective immune evasion and drug resistance mechanisms. This phenomenon is a major problem in eradicating malaria globally. This study aimed to assess merozoite surface protein 2 polymorphisms in P. falciparum isolates from Northwest Ethiopia.

METHOD

A cross-sectional study was conducted to assess merozoite surface protein 2 polymorphisms in P. falciparum isolates from selected malarious areas in Northwest Ethiopia from April to June 2021. A convenience sampling technique was used to select 150 study participants. A finger prick blood sample was collected to prepare blood films and dried blood spots for molecular genotyping. The merozoite surface protein 2 allele frequency and multiplicity of infection were computed. Linear regression was employed to evaluate the associations between the multiplicity of infection, parasite density, and age by calculating Spearman's rank correlation coefficients. A P value < 0.05 was considered to indicate statistical significance.

RESULT

Polymorphism analysis was performed on 126 P. falciparum isolates. There were 38 different merozoite surface protein 2 alleles, 20 of which corresponded to the IC/3D7 allelic family and 18 to the FC27 allelic family. Most patients contained multiple infections, and the mean multiplicity of infection was 3.46. There was no statistically significant difference in the multiplicity of infection in relation to the age of patients (P = 0.646). However, a statistically significant correlation was found between parasite density and the multiplicity of infection (P = 0.046). The heterozygosity index for merozoite surface protein 2 was 0.948.

CONCLUSION

This study showed that P. falciparum isolates contain multiple genotypes with a high multiplicity of infections and mixed strain infection, suggesting extensive genetic diversity and a high level of malaria transmission. This genetic variability could complicate malaria treatment and control efforts, as it can facilitate the emergence and spread of drug-resistant strains. Consequently, the findings highlight the complex malaria epidemiology in the region and emphasize the need for intensified efforts to control malaria transmission and prevent the probable emergence of drug resistance alleles in the study area.

Plasmodium falciparum population structure inferred by msp1 amplicon sequencing of parasites collected from febrile patients in Kenya

BACKGROUND

Multiplicity of infection (MOI) is an important measure of Plasmodium falciparum diversity, usually derived from the highly polymorphic genes, such as msp1, msp2 and glurp as well as microsatellites. Conventional methods of deriving MOI lack fine resolution needed to discriminate minor clones. This study used amplicon sequencing (AmpliSeq) of P. falciparum msp1 (Pfmsp1) to measure spatial and temporal genetic diversity of P. falciparum.

METHODS

264 P. falciparum positive blood samples collected from areas of differing malaria endemicities between 2010 and 2019 were used. Pfmsp1 gene was amplified and amplicon libraries sequenced on Illumina MiSeq. Sequences were aligned against a reference sequence (NC_004330.2) and clustered to detect fragment length polymorphism and amino acid variations.

RESULTS

Children < 5 years had higher parasitaemia (median = 23.5 ± 5 SD, p = 0.03) than the > 5-14 (= 25.3 ± 5 SD), and those > 15 (= 25.1 ± 6 SD). Of the alleles detected, 553 (54.5%) were K1, 250 (24.7%) MAD20 and 211 (20.8%) RO33 that grouped into 19 K1 allelic families (108-270 bp), 14 MAD20 (108-216 bp) and one RO33 (153 bp). AmpliSeq revealed nucleotide polymorphisms in alleles that had similar sizes, thus increasing the K1 to 104, 58 for MAD20 and 14 for RO33. By AmpliSeq, the mean MOI was 4.8 (± 0.78, 95% CI) for the malaria endemic Lake Victoria region, 4.4 (± 1.03, 95% CI) for the epidemic prone Kisii Highland and 3.4 (± 0.62, 95% CI) for the seasonal malaria Semi-Arid region. MOI decreased with age: 4.5 (± 0.76, 95% CI) for children < 5 years, compared to 3.9 (± 0.70, 95% CI) for ages 5 to 14 and 2.7 (± 0.90, 95% CI) for those > 15. Females' MOI (4.2 ± 0.66, 95% CI) was not different from males 4.0 (± 0.61, 95% CI). In all regions, the number of alleles were high in the 2014-2015 period, more so in the Lake Victoria and the seasonal transmission arid regions.

CONCLUSION

These findings highlight the added advantages of AmpliSeq in haplotype discrimination and the associated improvement in unravelling complexity of P. falciparum population structure.

coiaf: Directly estimating complexity of infection with allele frequencies

In malaria, individuals are often infected with different parasite strains. The complexity of infection (COI) is defined as the number of genetically distinct parasite strains in an individual. Changes in the mean COI in a population have been shown to be informative of changes in transmission intensity with a number of probabilistic likelihood and Bayesian models now developed to estimate the COI. However, rapid, direct measures based on heterozygosity or FwS do not properly represent the COI. In this work, we present two new methods that use easily calculated measures to directly estimate the COI from allele frequency data. Using a simulation framework, we show that our methods are computationally efficient and comparably accurate to current approaches in the literature. Through a sensitivity analysis, we characterize how the distribution of parasite densities, the assumed sequencing depth, and the number of sampled loci impact the bias and accuracy of our two methods. Using our developed methods, we further estimate the COI globally from Plasmodium falciparum sequencing data and compare the results against the literature. We show significant differences in the estimated COI globally between continents and a weak relationship between malaria prevalence and COI.

