Asymptomatic Plasmodium Infections in Children in Low Malaria Transmission Setting, Southwestern Uganda(1)

Non-falciparum malaria infections in Uganda, does it matter? A review of the published literature

BACKGROUND

Plasmodium falciparum is the dominant malaria species in the sub-Saharan Africa and the main cause of severe disease and death. Notwithstanding, severe malaria and death due to non-falciparum infections have been reported, but at much lower rates than P. falciparum infections. Following increasing use of molecular detection techniques in epidemiological studies, a higher prevalence of non-falciparum species has been reported in the region than previously thought. This article reviews the literature on the prevalence of non-falciparum malaria species in Uganda and the clinical figures of their severe diseases. It aims to elucidate the extent to which mono non-falciparum malaria infections in a highly malaria-endemic country contribute to malaria mortality and outline its policy implications on malaria case management.

METHODS

The available English-language published peer-reviewed literature up to March 2024 was sought via PubMed and Google Scholar. The keywords used were severe malaria, AND P. falciparum, P. malariae, P. vivax, P. ovale spp., mixed infections AND Uganda. The review encompassed 53 articles. Articles using molecular diagnosis methods were accounted for analysis.

RESULTS

The literature reported a substantial prevalence of non-falciparum infections in Uganda. Plasmodium malariae and Plasmodium ovale spp. were the second and third most prevalent reported malaria species respectively after P. falciparum as dominant species. Non-falciparum malaria infections often occur as mixed infections rather than mono-infections. Besides, molecular diagnostics revealed that 21% of initially reported mono-infections of P. falciparum were, in fact, mixed infections. No article was found on the prevalence of severe malaria or case fatality rate due to mixed or non-falciparum infections.

CONCLUSION

A critical knowledge gap exists regarding the impact of mixed and non-falciparum species on severe malaria and death in Uganda. Robust evidence on prevalence, recurrent parasitaemia, and severe clinical manifestations of mixed and non-falciparum malaria infections is crucial for evidence-based and effective policymaking regarding malaria case management.

Assessing the daily natural history of asymptomatic Plasmodium infections in adults and older children in Katakwi, Uganda: a longitudinal cohort study

BACKGROUND

Low-density asymptomatic Plasmodium infections are prevalent in endemic areas, but little is known about their natural history. The trajectories of these infections and their propensity to fluctuate to undetectable densities can affect detection in clinical trials and field studies. We aimed to classify the natural history of these infections in a high transmission area over 29 days.

METHODS

In this longitudinal cohort study, we enrolled healthy, malaria-asymptomatic, afebrile, adults (age 18-59 years) and older children (age 8-17 years) in Katakwi District, Uganda, who were negative for Plasmodium infection on rapid diagnostic tests. Participants were instructed to self-collect one dried blood spot (DBS) per day for a maximum of 29 days. We excluded people if they were pregnant or taking antimalarials. During weekly clinic visits, staff collected a DBS and a 4 mL sample of venous blood. We analysed DBSs by Plasmodium 18S rRNA quantitative RT-PCR (qRT-PCR). We classified DBS by infection type as negative, P falciparum, non-P falciparum, or mixed. We plotted infection type over time for each participant and categorised trajectories as negative, new, cleared, chronic, or indeterminate infections. To estimate the effect of single timepoint sampling, we calculated the daily prevalence for each study day and estimated the number of infections that would have been detected in our population if sampling frequency was reduced.

FINDINGS

Between April 9 and May 20, 2021, 3577 DBSs were collected by 128 (40 male adults, 60 female adults, 12 male children, and 16 female children) study participants. 2287 (64%) DBSs were categorised as negative, 751 (21%) as positive for P falciparum, 507 (14%) as positive for non-P falciparum, and 32 (1%) as mixed infections. Daily Plasmodium prevalence in the population ranged from 45·3% (95% CI 36·6-54·1) at baseline to 30·3% (21·9-38·6) on day 24. 37 (95%) of 39 P falciparum and 35 (85%) of 41 non-P falciparum infections would have been detected with every other day sampling, whereas, with weekly sampling, 35 (90%) P falciparum infections and 31 (76%) non-P falciparum infections would have been detected.

INTERPRETATION

Parasite dynamics and species are highly variable among low-density asymptomatic Plasmodium infections. Sampling every other day or every 3 days detected a similar proportion of infections as daily sampling, whereas testing once per week or even less frequently could misclassify up to a third of the infections. Even using highly sensitive diagnostics, single timepoint testing might misclassify the true infection status of an individual.

