Haematological response in experimental human Plasmodium falciparum and Plasmodium vivax malaria

Background Malaria-associated anaemia, arising from symptomatic, asymptomatic and submicroscopic infections, is a significant cause of morbidity worldwide. Induced blood stage malaria volunteer infection studies (IBSM-VIS) provide a unique opportunity to evaluate the haematological response to early Plasmodium falciparum and Plasmodium vivax infection. Methods This study was an analysis of the haemoglobin, red cell counts, and parasitaemia data from 315 participants enrolled in IBSM-VIS between 2012 and 2019, including 269 participants inoculated with the 3D7 strain of P. falciparum (Pf3D7), 15 with an artemisinin-resistant P. falciparum strain (PfK13) and 46 with P. vivax. Factors associated with the fractional fall in haemoglobin (Hb-FF) were evaluated, and the malaria-attributable erythrocyte loss after accounting for phlebotomy-related losses was estimated. The relative contribution of parasitized erythrocytes to the malaria-attributable erythrocyte loss was also estimated. Results The median peak parasitaemia prior to treatment was 10,277 parasites/ml (IQR 3566–27,815), 71,427 parasites/ml [IQR 33,236–180,213], and 34,840 parasites/ml (IQR 13,302–77,064) in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. The median Hb-FF was 10.3% (IQR 7.8–13.3), 14.8% (IQR 11.8–15.9) and 11.7% (IQR 8.9–14.5) in those inoculated with Pf3D7, PfK13 and P. vivax, respectively, with the haemoglobin nadir occurring a median 12 (IQR 5–21), 15 (IQR 7–22), and 8 (IQR 7–15) days following inoculation. In participants inoculated with P. falciparum, recrudescence was associated with a greater Hb-FF, while in those with P. vivax, the Hb-FF was associated with a higher pre-treatment parasitaemia and later day of anti-malarial treatment. After accounting for phlebotomy-related blood losses, the estimated Hb-FF was 4.1% (IQR 3.1–5.3), 7.2% (IQR 5.8–7.8), and 4.9% (IQR 3.7–6.1) in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. Parasitized erythrocytes were estimated to account for 0.015% (IQR 0.006–0.06), 0.128% (IQR 0.068–0.616) and 0.022% (IQR 0.008–0.082) of the malaria-attributable erythrocyte loss in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. Conclusion Early experimental P. falciparum and P. vivax infection resulted in a small but significant fall in haemoglobin despite parasitaemia only just at the level of microscopic detection. Loss of parasitized erythrocytes accounted for < 0.2% of the total malaria-attributable haemoglobin loss.

Novel RNA viruses associated with avian haemosporidian parasites

Avian haemosporidian parasites can cause malaria-like symptoms in their hosts and have been implicated in the demise of some bird species. The newly described Matryoshka RNA viruses (MaRNAV1 and MaRNAV2) infect parasites that in turn infect their vertebrate hosts. MaRNAV2 was the first RNA virus discovered associated with parasites of the genus Leucocytozoon. By analyzing metatranscriptomes from the NCBI SRA database with local sequence alignment tools, we detected two novel RNA viruses; we describe them as MaRNAV3 associated with Leucocytozoon and MaRNAV4 associated with Parahaemoproteus. These had ~40-60% amino acid identity to the RNA-dependent RNA-polymerase (RdRp) of MaRNAV1 and 2, respectively. These findings lead us to hypothesize that MaRNAV_like viruses are widespread and tightly associated with the order Haemosporida since they have been described in human Plasmodium vivax, and now two genera of avian haemosporidians.

The discovery of human Plasmodium among domestic animals in West Sumba and Fakfak, Indonesia

Background: In Indonesia, malaria incidence is at a high rate despite maximum preventive efforts. Therefore, this study aims to determine the possibility of a Plasmodium reservoir among domestic animals in malaria-endemic areas. Methods: Animal blood was collected using EDTA tubes, then smeared and stained with Giemsa for Plasmodium microscopic identification. About 10 µl of blood was dropped on to a filter paper to capture Plasmodium DNA. Nested PCR was used for parasite molecular detection, while Plasmodium species were identified using the sequenced DNA. Results: A total of 208 and 62 animal blood samples were collected from Gaura village, West Sumba and Fakfak village, West Papua, Indonesia respectively. In total, 32 samples from Gaura contained P. falciparum or P. vivax, while the Plasmodium percentage in buffalo, horse, goat, and dogs were 20.7%, 14.3%, 5.8%, 16.7%, respectively. P. knowlesi was not found in any of the samples, and no other species were detected in 18 pig blood samples. Conclusion: Human Plasmodium existence among domestic animals in Indonesia partly explains the high prevalence and persistence of malaria in some endemic areas due to a reservoir host presence. Therefore, future studies need to ascertain the cause.