Therapeutic efficacy of dihydroartemisinin-piperaquine combination for the treatment of uncomplicated malaria in Ghana

In 2020, Dihydroartemisinin-Piperaquine (DHAP) was adopted as a second-line antimalarial for treatment of uncomplicated malaria in Ghana following a review of the country's antimalarial medicines policy. Available data obtained in 2007 had shown PCR-uncorrected therapeutic efficacy of 93.3% using a 28-day follow-up schedule. In 2020, the standard 42-day follow-up schedule for DHAP was used to estimate efficacy levels among febrile children aged 6 months to 9 years in three malaria sentinel sites representing the three main ecological zones of the country- savannah, forest, and coastal. PCR genotyping distinguished between recrudescence and re-infection using merozoite surface protein 2 (MSP2)-specific primers for FC27 and 3D7 strains. Per protocol analyses showed day 28 efficacy of 100% in all three sentinel sites with day 42 PCR-corrected efficacy ranging between 90.3% (95% CI: 80.1 - 96.4%) in the savannah zone and 100% in the forest and coastal zones, yielding a national average of 97.0% (95% CI: 93.4 - 98.8). No day 3 parasitemia was observed in all three sites. Prevalence of measured fever (axillary temperature ≥ 37.5°C) declined from 50.0 - 98.8% on day 0 to 7.1-11.5% on day 1 whilst parasitemia declined from 100% on day 0 to 1.2 - 2.3% on day 1. Mean haemoglobin levels on days 28 and 42 were significantly higher than pre-treatment levels in all three sites. We conclude that DHAP is highly efficacious in the treatment of uncomplicated malaria in Ghana. This data will serve as baseline for subsequent DHAP efficacy studies in the country.

Plasmodium vivax: the potential obstacles it presents to malaria elimination and eradication

Initiatives to eradicate malaria have a good impact on P. falciparum malaria worldwide. P. vivax, however, still presents significant difficulties. This is due to its unique biological traits, which, in comparison to P. falciparum, pose serious challenges for malaria elimination approaches. P. vivax's numerous distinctive characteristics and its ability to live for weeks to years in liver cells in its hypnozoite form, which may elude the human immune system and blood-stage therapy and offer protection during mosquito-free seasons. Many malaria patients are not fully treated because of contraindications to primaquine use in pregnant and nursing women and are still vulnerable to P. vivax relapses, although there are medications that could radical cure P. vivax. Additionally, due to CYP2D6's highly variable genetic polymorphism, the pharmacokinetics of primaquine may be impacted. Due to their inability to metabolize PQ, some CYP2D6 polymorphism alleles can cause patients to not respond to treatment. Tafenoquine offers a radical treatment in a single dose that overcomes the potentially serious problem of poor adherence to daily primaquine. Despite this benefit, hemolysis of the early erythrocytes continues in individuals with G6PD deficiency until all susceptible cells have been eliminated. Field techniques such as microscopy or rapid diagnostic tests (RDTs) miss the large number of submicroscopic and/or asymptomatic infections brought on by reticulocyte tropism and the low parasitemia levels that accompany it. Moreover, P. vivax gametocytes grow more quickly and are much more prevalent in the bloodstream. P. vivax populations also have a great deal of genetic variation throughout their genome, which ensures evolutionary fitness and boosts adaptation potential. Furthermore, P. vivax fully develops in the mosquito faster than P. falciparum. These characteristics contribute to parasite reservoirs in the human population and facilitate faster transmission. Overall, no genuine chance of eradication is predicted in the next few years unless new tools for lowering malaria transmission are developed (i.e., malaria elimination and eradication). The challenging characteristics of P. vivax that impede the elimination and eradication of malaria are thus discussed in this article.

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.

Short-term cryopreservation and thawing have minimal effects on Plasmodium falciparum ex vivo invasion profile

Ex vivo phenotyping of P. falciparum erythrocyte invasion diversity is important in the identification and down selection of potential malaria vaccine targets. However, due to the lack of appropriate laboratory facilities in remote areas of endemic countries, direct processing of P. falciparum clinical isolates is usually not feasible. Here, we investigated the combined effect of short-term cryopreservation and thawing processes on the ex vivo invasion phenotypes of P. falciparum isolates. Ex-vivo or in vitro invasion phenotyping assays were performed with P. falciparum clinical isolates prior to or following culture adaptation, respectively. All isolates were genotyped at Day 0 for parasite clonality. Subsequently, isolates that were successfully culture-adapted were genotyped again at Days 7, 15, 21, and 28-post adaptation. Invasion phenotyping assays were performed in isogenic isolates revived at different time points (3, 6, and 12 months) post-cryopreservation and the resulting data were compared to that from ex-vivo invasion data of matched isogenic parental isolates. We also show that short-term culture adaptation selects for parasite clonality and could be a driving force for variation in invasion phenotypes as compared to ex vivo data where almost all parasite clones of a given isolate are present. Interestingly, our data show little variation in the parasites' invasion phenotype following short-term cryopreservation. Altogether, our data suggest that short-term cryopreservation of uncultured P. falciparum clinical isolates is a reliable mechanism for storing parasites for future use.

DNA recovery from used malaria RDT to detect Plasmodium species and to assess Plasmodium falciparum genetic diversity: a pilot study in Madagascar

Background

Rapid diagnostic tests (RDT) are widely used for malaria diagnosis in Madagascar, where Plasmodium falciparum is the predominant species. Molecular diagnosis is essential for malaria surveillance, but requires additional blood samples for DNA extraction. Used RDTs is an attractive alternative that can be used as a source of DNA. Plasmodium falciparum genetic diversity and multiplicity of infection, usually determined by the genotyping of polymorphic regions of merozoite surface proteins 1 and 2 genes (msp1, msp2), and the repeated region RII of the glutamate-rich protein gene (glurp) have been associated with malaria transmission levels and subsequently with the impact of the deployed control strategies.

Thus, the study aims to use RDT as DNA source to detect Plasmodium species, to characterize Plasmodium falciparum genetic diversity and determine the multiplicity of infection.