FUNDING

US National Institutes of Health and Bill and Melinda Gates Foundation.

Prevalence and factors associated with malaria, typhoid, and co-infection among febrile children aged six months to twelve years at kampala international university teaching hospital in western Uganda

Background

Paediatric febrile illnesses pose diagnostic challenges in low-income countries. Western Uganda is endemic for both malaria and typhoid but the true prevalence of each individual disease, their co-infections and associated factors are poorly quantified.

Objective

To determine the prevalence of malaria, typhoid, their co-infection, and associated factors amongst febrile children attending the paediatrics and child health department of Kampala International University Teaching Hospital (KIU-TH) in Western Uganda.

Methods

Cross-sectional study used a survey questionnaire covering demographics, clinical and behavioural variables. We obtained blood for peripheral films for malaria and cultures for typhoid respectively; from 108 consecutively consented participants. Ethical approval was obtained from KIU-TH research and ethics committee (No. UG-REC-023/201,834). Multivariate regression analysis was performed using Stata 14.0 (StataCorp. 2015) at 95% confidence interval, regarding p < 0.05 as statistically significant.

Results

Majority of participants were males 62% (n = 67), cared for by their mothers 86.1% (n = 93). The prevalence of malaria was 25% (n = 27). The prevalence of typhoid was 3.7% (n = 4), whereas the prevalence of malaria-typhoid co-infection was 2.8% (n = 3). Using treated water from protected public taps was associated with low malaria-typhoid co-infection [p = 0.04; aOR = 0.05, 95%CI [0.003-0.87], whereas drinking unboiled water from open wells increased the risk for the co-infection [p = 0.037, cOR = 17, 95%CI (1.19-243.25)].

Conclusions

The prevalence of blood culture confirmed malaria-typhoid co-infection in children was lower than previously reported in serological studies. These findings emphasize the need to use gold standard diagnostic investigations in epidemiological studies. Educational campaigns should focus on the use of safe water, hygienic hand washing, and proper waste disposal; and should target mothers who mainly take care of these children.

Striving towards true equity in global health: A checklist for bilateral research partnerships

Interest in "global health" among schools of medicine, public health, and other health disciplines in high-income countries (HIC) continues to rise. Persistent power imbalances, racism, and maintenance of colonialism/neocolonialism plague global health efforts, including global health scholarship. Scholarly projects conducted in low- and middle-income countries (LMIC) by trainees at these schools in HIC often exacerbate these problems. Drawing on published literature and shared experiences, we review key inequalities within each phase of research, from design through implementation and analysis/dissemination, and make concrete and practical recommendations to improve equity at each stage. Key problems facing global health scholarship include HIC-centric nature of global health organizations, paucity of funding directly available for LMIC investigators and trainees, misplaced emphasis on HIC selected issues rather than local solutions to local problems, the dominance of English language in the scientific literature, and exploitation of LMIC team members. Four key principles lie at the foundation of all our recommendations: 1) seek locally derived and relevant solutions to global health issues, 2) create paired collaborations between HIC and LMIC institutions at all levels of training, 3) provide funding for both HIC and LMIC team members, 4) assign clear roles and responsibilities to value, leverage, and share the strengths of all team members. When funding for global health research is predicated upon more ethical and equitable collaborations, the nature of global health collaborations will evolve to be more ethical and equitable. Therefore, we propose the Douala Equity Checklist as a 20-item tool HIC and LMIC institutions can use throughout the conduct of global health projects to ensure more equitable collaborations.

Surveillance of Plasmodium falciparum pfcrt haplotypes in southwestern uganda by high-resolution melt analysis

BACKGROUND

Chloroquine (CQ) resistance is conferred by mutations in the Plasmodium falciparum CQ resistance transporter (pfcrt). Following CQ withdrawal for anti-malarial treatment, studies across malaria-endemic countries have shown a range of responses. In some areas, CQ sensitive parasites re-emerge, and in others, mutant haplotypes persist. Active surveillance of resistance mutations in clinical parasites is essential to inform treatment regimens; this effort requires fast, reliable, and cost-effective methods that work on a variety of sample types with reagents accessible in malaria-endemic countries.

