Maturation of Plasmodium falciparum in multiply infected erythrocytes and the potential role in malaria pathogenesis

F-erythrocytes promote Plasmodium falciparum proliferation in sickle cell disease

BACKGROUND

Sickle cell disease (SCD) remains prevalent because heterozygous carriers (HbAS) are partially resistant to Plasmodium falciparum malaria. Sickle hemoglobin (HbS) polymerization in low and intermediate oxygen (O2 ) conditions is the main driver of HbAS-driven resistance to P. falciparum malaria. However, epidemiological studies have reported mixed malaria morbidity and mortality outcomes in individuals with sickle cell disease (SCD). While maximum-tolerated dose hydroxyurea has been shown to lower malaria incidence, fetal hemoglobin (HbF), an inhibitor of HbS polymerization that is variably packaged in F-erythrocytes, might provide hemoglobin that is accessible to the parasite for feeding.

METHODS

To explore that risk, we examined the effect of variable mean corpuscular fetal hemoglobin (MCHF) on P. falciparum proliferation, invasion, and development in HbSS RBCs.

RESULTS

We found that greater MCHF in HbSS red blood cells (RBCs) is associated with increased P. falciparum proliferation in O2 environments comparable with the microcirculation. Moreover, both parasite invasion and intracellular growth, the major components of proliferation, occur predominantly in F-erythrocytes and are augmented with increasing MCHF.

CONCLUSIONS

HbF modifies P. falciparum infection in HbSS RBCs, further highlighting the complexity of the molecular interactions between these two diseases. Other inhibitors of HbS polymerization that do not increase HbF or F-erythrocytes should be independently assessed for their effects on P. falciparum malaria proliferation in HbSS RBCs.

Correlation of parasite density and biochemical parameters in children with malaria infection in Calabar, South-South Nigeria

Background

Malaria parasitemia is associated with premature, excessive hemolysis, induction of oxidative stress, and derangement in metabolism of iron, proteins, and some electrolytes. This study aims to evaluate the effects of malaria infection on ascorbic acid (AA), uric acid (UA), iron, transferrin, albumin, total iron-binding capacity (TIBC), calcium, and magnesium levels in malaria infection.

Results

Among the 50 malaria-infected children, 12 had severe parasitemia (PD ≥ 10,000 parasites/μl), 16 had moderate parasitemia (PD: 2000 to < 10,000 parasites/μl), and 22 children had mild parasitemia (PD < 2000 parasites/μl). The AA, iron, transferrin, and TIBC levels were significantly lower and UA and Mg higher in malaria-infected children compared with the controls. Ascorbic acid correlated negatively with UA and PD in malaria-infected children. Iron correlated positively with albumin, transferrin, and TIBC in malaria-infected children, while Ca correlated negatively with Mg levels.

Conclusion

Malaria infection in children is associated with reduced AA and iron parameters and increased UA and Mg levels; hence, vitamin C and iron supplementation could be useful in malaria therapy.

The Rough Guide to Monocytes in Malaria Infection

While half of the world's population is at risk of malaria, the most vulnerable are still children under five, pregnant women and returning travelers. Anopheles mosquitoes transmit malaria parasites to the human host; but how Plasmodium interact with the innate immune system remains largely unexplored. The most recent advances prove that monocytes are a key component to control parasite burden and to protect host from disease. Monocytes' protective roles include phagocytosis, cytokine production and antigen presentation. However, monocytes can be involved in pathogenesis and drive inflammation and sequestration of infected red blood cells in organs such as the brain, placenta or lungs by secreting cytokines that upregulate expression of endothelial adhesion receptors. Plasmodium DNA, hemozoin or extracellular vesicles can impair the function of monocytes. With time, reinfections with Plasmodium change the relative proportion of monocyte subsets and their physical properties. These changes relate to clinical outcomes and might constitute informative biomarkers of immunity. More importantly, at the molecular level, transcriptional, metabolic or epigenetic changes can “prime” monocytes to alter their responses in future encounters with Plasmodium. This mechanism, known as trained immunity, challenges the traditional view of monocytes as a component of the immune system that lacks memory. Overall, this rough guide serves as an update reviewing the advances made during the past 5 years on understanding the role of monocytes in innate immunity to malaria.

Host-mediated selection impacts the diversity of Plasmodium falciparum antigens within infections

Host immunity exerts strong selective pressure on pathogens. Population-level genetic analysis can identify signatures of this selection, but these signatures reflect the net selective effect of all hosts and vectors in a population. In contrast, analysis of pathogen diversity within hosts provides information on individual, host-specific selection pressures. Here, we combine these complementary approaches in an analysis of the malaria parasite Plasmodium falciparum using haplotype sequences from thousands of natural infections in sub-Saharan Africa. We find that parasite genotypes show preferential clustering within multi-strain infections in young children, and identify individual amino acid positions that may contribute to strain-specific immunity. Our results demonstrate that natural host defenses to P. falciparum act in an allele-specific manner to block specific parasite haplotypes from establishing blood-stage infections. This selection partially explains the extreme amino acid diversity of many parasite antigens and suggests that vaccines targeting such proteins should account for allele-specific immunity.

Host immune responses exert selective pressure on Plasmodium falciparum. Here, the authors show that allele-specific immunity impacts the antigenic diversity of individual malaria infections. This process partially explains the extreme amino acid diversity of many parasite antigens and suggests that vaccines should account for allele-specific immunity.

Leptospirosis: Molecular trial path and immunopathogenesis correlated with dengue, malaria and mimetic hemorrhagic infections

Immuno-pathogenesis of leptospirosis can be recounted well by following its trail path from entry to exit, while inducing disastrous damages in various tissues of the host. Dysregulated, inappropriate and excessive immune responses are unanimously blamed in fatal leptospirosis. The inherent abilities of the pathogen and inabilities of the host were debated targeting the severity of the disease. Hemorrhagic manifestation through various mechanisms leading to a fatal end is observed when this disease is unattended. The similar vascular destructions and hemorrhage manifestations are noted in infections with different microbes in endemic areas. The simultaneous infection in a host with more than one pathogen or parasite is referred as the coinfection. Notably, common endemic infections such as leptospirosis, dengue, chikungunya, and malaria, harbor favorable environments to flourish in similar climates, which is aggregated with stagnated water and aggravated with the poor personal and environmental hygiene of the inhabitants. These factors aid the spread of pathogens and parasites to humans and potential vectors, eventually leading to outbreaks of public health relevance. Malaria, dengue and chikungunya need mosquitoes as vectors, in contrast with leptospirosis, which directly invades human, although the environmental bacterial load is maintained through other mammals, such as rodents. The more complicating issue is that infections by different pathogens exhibiting similar symptoms but require different treatment management. The current review explores different pathogens expressing specific surface proteins and their ability to bind with array of host proteins with or without immune response to enter into the host tissues and their ability to evade the host immune responses to invade and their affinity to certain tissues leading to the common squeal of hemorrhage. Furthermore, at the host level, the increased susceptibility and inability of the host to arrest the pathogens' and parasites' spread in different tissues, various cytokines accumulated to eradicate the microorganisms and their cellular interactions, the antibody dependent defense and the susceptibility of individual organs bringing the manifestation of the diseases were explored. Lastly, we provided a discussion on the immune trail path of pathogenesis from entry to exit to narrate the similarities and dissimilarities among various hemorrhagic fevers mentioned above, in order to outline future possibilities of prevention, diagnosis, and treatment of coinfections, with special reference to endemic areas.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.