Methods

A pilot study was conducted in two sites with different epidemiological patterns: Ankazomborona (low transmission area) and Matanga (high transmission area). On May 2018, used RDT (SD BIOLINE Malaria Ag P.f/Pan, 05FK63) were collected as DNA source. Plasmodium DNA was extracted by simple elution with nuclease free water. Nested-PCR were performed to confirm Plasmodium species and to analyse P. falciparum msp1, msp2 and glurp genes polymorphisms.

Results

Amongst the 170 obtained samples (N = 74 from Ankazomborona and N = 96 from Matanga), Plasmodium positivity rate was 23.5% (40/170) [95% CI 17.5–30.8%] by nested-PCR with 92.2% (37/40) positive to P. falciparum, 5% (2/40) to Plasmodium vivax and 2.5% (1/40) to P. falciparum/P. vivax mixed infection. Results showed high polymorphisms in P. falciparum msp1, msp2 and glurp genes. Multiple infection rate was 28.6% [95% CI 12.2–52.3%]. The mean of MOI was 1.79 ± 0.74.

Conclusion

This pilot study highlighted that malaria diagnosis and molecular analysis are possible by using used malaria RDT. A large-scale study needs to be conducted to assess more comprehensively malaria parasites transmission levels and provide new data for guiding the implementation of local strategies for malaria control and elimination.

Trial registration Retrospectively registered

Plasmodium falciparum Clinical Isolates Reveal Analogous Circulation of 3D7 and FC27 Allelic Variants and Multiplicity of Infection in Urban and Rural Settings: The Case of Adama and Its Surroundings, Oromia, Ethiopia

Background

Despite significant progress achieved globally in reducing malaria burden, still it is one of the major public health and economic problems in Ethiopia. Investigation of the local genetic polymorphism of P. falciparum, the most virulent and predominant malaria parasite primarily targeted in malaria control and elimination program, is paramount to assess intensity of parasite transmission. Analysis of the block 3 region of the msp-2 gene of P. falciparum provides strong molecular evidence to evaluate the real picture of malaria epidemiology to fine-tune the ongoing control and elimination programs in the region. Thus, this study was aimed at examining the status of such polymorphic gene and its implications in Adama and its surroundings.

Methods

148 isolates from patients with uncomplicated falciparum malaria were collected in the study from September 2019 to August 2020. Tween® 20 and the Chelex method were employed for parasite DNA extraction. msp-2 allelic families were genotyped by using nested polymerase chain reaction targeting its 3D7 and FC27 allelic variants followed by gel electrophoresis for fragment analysis.

Results

Seventeen different polymorphic forms of msp-2 allelic fragments were detected in the study area. Moreover, 47 (31.8%) and 41(27.7%) were detected for 3D7 and FC27 allelic families, respectively. Furthermore, the multiclonal allele type accounted for 60 (40.5%). The mean MOI was 1.4, and the heterogeneity index (He) is 0.49 indicating nearly intermediate malaria transmission in the study area.

Conclusions

The study revealed nearly intermediate genetic diversity and mean MOI of P. falciparum in the study area, demanding further scale up of the ongoing control and elimination efforts.

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.

Trends and predictive factors for treatment failure following artemisinin-based combination therapy among children with uncomplicated malaria in Ghana: 2005-2018

BACKGROUND

Since the introduction of artemisinin-based combination therapy (ACT) in Ghana in 2005 there has been a surveillance system by the National Malaria Control Programme (NMCP) and the University of Ghana Noguchi Memorial Institute for Medical Research (UG-NMIMR) to monitor the therapeutic efficacy of ACTs for the treatment of uncomplicated malaria in the country. We report trends and determinants of failure following treatment of Ghanaian children with artesunate-amodiaquine (ASAQ) and artemether-lumefantrine (AL) combinations.

METHODS

Per protocol analyses as well as cumulative incidence of day 28 treatment failure from Kaplan Meier survival analyses were used to describe trends of failure over the surveillance period of 2005-2018. Univariable and multivariable cox regression analyses were used to assess the determinants of treatment failure over the period.

RESULTS

Day 28 PCR-corrected failure, following treatment with ASAQ, significantly increased from 0.0% in 2005 to 2.0% (95% CI: 1.1-3.6) in 2015 (p = 0.013) but significantly decreased to 0.4% (95% CI: 0.1-1.6) in 2018 (p = 0.039). Failure, following treatment with AL, decreased from 4.5% (95% CI: 2.0-9.4) in 2010 to 2.7% (95% CI: 1.4-5.1) in 2018, though not statistically significant (p = 0.426). Risk of treatment failure, from multivariable cox regression analyses, was significantly lower among children receiving ASAQ compared with those receiving AL (HR = 0.24; 95% CI: 0.11-0.53; p < 0.001); lower among children with no parasitaemia on day 3 compared with those with parasitaemia on day 3 (HR = 0.02; 95% CI: 0.01-0.13; p < 0.001); and higher among children who received ASAQ and had axillary temperature ≥ 37.5 °C on day 1 compared with those with axillary temperature < 37.5 °C (HR = 3.96; 95% CI: 1.61-9.75; p = 0.003).

CONCLUSIONS

Treatment failures for both ASAQ and AL have remained less than 5% (below WHO's threshold of 10%) in Ghana since 2005. Predictors of treatment failure that need to be considered in the management of uncomplicated malaria in the country should include type of ACT, day 3 parasitaemia, and day 1 axillary temperature of patients being treated.

The emergence of chloroquine-sensitive Plasmodium falciparum is influenced by selected communities in some parts of the Central Region of Ghana

Background

The return of chloroquine-sensitive Plasmodium falciparum in sub-Saharan Africa countries offers the opportunity for the reintroduction of chloroquine (CQ) either in combination with other drugs or as a single therapy for the management of malaria. This study assesses the influence of individual study sites on the selection of CQ sensitive P. falciparum markers in the Central region of Ghana.