METHODS

Quantitative PCR followed by High-Resolution Melt (HRM) analysis was performed in a field setting to assess pfcrt mutations in two groups of clinical samples from Southwestern Uganda. Group 1 samples (119 in total) were collected in 2010 as predominantly Giemsa-stained slides; Group 2 samples (125 in total) were collected in 2015 as blood spots on filter paper. The Rotor-Gene Q instrument was utilized to assess the impact of different PCR-HRM reagent mixes and the detection of mixed haplotypes present in the clinical samples. Finally, the prevalence of the wild type (CVMNK) and resistant pfcrt haplotypes (CVIET and SVMNT) was evaluated in this understudied Southwestern region of Uganda.

RESULTS

The sample source (i.e. Giemsa-stained slides or blood spots) and type of LCGreen-based reagent mixes did not impact the success of PCR-HRM. The detection limit of 10- 5 ng and the ability to identify mixed haplotypes as low as 10 % was similar to other HRM platforms. The CVIET haplotype predominated in the clinical samples (66 %, 162/244); however, there was a large regional variation between the sample groups (94 % CVIET in Group 1 and 44 % CVIET in Group 2).

CONCLUSIONS

The HRM-based method exhibits the flexibility required to conduct reliable assessment of resistance alleles from various sample types generated during the clinical management of malaria. Large regional variations in CQ resistance haplotypes across Southwestern Uganda emphasizes the need for continued local parasite genotype assessment to inform anti-malarial treatment policies.

Plasmodium malariae, current knowledge and future research opportunities on a neglected malaria parasite species

Plasmodium malariae is often reported as a benign malaria parasite. There are limited data on its biology and disease burden in sub-Saharan Africa (sSA) possibly due to the unavailability of specific and affordable tools for routine diagnosis and large epidemiology studies. In addition, P. malariae occurs at low parasite densities and in co-infections with other species, predominately P. falciparum. The paucity of data on P. malariae infections limits the capacity to accurately determine its contribution to malaria and the effect of control interventions against P. falciparum on its prevalence. Here, we summarise the current knowledge on P. malariae epidemiology in sSA - overall prevalence ranging from 0-32%, as detected by different diagnostic methods; seroprevalence ranging from 0-56% in three countries (Mozambique, Benin and Zimbabwe), and explore the future application of next-generation sequencing technologies as a tool for enriching P. malariae genomic epidemiology. This will provide insights into important adaptive mechanisms of this neglected non-falciparum species, including antimalarial drug resistance, local and regional parasite transmission patterns and genomic signatures of selection. Improved diagnosis and genomic surveillance of non-falciparum malaria parasites in Africa would be helpful in evaluating progress towards elimination of all human Plasmodium species.

Poor-quality antimalarials further health inequities in Uganda

Substandard and falsified medications are a major threat to public health, directly increasing the risk of treatment failure, antimicrobial resistance, morbidity, mortality and health expenditures. While antimalarial medicines are one of the most common to be of poor quality in low- and middle-income countries, their distributional impact has not been examined. This study assessed the health equity impact of substandard and falsified antimalarials among children under five in Uganda. Using a probabilistic agent-based model of paediatric malaria infection (Substandard and Falsified Antimalarial Research Impact, SAFARI model), we examine the present day distribution of the burden of poor-quality antimalarials by socio-economic status and urban/rural settings, and simulate supply chain, policy and patient education interventions. Patients incur US$26.1 million (7.8%) of the estimated total annual economic burden of substandard and falsified antimalarials, including $2.3 million (9.1%) in direct costs and $23.8 million (7.7%) in productivity losses due to early death. Poor-quality antimalarials annually cost $2.9 million to the government. The burden of the health and economic impact of malaria and poor-quality antimalarials predominantly rests on the poor (concentration index −0.28) and rural populations (98%). The number of deaths among the poorest wealth quintile due to substandard and falsified antimalarials was 12.7 times that of the wealthiest quintile, and the poor paid 12.1 times as much per person in out-of-pocket payments. Rural populations experienced 97.9% of the deaths due to poor-quality antimalarials, and paid 10.7 times as much annually in out-of-pocket expenses compared with urban populations. Our simulations demonstrated that interventions to improve medicine quality could have the greatest impact at reducing inequities, and improving adherence to antimalarials could have the largest economic impact. Substandard and falsified antimalarials have a significant health and economic impact, with greater burden of deaths, disability and costs on poor and rural populations, contributing to health inequities in Uganda.

