Plasmodium malariae: the persisting mysteries of a persistent parasite

Metagenomic analysis reveals extreme complexity of Plasmodium spp. infections in high transmission in West Africa

Mixed-species, mixed-strain Plasmodia infections are known to occur in humans in malaria endemic areas. To date, the true extent of this complexity has not been explored in high-burden countries of sub-Saharan Africa. Here we take a metagenomic lens to infections obtained by sampling variable blood volumes from residents living in high, seasonal transmission in northern Ghana. We identified significantly higher prevalence of Plasmodium spp. and inter-/intra-species complexity in larger blood volumes. Overall, malaria infections displayed high levels of metagenomic complexity comprising single-, double-, and triple-species infections with varying levels of complexity for P. falciparum, P. malariae, P. ovale curtisi, and P. ovale wallikeri. We present evidence of individuals with greater susceptibility to highly-complex infections that cannot be explained by age or location. The implications of these findings to malaria epidemiology and control are illustrated by a geographic scaling exercise to district and region levels in Ghana.

Prevalence and epidemiological characteristics of asymptomatic malaria in Sucre, Venezuela: a 2022 cross-sectional study

BACKGROUND

Despite a significant reduction in malaria cases in America, Venezuela has experienced a substantial increase between 2000 and 2019. Asymptomatic malaria, prevalent in both low- and high-endemic regions, poses a challenge due to the absence of clinical manifestations and often low parasitaemia. This study aims to determine the current prevalence of asymptomatic malaria in four rural communities of Sucre, the third most endemic state in the country.

METHODS

A community-based cross-sectional study was conducted from October to December 2022 (high seasonality period). Individuals were interviewed in their households and assessed for malaria using rapid diagnostic tests (RDTs), thick and thin blood smear microscopy, and polymerase chain reaction (PCR). Asymptomatic individuals with PCR positive (PCR+) for Plasmodium were classified as cases, while PCR negative individuals were classified as controls. Descriptive statistics were used to analyse the data. The normality of numerical variables was assessed with the Kolmogorov-Smirnov test. Based on this assessment, Student's t-test was applied to normally distributed variables and Mann-Whitney U-test to non-normally distributed ones. For categorical variables, Pearson's chi-square test was used when less than 25.0% of cells had an expected frequency below five; otherwise, Fisher's exact test was employed.

RESULTS

The study involved 351 individuals, mostly women (54.7%), of mixed (non-indigenous) race (61.3%), with primary (6 years) education (40.7%). The most common occupations were students (30.5%), housekeepers (27.6%), and farmers (16.5%). Over half (54.4%) had lived at their current address for over 10 years. The prevalence of asymptomatic malaria by RDTs and microscopy was 0.3% (n = 1/351) as determined. However, PCR detected a higher prevalence of 24.8% (87 positive cases, 95.0% CI = 20.5-29.5), primarily caused by P. vivax (73.6%). The highest prevalences were observed in individuals aged over 15 years (27.1%, 95.0% CI = 21.6-33.1), males (28.3%, 95.0% CI = 21.7-35.6), those with a college (14 years) education (33.3%, 95.0% CI = 17.2-53.2), and educators (41.7%, 95.0% CI = 18-68.8). The rural community with the highest prevalence was Chacopata (30.6%, 95.0% CI = 17.4-46.7), followed by El Paujil (28.6%, 95.0% CI = 21.9-36.1), Yaguaraparo (23.2%, 95.0% CI = 15.1-33.1), and Cristóbal Colón (16.5%, 95.0% CI = 9.6-25.8). Two-thirds (66.7%) reported a malaria history, predominantly caused by P. vivax (70.5%), with a median of 3 previous episodes. At least one-third (35.5%) had non-adherence to treatment during their most recent malarial episode. No statistically significant differences were observed between sociodemographic characteristics and malaria history of individuals with asymptomatic malaria (PCR+) and controls.

CONCLUSION

RDTs and microscopy only managed to diagnose less than 1.0% of asymptomatic malaria cases. Active surveillance systems with high sensitivity such as PCR may provide accurate estimates of asymptomatic malaria prevalence needed for opportune diagnosis and treatment.

Malian field isolates provide insight into Plasmodium malariae intra-erythrocytic development and invasion

Plasmodium malariae is the third most prevalent human malaria parasite species and contributes significantly to morbidity. Nevertheless, our comprehension of this parasite's biology remains limited, primarily due to its frequent co-infections with other species and the lack of a continuous in vitro culture system. To effectively combat and eliminate this overlooked parasite, it is imperative to acquire a better understanding of this species. In this study, we embarked on an investigation of P. malariae, including exploring its clinical disease characteristics, molecular aspects of red blood cell (RBC) invasion, and host-cell preferences. We conducted our research using parasites collected from infected individuals in Mali. Our findings revealed anaemia in most of P. malariae infected participants presented, in both symptomatic and asymptomatic cases. Regarding RBC invasion, quantified by an adapted flow cytometry based method, our study indicated that none of the seven antibodies tested, against receptors known for their role in P. falciparum invasion, had any impact on the ability of P. malariae to penetrate the host cells. However, when RBCs were pre-treated with various enzymes (neuraminidase, trypsin, and chymotrypsin), we observed a significant reduction in P. malariae invasion, albeit not a complete blockade. Furthermore, in a subset of P. malariae samples, we observed the parasite's capability to invade reticulocytes. These results suggest that P. malariae employs alternative pathways to enter RBCs of different maturities, which may differ from those used by P. falciparum.