Methods

Genomic DNA was extracted from an archived filter paper blood blot from Cape Coast, Elmina, Assin Fosu, and Twifo Praso using the Chelex DNA extraction method. The age metadata of the patients from whom the blood spots were taken was collected. The prevalence of CQ-sensitive markers of pfcrt K76 and pfmdr1 N86 was performed using nested PCR and RFLP. The data were analysed using Chi-square and Odd ratio.

Results

The overall prevalence of CQ-sensitive P. falciparum markers, pfcrt K76 and pfmdr1 N86 in the Central Region of Ghana were 142 out of 184 (77.17%) and 180 out of 184 (97.83%), respectively. The distribution of pfcrt K76 was assessed among the age groups per the individual study sites. 12 out of 33 (36.36%), 8 out of 33 (24.24%) and 6 out of 33 (18.18%) of pfcrt K76 CQ-sensitive marker were isolated from age 0 to 5 years, 16 to 30 years and 31 to 45 years old respectively at Cape Coast. Assin Fosu and Twifo Praso had the highest pfcrt K76 prevalence in 0–5 years, followed by 16–30 years and 6–15 years of age. The results showed that there was a significant prevalence of pfcrt K76 in all study sites; Cape Coast (χ² = 26.48, p < 0.0001), Assin Fosu (χ² = 37.67, p < 0.0001), Twifo Praso (χ² = 32.25, p < 0.0001) and Elmina (χ² = 17.88, p < 0.0001). Again, the likelihood to detect pfcrt K76 (OR (95% CI) was 7.105 (3.118–17.14), p < 0.0001 and pfmdr1 (2.028 (1.065–3.790), p < 0.001) among P. falciparum isolates from Cape Coast to be seven times and two times, respectively.

Conclusion

The study showed a significant selection and expansion of chloroquine-sensitive P. falciparum markers in all the selected study areas in the Central region. This finding has a significant implication for the future treatment, management, and control of P. falciparum malaria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03985-8.

The Use of Screening Algorithm to Defer Blood Donors with Subclinical Malaria

Plasmodium falciparum infection in blood donors is common in malaria endemic countries, including Ghana. To date, there are no established exclusion criteria to defer a donor carrying malaria parasites. Therefore, based on significant independent variables identified in this study, donor malaria screening algorithm was developed to be used by blood banks to screen blood donors for subclinical malaria. Each significant variable was weighted one (1) point and its alternative response was weighted negative one (-1) point. Accumulation of the points determines the risk level of the donor. These weighted points were used to categorize infected donors as having negligible (<2 points), tolerable (3-4 points), undesirable (5-8 points), or intolerable (>9 points) risk. Based on accumulated weight of ≥5 points, the algorithm was 94.7% (54/57) sensitive but 82% (298/364) specific. With this level of specificity, 18% of the blood donors without malaria would have been deferred. Therefore, it is imperative that all donors with accumulated risk ≥5 be screened for malaria using either malaria rapid test kit or microscopy.

Population structure and diversity of Plasmodium falciparum in children with asymptomatic malaria living in different ecological zones of Ghana

BACKGROUND

Genetic diversity in Plasmodium falciparum populations can be used to describe the resilience and spatial distribution of the parasite in the midst of intensified intervention efforts. This study used microsatellite analysis to evaluate the genetic diversity and population dynamics of P. falciparum parasites circulating in three ecological zones of Ghana.

METHODS

A total of 1168 afebrile children aged between 3 to 13 years were recruited from five (5) Primary schools in 3 different ecological zones (Sahel (Tamale and Kumbungu), Forest (Konongo) and Coastal (Ada and Dodowa)) of Ghana. Asymptomatic malaria parasite carriage was determined using microscopy and PCR, whilst fragment analysis of 6 microsatellite loci was used to determine the diversity and population structure of P. falciparum parasites.

RESULTS

Out of the 1168 samples examined, 16.1 and 39.5% tested positive for P. falciparum by microscopy and nested PCR respectively. The genetic diversity of parasites in the 3 ecological zones was generally high, with an average heterozygosity (He) of 0.804, 0.787 and 0.608 the rainy (peak) season for the Sahel, Forest and Coastal zones respectively. The mean He for the dry (off-peak) season were 0.562, 0.693 and 0.610 for the Sahel, Forest and Coastal zones respectively. Parasites from the Forest zone were more closely related to those from the Sahel than from the Coastal zone, despite the Coastal zone being closer in physical distance to the Forest zone. The fixation indexes among study sites ranged from 0.049 to 0.112 during the rainy season and 0.112 to 0.348 during the dry season.

CONCLUSION

A large asymptomatic parasite reservoir was found in the school children during both rainy and dry seasons, especially those in the Forest and Sahel savannah zones where parasites were also found to be related compared to those from the Coastal zone. Further studies are recommended to understand why despite the roll out of several malaria interventions in Ghana, high transmission still persist.

Implicating extracellular vesicles in Plasmodium falciparum artemisinin resistance development

Plasmodium falciparum malaria remains a disease of significant public health impact today. With the risk of emerging artemisinin resistance stalling malaria control efforts, the need to deepen our understanding of the parasite's biology is dire. Extracellular vesicles (EVs) are vital to the biology of P. falciparum and play a role in the pathogenesis of malaria. Recent studies have also shown that EVs may play a role in the development of artemisinin resistance in P. falciparum. Here, we highlight evidence on EVs in P. falciparum biology and malaria pathogenesis and argue that there is sufficient ground to propose a role for EVs in the development of P. falciparum artemisinin resistance. We suggest that EVs are actively secreted functional organelles that contribute to cellular homeostasis in P. falciparum-infected red blood cells under artemisinin pressure. Further exploration of this hypothesized EVs-based molecular mechanism of artemisinin resistance will aid the discovery of novel antimalarial therapies.