Malaria elimination in Bhutan: asymptomatic malaria cases in the Bhutanese population living in malaria-risk areas and in migrant workers from India

In 2018, Bhutan reported 54 cases of malaria, of which six were indigenous, 14 introduced and 34 imported. Considering the continuous reduction in the number of indigenous cases, Bhutan plans to eliminate malaria by 2025 under the Bhutan Malaria Elimination Strategy. The study was conducted to assess the presence of asymptomatic plasmodial infection in both, Bhutanese population living in malaria-risk areas and in migrant workers to guide the elimination strategies. A cross-sectional study was conducted from April to May 2016 in 750 Bhutanese people and 473 migrant workers. Plasmodium falciparum and Plasmodium vivax infections were investigated by using a rapid diagnostic test (RDT) and the polymerase chain reaction (PCR). Prevalence of asymptomatic plasmodial infection based on PCR was 0.27% (95% CI: 0.05–1.07%) among Bhutanese people with a mean age of 43 years old. The proportions of males and females were 45% and 55%, respectively. Among migrant workers, the prevalence of asymptomatic plasmodial infection was 0.42% (95% CI: 0.07–1.69%) with a mean age of 30 years old. The majority of migrant workers were from the neighboring Indian State of West Bengal (57.51%), followed by Assam (12.26%). RDT in both study groups did not detect any plasmodial infection. The presence of a low prevalence of asymptomatic plasmodial infection indicates that the current elimination strategies and interventions are effective.

A Systematic Review: Performance of Rapid Diagnostic Tests for the Detection of Plasmodium knowlesi, Plasmodium malariae, and Plasmodium ovale Monoinfections in Human Blood

Background

Despite the increased use and worldwide distribution of malaria rapid diagnostic tests (RDTs) that distinguish between Plasmodium falciparum and non-falciparum species, little is known about their performance detecting Plasmodium knowlesi (Pk), Plasmodium malariae (Pm), and Plasmodium ovale (Po). This review seeks to analyze the results of published studies evaluating the diagnostic accuracy of malaria RDTs in detecting Pk, Pm, and Po monoinfections.

Methods

MEDLINE, EMBASE, Web of Science, and CENTRAL databases were systematically searched to identify studies that reported the performance of RDTs in detecting Pk, Pm, and Po monoinfections.

Results

Among 40 studies included in the review, 3 reported on Pk, 8 on Pm, 5 on Po, 1 on Pk and Pm, and 23 on Pm and Po infections. In the meta-analysis, estimates of sensitivities of RDTs in detecting Pk infections ranged 2%-48%. Test performances for Pm and Po infections were less accurate and highly heterogeneous, mainly because of the small number of samples tested.

Conclusions

Limited data available suggest that malaria RDTs show suboptimal performance for detecting Pk, Pm, and Po infections. New improved RDTs and appropriately designed cross-sectional studies to demonstrate the usefulness of RDTs in the detection of neglected Plasmodium species are urgently needed.

Indigenous Plasmodium malariae Infection in an Endemic Population at the Thai-Myanmar Border

Plasmodium malariae is a neglected malaria parasite. It has wide geographic distribution and, although often associated with mild malaria, is linked to a high burden of anemia and nephrotic syndromes. Here, we report a cohort study conducted in the Kanchanaburi Province of Thailand during May 2013-June 2014 in which P. malariae infection was detected. Of the 812 study participants, two were found to be infected with P. malariae. One had an infection that led to acute malaria, but the other was positive for P. malariae at multiple visits during the study and apparently had chronic asymptomatic infection. Such persistent infection may explain how P. malariae has been able to thrive at very low prevalence and represents a challenge for malaria elimination.

Development of an agent-based model to assess the impact of substandard and falsified anti-malarials: Uganda case study

BACKGROUND

Global efforts to address the burden of malaria have stagnated in recent years with malaria cases beginning to rise. Substandard and falsified anti-malarial treatments contribute to this stagnation. Poor quality anti-malarials directly affect health outcomes by increasing malaria morbidity and mortality, as well as threaten the effectiveness of treatment by contributing to artemisinin resistance. Research to assess the scope and impact of poor quality anti-malarials is essential to raise awareness and allocate resources to improve the quality of treatment. A probabilistic agent-based model was developed to provide country-specific estimates of the health and economic impact of poor quality anti-malarials on paediatric malaria. This paper presents the methodology and case study of the Substandard and Falsified Antimalarial Research Impact (SAFARI) model developed and applied to Uganda.

