Plasmodium falciparum clearance time in Malawian children with cerebral malaria: a retrospective cohort study

Exploring the dichotomy: Shotgun metagenomics reveals diversity of beneficial and pathogenic protist community in arid wetlands of northeastern South Africa

Arid regions harbor seasonal and permanent wetlands, as biodiversity hotspots crucial for ecosystem services despite harsh conditions. These wetlands, typically dependent on episodic intense rainfall, are understudied compared to their humid counterparts. While the diversity of plants and animals in these wetlands is well-known, the microbial communities remain largely unexplored. To address this knowledge gap, we employed metagenome sequencing technologies to profile protist communities, including pathogenic protozoa, and their associated functional pathways, in sediment of permanent and seasonal arid freshwater wetlands across northern South Africa. Results revealed a core community of protists dominated by phylum Apicomplexa (66.73 %), Euglenazoa (19.03 %), Bacillariophyta (5.44 %), Metamonada (4.65 %), Cryptophyta (1.90 %), and Amoebazoa (1.21 %). Seasonal wetlands showed significantly higher protist diversity compared to permanent wetlands (Shannon index, p = 0.019; Chao1, p = 0.0095). A high abundance and diversity of human and zoonotic pathogenic protists (87.67 %) was observed, with lower levels of photoautotrophs (6.69 %) and limited diversity of phagotrophs (5.64 %). Key photoautotrophs identified included diatoms (Thalassiosiraceae and Phaeodactylaceae) and cryptophytes (genus Hemiselmis and Cryptophyta), with consumers/phagotrophs exhibited a correlation with the bacterial community abundance (r2 = 0.218, p < 0.001). Pathogenic protozoans identified, include malaria-causing Plasmodium, kinetoplastids (genus Besnoita, Theilleria, Neospora, Toxoplasma, Encephalitozoon, and Babesia) and waterborne protozoans of public health importance (such as Cryptosporidium parvum and Giardia lamblia). Furthermore, the enrichment of pathogenesis-associated pathways (amino acid biosynthesis, peptidoglycan maturation, heme biosynthesis and degradation, and the Calvin-Benson-Bassham cycle), along with virulence gene families identified, highlighted these wetlands as potential reservoirs for infectious diseases. Our results unveil a baseline protist taxonomic and functional composition within arid wetlands, including beneficial and pathogenic protozoa. The close proximity of these wetlands to human activity raises concern for local and transboundary spread of these pathogens. Thus, continued monitoring is vital for disease control and preserving these unique ecosystems.

Estimated distribution of malaria cases among children in sub-Saharan Africa by specified age categories using data from the Global Burden of Diseases 2019

BACKGROUND

Children in sub-Saharan Africa (SSA) remain the most vulnerable to malaria and malaria mortality. This study estimated the disease burden and distribution of Plasmodium falciparum malaria among children with age categories (0 to < 2 years, 2 to < 6 years, 6 to < 12 years, ≥ 12 years) in SSA.

METHODS

Data on the number of cases and incidence rates of P. falciparum malaria by age group from the Institute of Health Metrics and Evaluation (GBD 2019) for 11 countries in SSA was employed in this study. The best-fitting distribution of P. falciparum malaria cases by prespecified age categories was derived using a combination of a Log-normal and Weibull distribution.

RESULTS

Plasmodium falciparum malaria was 15.4% for ages 0 to < 2 years, 30.5% for 2 to < 6 years, 17.6% for 6 to < 12 years, and 36.5% for ≥ 12 years based on data from countries in SSA. The results have important implications for the current drive by the FDA and EMA to ensure the representativeness of real-world populations in clinical trials evaluating the safety and efficacy of medication exposure.

CONCLUSIONS

The theoretical distributions of P. falciparum malaria will help guide researchers in ensuring that children are appropriately represented in clinical trials and other interventions aiming to address the current burden of malaria in SSA.

Differential Effects of Antimalarial Drugs on Parasite Clearance Rates Are Reflected by Plasmodium falciparum Ring Ratio

Background

The location of Plasmodium falciparum within the body is determined by the life cycle of the parasite; young rings are in the peripheral blood, whereas mature parasites are sequestered in deep tissues. We can calculate a "ring ratio," the proportion of parasites in the periphery to the total number of parasites in the body. Artesunate acts on all parasite life stages, whereas quinine is effective only on sequestered parasites. Children with cerebral malaria (CM) treated with artesunate clear parasites faster than those treated with quinine. In this study, we established the relationship between ring ratio and parasite clearance rate and used the ring ratio to determine if the benefit derived from artesunate treatment could be attributed to its broader effect on life cycle stages.

Methods

Ring ratios were calculated for 400 hospitalized children with CM in Blantyre, Malawi between 2010 and 2019 (quinine: 2010-2013, artesunate: 2014-2019).

Results

In both treatment groups, parasite clearance rates were positively associated with the ring ratios, with a stronger association in the artesunate era than the quinine era. In the quinine era, an increase of 1-unit log₁₀ difference between parasitemia and plasma P falciparum histidine-rich protein 2 (a proxy for ring ratio) resulted in a 0.27-unit increase in the parasite clearance rate, whereas in the artesunate era an equal increase resulted in a 0.41-unit increase (P = .04 for the difference).

Conclusions

This analysis provides in vivo evidence supporting the hypothesis that more rapid parasite clearance rates in artesunate recipients are due to its superiority over quinine in killing ring-stage parasites.