Evolution of Antimalarial Drug Resistance Markers in the Reservoir of Plasmodium falciparum Infections in the Upper East Region of Ghana

BACKGROUND

The majority of Plasmodium falciparum infections, constituting the reservoir in all ages, are asymptomatic in high-transmission settings in Africa. The role of this reservoir in the evolution and spread of drug resistance was explored.

METHODS

Population genetic analyses of the key drug resistance-mediating polymorphisms were analyzed in a cross-sectional survey of asymptomatic P. falciparum infections across all ages in Bongo District, Ghana.

RESULTS

Seven years after the policy change to artemisinin-based combination therapies in 2005, the pfcrt K76 and pfmdr1 N86 wild-type alleles have nearly reached fixation and have expanded via soft selective sweeps on multiple genetic backgrounds. By constructing the pfcrt-pfmdr1-pfdhfr-pfdhps multilocus haplotypes, we found that the alleles at these loci were in linkage equilibrium and that multidrug-resistant parasites have not expanded in this reservoir. For pfk13, 32 nonsynonymous mutations were identified; however, none were associated with artemisinin-based combination therapy resistance.

CONCLUSIONS

The prevalence and selection of alleles/haplotypes by antimalarials were similar to that observed among clinical cases in Ghana, indicating that they do not represent 2 subpopulations with respect to these markers. Thus, the P. falciparum reservoir in all ages can contribute to the maintenance and spread of antimalarial resistance.

Impact of an Irrigation Dam on the Transmission and Diversity of Plasmodium falciparum in a Seasonal Malaria Transmission Area of Northern Ghana

Water bodies such as dams are known to alter the local transmission patterns of a number of infectious diseases, especially those transmitted by insects and other arthropod vectors. The impact of an irrigation dam on submicroscopic asexual parasite carriage in individuals living in a seasonal malaria transmission area of northern Ghana was investigated. A total of 288 archived DNA samples from two cross-sectional surveys in two communities in the Bongo District of Northern Ghana were analysed. Parasite density was determined by light microscopy and PCR, and parasite diversity was assessed by genotyping of the polymorphic Plasmodium falciparum msp2 block-3 region. Submicroscopic parasitaemia was estimated as the proportional difference between positive samples identified by PCR and microscopy. Dry season submicroscopic parasite prevalence was significantly higher (71.0%, p=0.013) at the dam site compared with the nondam site (49.2%). Similarly, wet season submicroscopic parasite prevalence was significantly higher at the dam site (54.5%, p=0.008) compared with the nondam site (33.0%). There was no difference in parasite density between sites in the dry season (p=0.90) and in the wet season (p=0.85). Multiplicity of infection (MOI) based on PCR data was significantly higher at the dam site compared with the nondam site during the dry season (p < 0.0001) but similar between sites during the wet season. MOI at the nondam site was significantly higher in the wet season than in the dry season (2.49, 1.26, p < 0.0001) but similar between seasons at the dam site. Multivariate analysis showed higher odds of carrying submicroscopic parasites at the dam site in both dry season (OR = 7.46, 95% CI = 3.07–18.15) and in wet season (OR = 1.73, 95% CI = 1.04–2.86). The study findings suggest that large water bodies impact year-round carriage of submicroscopic parasites and sustain Plasmodium transmission.

Plasmodium falciparum Kelch Propeller Polymorphisms in Clinical Isolates from Ghana from 2007 to 2016

The continuous surveillance of polymorphisms in the kelch propeller domain of Plasmodium falciparum from Africa is important for the discovery of the actual markers of artemisinin resistance in the region. The information on the markers is crucial for control strategies involving chemotherapy and chemoprophylaxis for residents and nonimmune travelers to the country. Polymorphisms in the kelch propeller domain of Ghanaian malaria parasites from three different ecological zones at several time periods were assessed. A total of 854 archived samples (2007 to 2016) collected from uncomplicated malaria patients aged ≤9 years old from 10 sentinel sites were used. Eighty-four percent had wild-type sequences (PF3D7_1343700), while many of the mutants had mostly nonsynonymous mutations clustered around codons 404 to 650. Variants with different amino acid changes of the codons associated with artemisinin (ART) resistance validated markers were observed in Ghanaian isolates: frequencies for I543I, I543S, I543V, R561P, R561R, and C580V were 0.12% each and 0.6% for R539I. Mutations reported from African parasites, A578S (0.23%) and Q613L (0.23%), were also observed. Three persisting nonsynonymous (NS) mutations, N599Y (0.005%), K607E (0.004%), and V637G (0.004%), were observed in 3 of the 5 time periods nationally. The presence of variants of the validated markers of artemisinin resistance as well as persisting polymorphisms after 14 years of artemisinin-based combination therapy use argues for continuous surveillance of the markers. The molecular markers of artemisinin resistance and the observed variants will be monitored subsequently as part of ongoing surveillance of antimalarial drug efficacy/resistance studies in the country.