RESULTS

The total annual economic impact of malaria in Ugandan children under age five was estimated at US$614 million. Among children who sought medical care, the total economic impact was estimated at $403 million, including $57.7 million in direct costs. Substandard and falsified anti-malarials were a significant contributor to this annual burden, accounting for $31 million (8% of care-seeking children) in total economic impact involving $5.2 million in direct costs. Further, 9% of malaria deaths relating to cases seeking treatment were attributable to poor quality anti-malarials. In the event of widespread artemisinin resistance in Uganda, we simulated a 12% yearly increase in costs associated with paediatric malaria cases that sought care, inflicting $48.5 million in additional economic impact annually.

CONCLUSIONS

Improving the quality of treatment is essential to combat the burden of malaria and prevent the development of drug resistance. The SAFARI model provides country-specific estimates of the health and economic impact of substandard and falsified anti-malarials to inform governments, policy makers, donors and the malaria community about the threat posed by poor quality medicines. The model findings are useful to illustrate the significance of the issue and inform policy and interventions to improve medicinal quality.

Comparison of three diagnostic methods (microscopy, RDT, and PCR) for the detection of malaria parasites in representative samples from Equatorial Guinea

Background

Malaria in Equatorial Guinea remains a major public health problem. The country is a holo-endemic area with a year-round transmission pattern. In 2016, the prevalence of malaria was 12.09% and malaria caused 15% of deaths among children under 5 years. In the Continental Region, 95.2% of malaria infections were Plasmodium falciparum, 9.5% Plasmodium vivax, and eight cases mixed infection in 2011. The main strategy for malaria control is quick and accurate diagnosis followed by effective treatment. Early and accurate diagnosis of malaria is essential for both effective disease management and malaria surveillance. The quality of malaria diagnosis is important in all settings, as misdiagnosis can result in significant morbidity and mortality. Microscopy and RDTs are the primary choices for diagnosing malaria in the field. However, false-negative results may delay treatment and increase the number of persons capable of infecting mosquitoes in the community. The present study analysed the performance of microscopy and RDTs, the two main techniques used in Equatorial Guinea for the diagnosis of malaria, compared to semi-nested multiplex PCR (SnM-PCR).

Results

A total of 1724 samples tested by microscopy, RDT, and SnM-PCR were analysed. Among the negative samples detected by microscopy, 335 (19.4%) were false negatives. On the other hand, the negative samples detected by RDT, 128 (13.3%) were false negatives based on PCR. This finding is important, especially since it is a group of patients who did not receive antimalarial treatment.

Conclusions

Owing to the high number of false negatives in microscopy, it is necessary to reinforce training in microscopy, the “Gold Standard” in endemic areas. A network of reference centres could potentially support ongoing diagnostic and control efforts made by malaria control programmes in the long term, as the National Centre of Tropical Medicine currently supports the National Programme against Malaria of Equatorial Guinea to perform all of the molecular studies necessary for disease control. Taking into account the results obtained with the RDTs, an exhaustive study of the deletion of the hrp2 gene must be done in EG to help choose the correct RDT for this area.

Emergence of Nonfalciparum Plasmodium Infection Despite Regular Artemisinin Combination Therapy in an 18-Month Longitudinal Study of Ugandan Children and Their Mothers

As part of a longitudinal cohort investigation of intestinal schistosomiasis and malaria in Ugandan children and their mothers on the shorelines of Lakes Victoria and Albert, we documented risk factors and morbidity associated with nonfalciparum Plasmodium infections and the longitudinal dynamics of Plasmodium species in children. Host age, household location, and Plasmodium falciparum infection were strongly associated with nonfalciparum Plasmodium infections, and Plasmodium malariae infection was associated with splenomegaly. Despite regular artemisinin combination therapy treatment, there was a 3-fold rise in P. malariae prevalence, which was not accountable for by increasing age of the child. Worryingly, our findings reveal the consistent emergence of nonfalciparum infections in children, highlighting the complex dynamics underlying multispecies infections here. Given the growing body of evidence that nonfalciparum malaria infections cause significant morbidity, we encourage better surveillance for nonfalciparum Plasmodium infections, particularly in children, with more sensitive DNA detection methods and improved field-based diagnostics.

Submicroscopic malaria cases play role in local transmission in Trenggalek district, East Java Province, Indonesia

Background

Trenggalek district is a hypoendemic malaria area with mainly imported cases brought by migrant workers from islands outside Java. During malaria surveillance in 2015, no malaria cases were found microscopically, but some cases were positive by PCR. Therefore, a study was conducted to prove that local malaria transmission still occur.

