Co-infection of the four major Plasmodium species: Effects on densities and gametocyte carriage

Malaria Species Positivity Rates Among Symptomatic Individuals Across Regions of Differing Transmission Intensities in Mainland Tanzania

BACKGROUND

Recent data indicate that non-Plasmodium falciparum species may be more prevalent than thought in sub-Saharan Africa. Although Plasmodium malariae, Plasmodium ovale spp., and Plasmodium vivax are less severe than P. falciparum, treatment and control are more challenging, and their geographic distributions are not well characterized.

METHODS

We randomly selected 3284 of 12 845 samples collected from cross-sectional surveys in 100 health facilities across 10 regions of Mainland Tanzania and performed quantitative real-time PCR to determine presence and parasitemia of each malaria species.

RESULTS

P. falciparum was most prevalent, but P. malariae and P. ovale were found in all but 1 region, with high levels (>5%) of P. ovale in 7 regions. The highest P. malariae positivity rate was 4.5% in Mara and 8 regions had positivity rates ≥1%. We only detected 3 P. vivax infections, all in Kilimanjaro. While most nonfalciparum malaria-positive samples were coinfected with P. falciparum, 23.6% (n = 13 of 55) of P. malariae and 14.7% (n = 24 of 163) of P. ovale spp. were monoinfections.

CONCLUSIONS

P. falciparum remains by far the largest threat, but our data indicate that malaria elimination efforts in Tanzania will require increased surveillance and improved understanding of the biology of nonfalciparum species.

Identification of conserved cross-species B-cell linear epitopes in human malaria: a subtractive proteomics and immuno-informatics approach targeting merozoite stage proteins

Human malaria, caused by five Plasmodium species (P. falciparum, P. vivax, P. malariae, P. ovale, and P. knowlesi), remains a significant global health burden. While most interventions target P. falciparum, the species associated with high mortality rates and severe clinical symptoms, non-falciparum species exhibit different transmission dynamics, remain hugely neglected, and pose a significant challenge to malaria elimination efforts. Recent studies have reported the presence of antigens associated with cross-protective immunity, which can potentially disrupt the transmission of various Plasmodium species. With the sequencing of the Plasmodium genome and the development of immunoinformatic tools, in this study, we sought to exploit the evolutionary history of Plasmodium species to identify conserved cross-species B-cell linear epitopes in merozoite proteins. We retrieved Plasmodium proteomes associated with human malaria and applied a subtractive proteomics approach focusing on merozoite stage proteins. Bepipred 2.0 and Epidope were used to predict B-cell linear epitopes using P. falciparum as the reference species. The predictions were further compared against human and non-falciparum databases and their antigenicity, toxicity, and allergenicity assessed. Subsequently, epitope conservation was carried out using locally sequenced P. falciparum isolates from a malaria-endemic region in western Kenya (n=27) and Kenyan isolates from MalariaGEN version 6 (n=131). Finally, physiochemical characteristics and tertiary structure of the B-cell linear epitopes were determined. The analysis revealed eight epitopes that showed high similarity (70-100%) between falciparum and non-falciparum species. These epitopes were highly conserved when assessed across local isolates and those from the MalariaGEN database and showed desirable physiochemical properties. Our results show the presence of conserved cross-species B-cell linear epitopes that could aid in targeting multiple Plasmodium species. Nevertheless, validating their efficacy in-vitro and in-vivo experimentally is essential.

Is qPCR always the most sensitive method for malaria diagnostic quality surveillance?

In many studies to evaluate the quality of malaria diagnosis, microscopy or rapid diagnostic tests (RDT) are compared to PCR. Depending on the method for sample collection and storage (whole blood or dried blood spot), volume of blood used for extraction, volume of DNA used as PCR template, and choice of PCR target (single vs. multi-copy gene), the limit of detection (LOD) of PCR might not exceed the LOD of expert microscopy or RDT. One should not assume that PCR always detects the highest number of infections.

A novel duplex qualitative real-time PCR assay for the detection and differentiation of Plasmodium ovale curtisi and Plasmodium ovale wallikeri malaria

Background

P. ovale spp. infections are endemic across multiple African countries and are caused by two distinct non-recombining species, P. ovale curtisi (Poc) and P. ovale wallikeri (Pow). These species are thought to differ in clinical symptomatology and latency, but existing diagnostic assays have limited ability to detect and distinguish them. In this study, we developed a new duplex assay for the detection and differentiation of Poc and Pow that can be used to improve our understanding of these parasites.

Methods

Repetitive sequence motifs were identified in available Poc and Pow genomes and used for assay development and validation. We evaluated the analytical sensitivity and specificity of the best-performing assay using a panel of samples from Tanzania and the Democratic Republic of the Congo (DRC), then validated its performance using 55 P. ovale spp. samples and 40 non-ovale Plasmodium samples from the DRC. Poc and Pow prevalence among symptomatic individuals sampled across three provinces of the DRC were estimated.