The Diversity, Multiplicity of Infection and Population Structure of P. falciparum Parasites Circulating in Asymptomatic Carriers Living in High and Low Malaria Transmission Settings of Ghana

Background: Diversity in Plasmodium falciparum poses a major threat to malaria control and elimination interventions. This study utilized 12 polymorphic microsatellite (MS) markers and the Msp2 marker to examine diversity, multiplicity of infection (MOI) as well as the population structure of parasites circulating in two sites separated by about 92 km and with varying malaria transmission intensities within the Greater Accra Region of Ghana. Methods: The diversity and MOI of P. falciparum parasites in 160 non-symptomatic volunteers living in Obom (high malaria transmission intensity) and Asutsuare (low malaria transmission intensity) aged between 8 and 60 years was determined using Msp2 genotyping and microsatellite analysis. Results: The prevalence of asymptomatic P. falciparum carriers as well as the parasite density of infections was significantly higher in Obom than in Asutsuare. Samples from Asutsuare and Obom were 100% and 65% clonal, respectively, by Msp2 genotyping but decreased to 50% and 5%, respectively, when determined by MS analysis. The genetic composition of parasites from Obom and Asutsuare were highly distinct, with parasites from Obom being more diverse than those from Asutsuare. Conclusion: Plasmodium falciparum parasites circulating in Obom are genetically more diverse and distinct from those circulating in Asutsuare. The MOI in samples from both Obom and Asutsuare increased when assessed by MS analysis relative to MSP2 genotyping. The TA40 and TA87 loci are useful markers for estimating MOI in high and low parasite prevalence settings.

Low genetic diversity and complexity of submicroscopic Plasmodium falciparum infections among febrile patients in low transmission areas in Senegal

INTRODUCTION

Submicroscopic Plasmodium infections are common in malaria endemic countries, but very little studies have been done in Senegal. This study investigates the genetic diversity and complexity of submicroscopic P. falciparum infections among febrile patients in low transmission areas in Senegal.

MATERIALS AND METHODS

Hundred and fifty blood samples were collected from febrile individuals living in Dielmo and Ndiop (Senegal) between August 2014 and January 2015, tested for microscopic and sub-microscopic P. falciparum infections and characterized for their genetic diversity and complexity of infections using msp-1 and msp-2 genotyping.

RESULTS

Submicroscopic P. falciparum infections were 19.6% and 25% in Dielmo and Ndiop, respectively. K1 and 3D7 were the predominant msp-1 and msp-2 allelic types with respective frequencies of 67.36% and 67.10% in microscopic isolates and 58.24% and 78% in submicroscopic ones. Frequencies of msp-1 allelic types were statistically comparable between the studied groups (p>0.05), and were respectively 93.54% vs 87.5% for K1, 60% vs 54.83% for MAD20 and 41.93% vs 22.5% for RO33 while frequencies of msp-2 allelic types were significantly highest in the microscopy group for FC27 (41.93% vs 10%, Fisher's Exact Test, p = 0.001) and 3D7 (61.29% vs 32.5%, Fisher's Exact Test, p = 0.02). Multiplicities of infection were lowest in submicroscopic P. falciparum isolates.

CONCLUSIONS

The study revealed a high submicroscopic P. falciparum carriage among patients in the study areas, and that submicroscopic P. falciparum isolates had a lower genetic diversity and complexity of malaria infections.

Genetic diversity and allele frequencies of Plasmodium falciparum msp1 and msp2 in parasite isolates from Bioko Island, Equatorial Guinea

BACKGROUND

Malaria is still a serious public health problem on Bioko Island (Equatorial Guinea), although the number of annual cases has been greatly reduced since 2004 through the Bioko Island Malaria Control Project (BIMCP). A better understanding of malaria parasite population diversity and transmission dynamics is critical for assessing the effectiveness of malaria control measures. The objective of this study is to investigate the genetic diversity of Plasmodium falciparum populations and multiplicity of infection (MOI) on Bioko Island 7 years after BIMCP.

METHODS

A total of 181 patients with uncomplicated P. falciparum malaria diagnosed with microscopy were collected from Bioko Island from January 2011 to December 2014. Parasite DNA was extracted using chelex-100 and species were identified using a real-time PCR followed by high-resolution melting. Plasmodium falciparum msp1 and msp2 allelic families were determined using nested PCR.

RESULTS

Three msp1 alleles (K1, MAD20, and RO33) and two msp2 alleles (FC27 and 3D7) were analysed in all samples. In msp1, the MAD20 allelic family was predominant with 96.69% (175/178) followed respectively by the K1 allelic family with 96.07% (171/178) and R033 allelic family with 70.78% (126/178). In msp2, the FC27 allelic family was the most frequently detected with 97.69% (169/173) compared to 3D7 with 72.25% (125/173). Twenty-six different alleles were observed in msp1 with 9 alleles for K1, 9 alleles for MAD20 and 8 alleles for R033. In msp2, 25 individual alleles were detected with 5 alleles for FC27 and 20 alleles for 3D7. The overall MOI was 5.51 with respectively 3.5 and 2.01 for msp1 and msp2. A significant increase in overall MOI was correlated with the age group of the patients (P = 0.026) or parasite densities (P = 0.04).

CONCLUSIONS

The present data showed high genetic diversity and MOI values among the P. falciparum population in the study, reflecting both the high endemic level and malaria transmission on Bioko Island. These data provide valuable information for surveillance of P. falciparum infection and for assessing the appropriateness of the current malarial control strategies in the endemic area.

The prevalence of submicroscopic Plasmodium falciparum gametocyte carriage and multiplicity of infection in children, pregnant women and adults in a low malaria transmission area in Southern Ghana

BACKGROUND

The gametocyte stage of Plasmodium falciparum is considered an important target for disrupting malaria transmission. Indications are that various demographic groups, such as children and pregnant women may differ in risk of harbouring gametocytes, which may be crucial for targeted control. In this study, the relationship between the prevalence and multiplicity of P. falciparum, asexual parasite infections and gametocytaemia was assessed in three different demographic groups in an area of southern Ghana with low malaria endemicity. Levels of antibody responses to Pfs230 were also assessed as a proxy for the presence of gametocytes.