Methods

The adult villagers were invited to the house of the head of this village to be screened for malaria using aseptic venipuncture of 1 mL blood upon informed consent. Thin and thick blood films as well as blood spots on filter paper were made for each subject. The blood films were stained with Giemsa and the blood spots were used to extract DNA for polymerase chain reaction (PCR) amplification to determine the malaria infection. In addition, the history of malaria infection and travel to malaria endemic areas were recorded. Entomologic survey to detect the existence of anopheline vector was also conducted.

Results

Of the total 64 subjects that participated in the survey, no malaria parasites were found through microscopic examination of the blood films. The PCR analysis found six positive cases (two Plasmodium falciparum, one Plasmodium vivax and two mixed infection of both species), and two of them had no history of malaria and have never travelled to malaria endemic area. Entomologic survey using human bait trap detected the existence of Anopheles indefinitus that was found to be positive for P. vivax by PCR.

Conclusions

The results indicated that although we did not find any microscopically slide positive cases, six PCR positive subjects were found. The fact that 2 of the 6 malaria positive subjects have never travelled to malaria endemic area together with the existence of the vector confirm the occurence of local transmission of malaria in the area.

Detection of Plasmodium Species by High-Resolution Melt Analysis of DNA from Blood Smears Acquired in Southwestern Uganda

Microscopic diagnosis of malaria using Giemsa-stained blood smears is the standard of care in resource-limited settings. These smears represent a potential source of DNA for PCR testing to confirm Plasmodium infections or for epidemiological studies of archived samples. Therefore, we assessed the use of DNA extracts from stained blood smears for the detection of Plasmodium species using real-time PCR. We extracted DNA from archived blood smears and corresponding red blood cell pellets collected from asymptomatic children in southwestern Uganda in 2010. We then performed real-time PCR followed by high-resolution melting (HRM) to identify Plasmodium species, and we compared our results to those of microscopy. We analyzed a total of 367 blood smears and corresponding red blood cell pellets, including 185 smears (50.4%) that were positive by microscopy. Compared to microscopy, PCR-HRM analysis of smear DNA had a sensitivity of 93.0% (95% confidence interval [CI], 88.2 to 96.2%) and a specificity of 96.7% (95% CI, 93.0 to 98.8%), and PCR-HRM analysis of pellet DNA had a sensitivity of 100.0% (95% CI, 98.0 to 100.0%) and a specificity of 94.0% (95% CI, 89.4 to 96.9%). Identification of positive PCR-HRM results to the species level revealed Plasmodium falciparum (92.0%), Plasmodium ovale (5.6%), and Plasmodium malariae (2.4%). PCR-HRM analysis of DNA extracts from Giemsa-stained thick blood smears or corresponding blood pellets had high sensitivity and specificity for malaria diagnosis, compared to microscopy. Therefore, blood smears can provide an adequate source of DNA for confirmation of Plasmodium species infections and can be used for retrospective genetic studies.

Performance of Loop-Mediated Isothermal Amplification for the Identification of Submicroscopic Plasmodium falciparum Infection in Uganda

Accurately identifying and targeting the human reservoir of malaria parasitemia is critical for malaria control, and requires a reliable and sensitive diagnostic method. Loop-mediated isothermal amplification (LAMP) is increasingly used to diagnose submicroscopic parasitemia. Although most published studies report the sensitivity of LAMP compared with nested polymerase chain reaction (PCR) as ≥ 80%, they have failed to use a consistent, sensitive diagnostic as a comparator. We used cross-sectional samples from children and adults in Tororo, Uganda, a region with high but declining transmission due to indoor residual spraying, to characterize the sensitivity and specificity of pan-Plasmodium LAMP for detecting submicroscopic infections. We compared LAMP results targeting a mitochondrial DNA sequence conserved in all Plasmodium species, performed on DNA extracted from dried blood spots, to those of a gold standard quantitative PCR assay targeting the var gene acidic terminal sequence of Plasmodium falciparum (varATS qPCR), performed on DNA extracted from 200 µL of whole blood. Using LAMP and varATS qPCR increased the detection of parasitemia 2- to 5-fold, compared with microscopy. Among microscopy-negative samples, the sensitivity of LAMP was 81.5% for detecting infection ≥ 1 parasites/µL. However, low density infections were common, and LAMP failed to identify more than half of all infections diagnosed by varATS qPCR, performing with an overall sensitivity of 44.7% for detecting submicroscopic infections ≥ 0.01 parasites/µL. Thus, although the LAMP assay is more sensitive than microscopy, it missed a significant portion of the submicroscopic reservoir. These findings have important implications for malaria control, particularly in settings where low-density infections predominate.