An Optimized Real-Time qPCR Method for the Effective Detection of Human Malaria Infections

Polymerase chain reaction, although an expensive method for the detection of human Plasmodium spp., is still considered the finest for the diagnosis of malaria. The conventional diagnostic PCR is an inexpensive process but consumes a lot of time, reagents and lacks sensitivity. On the other hand, real-time PCR assays currently being used are mostly probe-based expensive methods and sometimes not feasible to detect all the species in a single amplification reaction condition. Here we have established a real-time PCR method that is time and cost effective with a single protocol to detect and distinguish five human Plasmodium species using the existing primers efficiently. The primers used here are being used in the conventional method and the sensitivity as well as specificity of this method has also been immensely improved (100%). The lower limit of detection for Plasmodium falciparum, Plasmodium vivax and Plasmodium malariae are 0.064 parasites/µL, 1.6 parasites/µL, and 0.32 parasites/µL respectively and no cross reactivity was observed. Besides, we have analyzed melt curves that can be used for further species confirmation and validation purposes using multiplex systems. This method, therefore, can be considered as an alternative to the existing lineup for molecular diagnosis of malaria in endemic countries.

Non-human primate and human malaria: past, present and future

Background Studies of the malaria parasites infecting various non-human primates (NHPs) have increased our understanding of the origin, biology and pathogenesis of human Plasmodium parasites. This review considers the major discoveries concerning NHP malaria parasites, highlights their relationships with human malaria and considers the impact that this may have on attempts to eradicate the disease. Results The first description of NHP malaria parasites dates back to the early 20th century. Subsequently, experimental and fortuitous findings indicating that some NHP malaria parasites can be transmitted to humans have raised concerns about the possible impact of a zoonotic malaria reservoir on efforts to control human malaria. Advances in molecular techniques over the last 15 years have contributed greatly to our knowledge of the existence and geographical distribution of numerous Plasmodium species infecting NHPs, and extended our understanding of their close phylogenetic relationships with human malaria parasites. The clinical application of such techniques has also made it possible to document ongoing spillovers of NHP malaria parasites (Plasmodium knowlesi, P. cynomolgi, P. simium, P. brasilianum) in humans living in or near the forests of Asia and South America, thus confirming that zoonotic malaria can undermine efforts to eradicate human malaria. Conclusions Increasing molecular research supports the prophetic intuition of the pioneers of modern malariology who saw zoonotic malaria as a potential obstacle to the full success of malaria eradication programmes. It is, therefore, important to continue surveillance and research based on one-health approaches in order to improve our understanding of the complex interactions between NHPs, mosquito vectors and humans during a period of ongoing changes in the climate and the use of land, monitor the evolution of zoonotic malaria, identify the populations most at risk and implement appropriate preventive strategies.

Dynamics of the Composition of Plasmodium Species Contained within Asymptomatic Malaria Infections in the Central Region of Ghana

Background. Monitoring changes in the composition of the Plasmodium species circulating within the population over a period can inform appropriate treatment recommendations. This study monitored variations in the prevalence of four common human Plasmodium species carried by children with asymptomatic malaria infections over a two-year period. Methods. Two cross-sectional studies were conducted in November 2017 and December 2019. A total of 210 children aged between 4 and 13 years were recruited in 2017, and 164 similarly aged children were recruited in 2019. Approximately 150 μl of finger-pricked blood was used to prepare thick and thin blood smears as well as spot Whatman® #3 filter paper. Genomic DNA was extracted from the dried blood spots and used in PCR to amplify the 18S rRNA gene from four different human Plasmodium parasites. Results. Parasite prevalence by microscopy and the prevalence of P. falciparum detected by PCR was relatively similar at the two time points (Pearson chi-square = 0.405, p = 0.525 , and Pearson chi-square = 0.452, p = 0.501 , respectively). However, the prevalence of PCR detectable P. malariae increased by 8.5-fold, whilst P. ovale increased from 0 to 9% in the children sampled in 2019 relative to the children sampled in 2017. The only parasite species identified by microscopy in this study was P. falciparum, and no P. vivax was identified by either microscopy or PCR in the study population during the study period. Conclusion. There is the need to implement molecular diagnostic tools for malaria parasite surveillance in Ghana. This will enable the identification and treatment of all circulating malaria parasites including P. malariae and P. ovale, whose population is expanding in parts of Ghana including Simiw.

An Integrative Computational Approach for the Prediction of Human-Plasmodium Protein-Protein Interactions

Host-pathogen molecular cross-talks are critical in determining the pathophysiology of a specific infection. Most of these cross-talks are mediated via protein-protein interactions between the host and the pathogen (HP-PPI). Thus, it is essential to know how some pathogens interact with their hosts to understand the mechanism of infections. Malaria is a life-threatening disease caused by an obligate intracellular parasite belonging to the Plasmodium genus, of which P. falciparum is the most prevalent. Several previous studies predicted human-plasmodium protein-protein interactions using computational methods have demonstrated their utility, accuracy, and efficiency to identify the interacting partners and therefore complementing experimental efforts to characterize host-pathogen interaction networks. To predict potential putative HP-PPIs, we use an integrative computational approach based on the combination of multiple OMICS-based methods including human red blood cells (RBC) and Plasmodium falciparum 3D7 strain expressed proteins, domain-domain based PPI, similarity of gene ontology terms, structure similarity method homology identification, and machine learning prediction. Our results reported a set of 716 protein interactions involving 302 human proteins and 130 Plasmodium proteins. This work provides a list of potential human-Plasmodium interacting proteins. These findings will contribute to better understand the mechanisms underlying the molecular determinism of malaria disease and potentially to identify candidate pharmacological targets.