METHODS

The study involved multiple cross-sectional sampling of children (N = 184, aged 2-15 years), male and non-pregnant female adults (N = 154, aged 16-65 years) and pregnant women (N = 125, aged 18-45 years) from Asutsuare in the Shai Osudoku District of Greater Accra Region in Ghana. Asexual parasitaemia was detected by microscopy and PCR, and gametocytaemia was assessed by Pfs25-real time PCR. Multiclonal P. falciparum infections were estimated by msp2 genotyping and an indirect ELISA was used to measure plasma IgG antibodies to Pfs230 antigen.

RESULTS

Overall, children and pregnant women had higher prevalence of submicroscopic gametocytes (39.5% and 29.7%, respectively) compared to adults (17.4%). Multiplicity of infection observed amongst children (3.1) and pregnant women (3.9) were found to be significantly higher (P = 0.006) compared with adults (2.7). Risk of gametocyte carriage was higher in individuals infected with P. falciparum having both Pfmsp2 3D7 and FC27 parasite types (OR = 5.92, 95% CI 1.56-22.54, P = 0.009) compared with those infected with only 3D7 or FC27 parasite types. In agreement with the parasite prevalence data, anti-Pfs230 antibody levels were lower in gametocyte positive adults (β = - 0.57, 95% CI - 0.81, - 0.34, P < 0.001) compared to children.

CONCLUSIONS

These findings suggest that children and pregnant women are particularly important as P. falciparum submicroscopic gametocyte reservoirs and represent important focus groups for control interventions. The number of clones increased in individuals carrying gametocytes compared to those who did not carry gametocytes. The higher anti-gametocyte antibody levels in children suggests recent exposure and may be a marker of gametocyte carriage.

Seasonal variations in Plasmodium falciparum genetic diversity and multiplicity of infection in asymptomatic children living in southern Ghana

Background

Genetic diversity in Plasmodium falciparum (P. falciparum) parasites is a major hurdle to the control of malaria. This study monitored changes in the genetic diversity and the multiplicity of P. falciparum parasite infection in asymptomatic children living in southern Ghana at 3 month intervals between April 2015 and January 2016.

Methods

Filter paper blood spots (DBS) were collected quarterly from children living in Obom, a community with perennial malaria transmission and Abura, a community with seasonal malaria transmission. Genomic DNA was extracted from the DBS and used in polymerase chain reaction (PCR)-based genotyping of the merozoite surface protein 1 (msp 1) and merozoite surface protein 2 (msp 2) genes.

Results

Out of a total of 787 samples that were collected from the two study sites, 59.2% (466/787) tested positive for P. falciparum. The msp 1 and msp 2 genes were successfully amplified from 73.8% (344/466) and 82.5% (385/466) of the P. falciparum positive samples respectively. The geometric mean MOI in Abura ranged between 1.17 (95% CI: 1.08–1.28) and 1.48 (95% CI: 1.36–1.60) and was significantly lower (p < 0.01, Dunn’s multiple comparison test) than that determined in Obom, where the geometric mean MOI ranged between 1.82 (95% CI: 1.58–2.08) and 2.50 (95% CI: 2.33–2.678) over the study period. Whilst the msp 1 R033:MAD20:KI allelic family ratio was dynamic, the msp 2 3D7:FC27 allelic family ratio remained relatively stable across the changing seasons in both sites.

Conclusions

This study shows that seasonal variations in parasite diversity in these communities can be better estimated by msp 1 rather than msp 2 due to the constantly changing relative intra allelic frequencies observed in msp 1 and the fact that the dominance of any msp 2 allele was dependent on the transmission setting but not on the season as opposed to the dominance of any msp 1 allele, which was dependent on both the season and the transmission setting.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3350-z) contains supplementary material, which is available to authorized users.

Temporal changes in genetic diversity of msp-1, msp-2, and msp-3 in Plasmodium falciparum isolates from Grande Comore Island after introduction of ACT

Background

Malaria is still one of the serious public health problems in Grande Comore Island, although the number of annual cases has been greatly reduced in recent years. A better understanding of malaria parasite population diversity and transmission dynamics is critical for assessing the effectiveness of malaria control measures. The objective of this study is to investigate temporal changes in genetic diversity of Plasmodium falciparum populations and multiplicity of infection (MOI) in Grande Comore 10 years after introduction of ACT.

Methods

A total of 232 P. falciparum clinical isolates were collected from the Grande Comore Island during two sampling periods (118 for 2006‒2007 group, and 114 for 2013‒2016 group). Parasite isolates were characterized for genetic diversity and complexity of infection by genotyping polymorphic regions in merozoite surface protein gene 1 (msp-1), msp-2, and msp-3 using nested PCR and DNA sequencing.

Results

Three msp-1 alleles (K1, MAD20, and RO33), two msp-2 alleles (FC27 and 3D7), and two msp-3 alleles (K1 and 3D7) were detected in parasites of both sampling periods. The RO33 allele of msp-1 (84.8%), 3D7 allele of msp-2 (90.8%), and K1 allele of msp-3 (66.7%) were the predominant allelic types in isolates from 2006–2007 group. In contrast, the RO33 allele of msp-1 (63.4%), FC27 allele of msp-2 (91.1%), and 3D7 allele of msp-3 (53.5%) were the most prevalent among isolates from the 2013–2016 group. Compared with the 2006‒2007 group, polyclonal infection rates of msp-1 (from 76.7 to 29.1%, P < 0.01) and msp-2 (from 62.4 to 28.3%, P < 0.01) allelic types were significantly decreased in those from 2013‒2016 group. Similarly, the MOIs for both msp-1 and msp-2 were higher in P. falciparum isolates in the 2006–2007 group than those in 2013–2016 group (MOI = 3.11 vs 1.63 for msp-1; MOI = 2.75 vs 1.35 for msp-2). DNA sequencing analyses also revealed reduced numbers of distinct sequence variants in the three genes from 2006‒2007 to 2013‒2016: msp-1, from 32 to 23 (about 28% decline); msp-2 from 29 to 21 (about 28% decline), and msp-3 from 11 to 3 (about 72% decline).