Evaluation of the Deki Reader™, an automated RDT reader and data management device, in a household survey setting in low malaria endemic southwestern Uganda

Background

Early diagnosis of suspected malaria cases with a rapid diagnostic test (RDT) has been shown to be an effective malaria control tool used in many resource-constrained settings. However, poor quality control and quality assurance hinder the accurate reporting of malaria diagnoses. Recent use of a portable, battery operated RDT reader (Deki Reader™, Fio Corporation) has shown to have high agreement with visual inspection across diverse health centre settings, however evidence of its feasibility and usability during cross sectional surveys are limited. This study aimed to evaluate the performance of the Deki Reader™ in a cross-sectional survey of children from southwestern Uganda.

Methods

A two-stage, stratified cluster sampling survey was conducted between July and October 2014 in three districts of southwestern Uganda, with varying malaria transmission intensities. A total of 566 children aged 6–59 months were included in the analysis. Blood samples were collected and tested for malaria using: the SD Bioline Malaria Ag Pf/Pan RDT and microscopy. Results were compared between visual inspection of the RDT and by the Deki Reader™. Diagnostic performance of both methods were compared to gold-standard microscopy.

Results

The sensitivity and specificity of the Deki Reader™ was 94.1% (95% CI 69.2–99.6%) and 95.6% (95% CI 93.4–97.1%), respectively. The overall percent agreement between the Deki Reader™ and visual RDT inspection was 98.9% (95% CI 93.2–99.8), with kappa statistic of 0.92 (95% CI 0.85–0.98).

Conclusions

The findings from this study suggest that the Deki Reader™ is comparable to visual inspection and performs well in detecting microscopy-positive Plasmodium falciparum cases in a household survey setting. However, the reader’s performance was highly dependent on ensuring adequate battery life and a work environment free of dirt particles.

Examining the human infectious reservoir for Plasmodium falciparum malaria in areas of differing transmission intensity

A detailed understanding of the human infectious reservoir is essential for improving malaria transmission-reducing interventions. Here we report a multi-regional assessment of population-wide malaria transmission potential based on 1209 mosquito feeding assays in endemic areas of Burkina Faso and Kenya. Across both sites, we identified 39 infectious individuals. In high endemicity settings, infectious individuals were identifiable by research-grade microscopy (92.6%; 25/27), whilst one of three infectious individuals in the lowest endemicity setting was detected by molecular techniques alone. The percentages of infected mosquitoes in the different surveys ranged from 0.05 (4/7716) to 1.6% (121/7749), and correlate positively with transmission intensity. We also estimated exposure to malaria vectors through genetic matching of blood from 1094 wild-caught bloodfed mosquitoes with that of humans resident in the same houses. Although adults transmitted fewer parasites to mosquitoes than children, they received more mosquito bites, thus balancing their contribution to the infectious reservoir.

Plasmodium Species Infecting Children Presenting with Malaria in Uganda

Contributions of species other than Plasmodium falciparum to human malaria in sub-Saharan Africa are uncertain. We collected blood from children aged 6 months to 10 years diagnosed with malaria by Giemsa-stained blood smears (176 subjects) or histidine rich protein-2-based rapid diagnostic tests (323 subjects) in 2016; 50 samples from each of 10 sites across Uganda were studied to identify infecting species. Of 499 available samples, 474 demonstrated plasmodial infection by polymerase chain reaction amplification of 18S ribosomal RNA genes, including P. falciparum in 472, Plasmodium malariae in 22, Plasmodium ovale in 15, and Plasmodium vivax in four; 435 were pure P. falciparum, two did not contain P. falciparum, and the remainder were mixed infections including P. falciparum. The prevalence of nonfalciparum species varied geographically. Stratifying based on recent history of indoor residual spraying (IRS) of insecticides, nonfalciparum infections were seen in 27/189 (14.8%) samples from sites that received and 13/285 (4.6%) samples from sites that did not receive IRS since 2010 (P = 0.0013). Overall, 39/474 (8.2%) samples from individuals diagnosed with malaria included nonfalciparum infections. Thus, a substantial proportion of episodes of malaria in Uganda include infections with plasmodial species other than P. falciparum.