Results

The best-performing Poc and Pow targets had 9 and 8 copies within the reference genomes, respectively. Our duplex assay had 100% specificity and 95% confidence lower limits of detection of 4.2 and 41.2 parasite genome equivalents/μl for Poc and Pow, respectively. Species was determined in 80% of all P. ovale spp.-positive field samples and 100% of those with >10 parasites/μl. Most P. ovale spp. field samples from the DRC were found to be Poc infections.

Conclusions

We identified promising multi-copy targets for molecular detection and differentiation of Poc and Pow and used them to develop a new duplex real-time PCR assay that performed well when applied to diverse field samples. Though low-density Pow infections are not reliably detected, the assay is highly specific and can be used for high-throughput studies of P. ovale spp. epidemiology among symptomatic cases in malaria-endemic countries like the DRC.

Sensitive Detection of Asymptomatic and Symptomatic Malaria with Seven Novel Parasite-Specific LAMP Assays and Translation for Use at Point-of-Care

Human malaria is a life-threatening parasitic disease with high impact in the sub-Saharan Africa region, where 95% of global cases occurred in 2021. While most malaria diagnostic tools are focused on Plasmodium falciparum, there is a current lack of testing non-P. falciparum cases, which may be underreported and, if undiagnosed or untreated, may lead to severe consequences. In this work, seven species-specific loop-mediated isothermal amplification (LAMP) assays were designed and evaluated against TaqMan quantitative PCR (qPCR), microscopy, and enzyme-linked immunosorbent assays (ELISAs). Their clinical performance was assessed with a cohort of 164 samples of symptomatic and asymptomatic patients from Ghana. All asymptomatic samples with a parasite load above 80 genomic DNA (gDNA) copies per μL of extracted sample were detected with the Plasmodium falciparum LAMP assay, reporting 95.6% (95% confidence interval [95% CI] of 89.9 to 98.5) sensitivity and 100% (95% CI of 87.2 to 100) specificity. This assay showed higher sensitivity than microscopy and ELISA, which were 52.7% (95% CI of 39.7 to 67%) and 67.3% (95% CI of 53.3 to 79.3%), respectively. Nine samples were positive for P. malariae, indicating coinfections with P. falciparum, which represented 5.5% of the tested population. No samples were detected as positive for P. vivax, P. ovale, P. knowlesi, or P. cynomolgi by any method. Furthermore, translation to the point-of-care was demonstrated with a subcohort of 18 samples tested locally in Ghana using our handheld lab-on-chip platform, Lacewing, showing comparable results to a conventional fluorescence-based instrument. The developed molecular diagnostic test could detect asymptomatic malaria cases, including submicroscopic parasitemia, and it has the potential to be used for point-of-care applications. IMPORTANCE The spread of Plasmodium falciparum parasites with Pfhrp2/3 gene deletions presents a major threat to reliable point-of-care diagnosis with current rapid diagnostic tests (RDTs). Novel molecular diagnostics based on nucleic acid amplification are needed to address this liability. In this work, we overcome this challenge by developing sensitive tools for the detection of Plasmodium falciparum and non-P. falciparum species. Furthermore, we evaluate these tools with a cohort of symptomatic and asymptomatic malaria patients and test a subcohort locally in Ghana. The findings of this work could lead to the implementation of DNA-based diagnostics to fight against the spread of malaria and provide reliable, sensitive, and specific diagnostics at the point of care.

Impact of the COVID-19 Pandemic on Malaria Control in Africa: A Preliminary Analysis

Malaria remains a significant public health concern in Africa, and the emerging coronavirus disease 2019 (COVID-19) pandemic may have negatively impacted malaria control. Here, we conducted a descriptive epidemiological analysis of malaria globally, and preliminarily explored the impact of COVID-19 on the malaria elimination program in regions of Africa (AFR). The present analysis found that there was a vast heterogeneity of incidence of deaths caused by malaria globally in different continents, and the highest malaria burden was observed in AFR. In 2020, there was an obviously increasing trend in the malaria epidemic in AFR, while the other four continents exhibited stable and declining patterns. Historically, malaria has been largely concentrated in high-malaria-burden regions, such as West Africa, and there has been an obvious increasing trend in Nigeria. These data suggest that dynamic changes in the malaria epidemic situation worldwide have primarily originated from AFR, and West Africa has played an important role in the global malaria increase in recent years. Under the coercion of COVID-19, multiple factors have co-driven the increase in malaria in AFR, including insufficient financial investments, a high native malaria burden, weak surveillance systems, limited medical resources, and low socioeconomic development levels. In addition, the shift of medical resources (e.g., health workers and personal protective equipment (PPE), the manufacturing of diagnostic reagents, and drugs) from malaria control to emergency COVID-19 response in the pandemic's early stage caused disruptions, reductions, and delays in pillar malaria control measures, leading to a significant negative impact on malaria control. In particular, a funding shortfall at both the international and domestic levels led to a "significant threat," resulting in vast gaps in access to proven malaria control tools. Although there has been a declining trend in malaria control over time due to COVID-19, the effect still cannot be ignored. Hence, we recommend the implementation of medical and technical resource assistance as a priority strategy to support Africa (West Africa) in order to curb further transmission.