Exploring potential Plasmodium kinase inhibitors: a combined docking, MD and QSAR studies

Malaria is a disease caused mostly by Plasmodium falciparum, affects millions of people each year. The kinases are validated targets for malaria infection. In this study, we investigate for real and hypothetical compounds that can inhibit cyclic guanosine monophosphate (CGMP)-dependent protein kinase using molecular docking via combined similarity analysis, molecular dynamics simulations, quantitative structure activity relationship (QSAR). Using Tanimoto similarity scores, ∼8.4 million compounds were screened. Compounds that have at least 70% similarity are used in further analysis. These compounds are assessed by means of docking, MMBPSA, MMGBSA and ANI_LIE. Based on consensus of different free energy methods and docking we revealed two potential inhibitors that can be useful for treatment of malaria. Apart from screening of real compounds, we have also selected the 10 most plausible hypothetical compounds by performing QSAR. By QSAR proposed pharmacophores, we generated over 247 hypothetical compounds and among them 19 molecules with lower QSAR predicted IC50 values and high docking scores were selected for further analysis. We selected the top 10 inhibitor candidates and performed MD simulations for free energy calculations like the protocol applied for real compounds. According to the free energy calculations, we suggest 2 real (C34H29F5N8O4S and C30H27F2N7O2S2, PubChem IDs: 140564801 and 89035196, respectively) and 2 hypothetical (C23H27FN6O2S, MOL3 and C23H25FN6O2S, MOL4) compounds that can be effective inhibitors against the protein kinase of Plasmodium falciparum.Communicated by Ramaswamy H. Sarma.

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.

Epidemiological characteristics of Plasmodium malariae malaria in China: a malaria that should not be neglected post elimination

BACKGROUND

Plasmodium malariae was always neglected compared with P. falciparum and P. vivax. In the present study, we aimed to describe the epidemiology of reported cases infected with P. malariae in the past decade to raise awareness of the potential threat of this malaria parasite in China.

METHODS

Individual data of malaria cases infected with P. malariae reported in China in the past decade were collected via the China Information System for Disease Control and Prevention and Parasitic Diseases Information Reporting Management System, to explore their epidemiological characteristics. Pearson Chi-square tests or Fisher's Exact Test was used in the statistical analysis.

RESULTS

From 2013 to 2022, a total of 581 P. malariae cases were reported in China, and mainly concentrated in 20-59 years old group (P < 0.001), and there was no significant trend in the number of cases reported per month. Moreover, four kinds of P. malariae cases were classified, including 567 imported cases from 41 countries in 8 regions and distributed in 27 provinces (autonomous regions, municipalities) in China, six indigenous cases in a small outbreak in Hainan, seven recurrent cases in Guangdong and Shanghai, and one induced case in Shanghai, respectively. In addition, only 379 cases (65.2%) were diagnosed as malaria on the first visit (P < 0.001), and 413 cases (71.1%) were further confirmed as P. malariae cases (P = 0.002). Meanwhile, most cases sought healthcare first in the health facilities at the county and prefectural levels, but only 76.7% (161/210) and 73.7% (146/198) cases were diagnosed as malaria, and the accuracy of confirmed diagnosis as malaria cases infected with P. malariae was only 77.2% (156/202) and 69.9% (167/239) in these health facilities respectively.

CONCLUSIONS

Even though malaria cases infected with P. malariae didn't account for a high proportion of reported malaria cases nationwide, the threat posed by widely distributed imported cases, a small number of indigenous cases, recurrent cases and induced case cannot be ignored in China. Therefore, it is necessary to raise awareness and improve the surveillance and response to the non-falciparum species such as P. malariae, and prevent the reestablishment of malaria transmission after elimination.

Insight into molecular diagnosis for antimalarial drug resistance of Plasmodium falciparum parasites: A review

Malaria is an infectious disease transmitted by the female Anopheles mosquito and poses a severe threat to human health. At present, antimalarial drugs are the primary treatment for malaria. The widespread use of artemisinin-based combination therapies (ACTs) has dramatically reduced the number of malaria-related deaths; however, the emergence of resistance has the potential to reverse this progress. Accurate and timely diagnosis of drug-resistant strains of Plasmodium parasites via detecting molecular markers (such as Pfnhe1, Pfmrp, Pfcrt, Pfmdr1, Pfdhps, Pfdhfr, and Pfk13) is essential for malaria control and elimination. Here, we review the current techniques which commonly used for molecular diagnosis of antimalarial resistance in P. falciparum and discuss their sensitivities and specificities for different drug resistance-associated molecular markers, with the aim of providing insights into possible directions for future precise point-of-care testing (POCT) of antimalarial drug resistance of malaria parasites.