Plasmodium falciparum HRP2 ELISA for analysis of dried blood spot samples in rural Zambia

Background

Dried blood spots are commonly used for sample collection in clinical and non-clinical settings. This method is simple, and biomolecules in the samples remain stable for months at room temperature. In the field, blood samples for the study and diagnosis of malaria are often collected on dried blood spot cards, so development of a biomarker extraction and analysis method is needed.

Methods

A simple extraction procedure for the malarial biomarker Plasmodium falciparum histidine-rich protein 2 (HRP2) from dried blood spots was optimized to achieve maximum extraction efficiency. This method was used to assess the stability of HRP2 in dried blood spots. Furthermore, 328 patient samples made available from rural Zambia were analysed for HRP2 using the developed method. These samples were collected at the initial administration of artemisinin-based combination therapy and at several points following treatment.

Results

An average extraction efficiency of 70% HRP2 with a low picomolar detection limit was achieved. In specific storage conditions HRP2 was found to be stable in dried blood spots for at least 6 months. Analysis of patient samples showed the method to have a sensitivity of 94% and a specificity of 89% when compared with microscopy, and trends in HRP2 clearance after treatment were observed.

Conclusions

The dried blood spot ELISA for HRP2 was found to be sensitive, specific and accurate. The method was effectively used to assess biomarker clearance characteristics in patient samples, which prove it to be ideal for gaining further insight into the disease and epidemiological applications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1996-4) contains supplementary material, which is available to authorized users.

Asymptomatic Plasmodium malariae infections in children from suburban areas of Yaoundé, Cameroon

The gold standard for malaria diagnosis is the microscopic examination of Giemsa stained thick blood smears though microscopy mostly may not detect the presence of Plasmodium species infections in asymptomatic samples. In the reported study, we used two diagnostic methods viz. the conventional microscopic examination and polymerase chain reaction (PCR) assay to analyse the asymptomatic malaria samples. PCR assay amplifying 18S small-subunit ribosomal RNA (SSU rRNA) gene of Plasmodium in 122 samples confirmed 68% of isolates as asymptomatic P. falciparum infections; with 87.9% mono-infections. We observed that the P. malariae positive samples were not diagnosed in microscopic examination of the blood smears but the PCR based diagnostic method revealed the presence of 12% P. malariae infections in asymptomatic samples from Yaoundé region of Cameroon where no official cases of P. malariae have been reported for over a decade. The sequence analysis further confirmed the presence of 12% P. malariae in malaria positive samples with three base pair deletions and five substitutions in the SSU rRNA gene.

Screening for Glucose-6-Phosphate Dehydrogenase Deficiency Using Three Detection Methods: A Cross-Sectional Survey in Southwestern Uganda

Despite the potential benefit of primaquine in reducing Plasmodium falciparum transmission and radical cure of Plasmodium vivax and Plasmodium ovale infections, concerns over risk of hemolytic toxicity in individuals with glucose-6-phosphate dehydrogenase deficiency (G6PDd) have hampered its deployment. A cross-sectional survey was conducted in 2014 to assess the G6PDd prevalence among 631 children between 6 and 59 months of age in southwestern Uganda, an area where primaquine may be a promising control measure. G6PDd prevalence was determined using three detection methods: a quantitative G6PD enzyme activity assay (Trinity Biotech^® G-6-PDH kit), a qualitative point-of-care test (CareStart^™ G6PD rapid diagnostic test [RDT]), and molecular detection of the G6PD A- G202A allele. Qualitative tests were compared with the gold standard quantitative assay. G6PDd prevalence was higher by RDT (8.6%) than by quantitative assay (6.8%), using a < 60% activity threshold. The RDT performed optimally at a < 60% threshold and demonstrated high sensitivity (≥ 90%) and negative predictive values (100%) across three activity thresholds (below 60%, 30%, and 40%). G202A allele frequency was 6.4%, 7.9%, and 6.8% among females, males, and overall, respectively. Notably, over half of the G202A homo-/hemizygous children expressed ≥ 60% enzyme activity. Overall, the CareStart^™ G6PD RDT appears to be a viable screening test to accurately identify individuals with enzyme activities below 60%. The low prevalence of G6PDd across all three diagnostic modalities and absence of severe deficiency in our study suggests that there is little barrier to the use of single-dose primaquine in this region.