Conclusions

The present data showed dramatic reduction in genetic diversity and MOI among Grande Comore P. falciparum populations over the course of the study, suggesting a trend of decreasing malaria transmission intensity and genetic diversity in Grande Comore Island. These data provide valuable information for surveillance of P. falciparum infection and for assessing the appropriateness of the current malarial control strategies in the endemic area.

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.

Plasmodium reichenowi EBA-140 merozoite ligand binds to glycophorin D on chimpanzee red blood cells, shedding new light on origins of Plasmodium falciparum

Background

All symptoms of malaria are caused by the intraerythrocytic proliferation of Plasmodium merozoites. Merozoites invade erythrocytes using multiple binding ligands that recognise specific surface receptors. It has been suggested that adaptation of Plasmodium parasites to infect specific hosts is driven by changes in genes encoding Plasmodium erythrocyte-binding ligands (EBL) and reticulocyte-binding ligands (RBL). Homologs of both EBL and RBL, including the EBA-140 merozoite ligand, have been identified in P. falciparum and P. reichenowi, which infect humans and chimpanzees, respectively. The P. falciparum EBA-140 was shown to bind human glycophorin C, a minor erythrocyte sialoglycoprotein. Until now, the erythrocyte receptor for the P. reichenowi EBA-140 remained unknown.

Methods

The baculovirus expression vector system was used to obtain the recombinant EBA-140 Region II, and flow cytometry and immunoblotting methods were applied to characterise its specificity.

Results

We showed that the chimpanzee glycophorin D is the receptor for the P. reichenowi EBA-140 ligand on chimpanzee red blood cells.

Conclusions

We propose that the development of glycophorin C specificity is spurred by the P. falciparum lineage. We speculate that the P. falciparum EBA-140 evolved to hijack GPC on human erythrocytes during divergence from its ape ancestor.

Natural antibody responses to Plasmodium falciparum MSP3 and GLURP(R0) antigens are associated with low parasite densities in malaria patients living in the Central Region of Ghana

Background

Plasmodium falciparum genetic diversity and multiplicity of infection (MOI) are parasite features that have been suggested to influence the acquisition of protective immunity against malaria. This study sought to assess the relationship between MOI and parasite density (PD) in malaria patients living in the Central Region of Ghana and to determine whether naturally occurring antibody levels against P. falciparum GLURP (PF3D7_1035300) and MSP3 (PF3D7_1035400) antigens are associated with decreased parasite load.

Methods

Dried filter paper blood blots were obtained from children and adults diagnosed with uncomplicated P. falciparum malaria. Microscopy was used to estimate P. falciparum parasite density and polymerase chain reaction (PCR) amplification of the polymorphic regions of msp1 (PF3D7_0930300) and msp2 (PF3D7_0206800) was used for parasite genotyping and MOI determination. ELISA was used to measure the serum IgG concentration of R0 fragment of GLURP (GLURP(R0)) and MSP3 antibodies.

Results

All 115 samples were positive for P. falciparum by PCR using either the msp1 or msp2 genotyping primer sets. The most prevalent msp1 and msp2 alleles were KI and 3D7, respectively. The geometric mean (GM) for MOI determined by both msp1 and msp2 genotyping was 1.3 for the entire population and was generally higher in children than in adults. Seropositivity was estimated at 67 and 63% for GLURP(R0) and MSP3 antibodies, respectively, and antibody titers were negatively correlated with parasite density.

Conclusions

The negative correlation between naturally occurring GLURP(R0) and MSP3 antibody levels and parasite density observed in this study suggest that augmenting the antibody response with the GMZ2 vaccine could enhance protection in the Central Region of Ghana.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2338-7) contains supplementary material, which is available to authorized users.

Plasmodium falciparum genotype and gametocyte prevalence in children with uncomplicated malaria in coastal Ghana

BACKGROUND

Plasmodium falciparum gametocytes are vital to sustaining malaria transmission. Parasite densities, multiplicity of infection as well as asexual genotype are features that have been found to influence gametocyte production. Measurements of the prevalence of Plasmodium sp. gametocytes may serve as a tool to monitor the success of malaria eradication efforts.

METHODS

Whole blood was collected from 112 children aged between 6 months and 13 years with uncomplicated P. falciparum malaria attending three health facilities in southern Ghana from June to August, 2014 before (day 0) and 4 days after completion of anti-malaria drug treatment (day 7). Malaria parasites were observed by microscopy and polymerase chain reaction (PCR); submicroscopic gametocyte carriage was measured by a Pfs25 (PF3D7_1031000) mRNA real time reverse transcriptase polymerase chain reaction (RT-PCR). Parasite genotyping was performed on gDNA extracted from dried filter paper blood blots by amplification of the polymorphic regions of msp1 (PF3D7_0930300) and msp2 (PF3D7_0206800) using PCR.

RESULTS

Microscopy estimated 3.1% (3/96) of the total population to carry gametocytes on day 0, which decreased to 2.1% (2/96) on day 7. In contrast, reverse transcriptase-real time PCR (RT-PCR) analysis of a subset of 35 samples estimated submicroscopic gametocyte carriage to be as high as 77% (27/35) using primers specific for Pfs25 (CT < 35) on day 0 and by day 7 this only declined to 60% (21/35). Genotyping the msp2 gene identified higher levels of MOI than the msp1 gene.

CONCLUSIONS

Although below detection by microscopy, gametocyte prevalence at submicroscopic levels are high in this region and emphasize the need for more effective elimination approaches like the development of transmission-blocking vaccines and safer gametocytocidal drugs.