Intestinal injury and the gut microbiota in patients with Plasmodium falciparum malaria

The pathophysiology of severe falciparum malaria involves a complex interaction between the host, parasite, and gut microbes. In this review, we focus on understanding parasite-induced intestinal injury and changes in the human intestinal microbiota composition in patients with Plasmodium falciparum malaria. During the blood stage of P. falciparum infection, infected red blood cells adhere to the vascular endothelium, leading to widespread microcirculatory obstruction in critical tissues, including the splanchnic vasculature. This process may cause intestinal injury and gut leakage. Epidemiological studies indicate higher rates of concurrent bacteraemia in severe malaria cases. Furthermore, severe malaria patients exhibit alterations in the composition and diversity of the intestinal microbiota, although the exact contribution to pathophysiology remains unclear. Mouse studies have demonstrated that the gut microbiota composition can impact susceptibility to Plasmodium infections. In patients with severe malaria, the microbiota shows an enrichment of pathobionts, including pathogens that are known to cause concomitant bloodstream infections. Microbial metabolites have also been detected in the plasma of severe malaria patients, potentially contributing to metabolic acidosis and other clinical complications. However, establishing causal relationships requires intervention studies targeting the gut microbiota

Identifying prognostic factors of severe metabolic acidosis and uraemia in African children with severe falciparum malaria: a secondary analysis of a randomized trial.

BACKGROUND: Severe metabolic acidosis and acute kidney injury are major causes of mortality in children with severe malaria but are often underdiagnosed in low resource settings. METHODS: A retrospective analysis of the 'Artesunate versus quinine in the treatment of severe falciparum malaria in African children' (AQUAMAT) trial was conducted to identify clinical features of severe metabolic acidosis and uraemia in 5425 children from nine African countries. Separate models were fitted for uraemia and severe metabolic acidosis. Separate univariable and multivariable logistic regression were performed to identify prognostic factors for severe metabolic acidosis and uraemia. Both analyses adjusted for the trial arm. A forward selection approach was used for model building of the logistic models and a threshold of 5% statistical significance was used for inclusion of variables into the final logistic model. Model performance was assessed through calibration, discrimination, and internal validation with bootstrapping. RESULTS: There were 2296 children identified with severe metabolic acidosis and 1110 with uraemia. Prognostic features of severe metabolic acidosis among them were deep breathing (OR: 3.94, CI 2.51-6.2), hypoglycaemia (OR: 5.16, CI 2.74-9.75), coma (OR: 1.72 CI 1.17-2.51), respiratory distress (OR: 1.46, CI 1.02-2.1) and prostration (OR: 1.88 CI 1.35-2.59). Features associated with uraemia were coma (3.18, CI 2.36-4.27), Prostration (OR: 1.78 CI 1.37-2.30), decompensated shock (OR: 1.89, CI 1.31-2.74), black water fever (CI 1.58. CI 1.09-2.27), jaundice (OR: 3.46 CI 2.21-5.43), severe anaemia (OR: 1.77, CI 1.36-2.29) and hypoglycaemia (OR: 2.77, CI 2.22-3.46) CONCLUSION: Clinical and laboratory parameters representing contributors and consequences of severe metabolic acidosis and uraemia were independently associated with these outcomes. The model can be useful for identifying patients at high risk of these complications where laboratory assessments are not routinely available

Improving disseminated histoplasmosis diagnosis in HIV/AIDS patients in Suriname: The role of a urine lateral flow assay

Histoplasmosis is a frequent cause of infections in people living with HIV/AIDS (PLWHA). This study introduces the application of a Histoplasma capsulatum urine antigen lateral flow assay (LFA) for diagnosing disseminated histoplasmosis in PLWHA in Suriname. The LFA's diagnostic accuracy was compared with the current diagnostic approach, aiming to assess whether this test resulted in improved early detection and management. Additionally, the prevalence of histoplasmosis among advanced stage HIV patients without clinical suspicion of infection was evaluated using the same LFA. In total, 98 patients were included in the study, of which 58 were classified as "possible disseminated histoplasmosis (DH)" based on clinical criteria and 40 as "controls". Of these possible DH cases, only 19 (32.7%) had a positive LFA. During the study, decisions for treatment were made without the treating physician being aware of the LFA result. Only 55% of the patients who started treatment for histoplasmosis based on clinical criteria had a positive LFA, and 21% of untreated patients had a positive LFA. This study shows that combining clinical signs with LFA results enhances diagnostic accuracy and is cost effective, resulting in better treatment decisions

Rickettsial illnesses as important causes of febrile illness in Chittagong, Bangladesh

We conducted a yearlong prospective study of febrile patients admitted to a tertiary referral hospital in Chittagong, Bangladesh, to assess the proportion of patients with rickettsial illnesses and identify the causative pathogens, strain genotypes, and associated seasonality patterns. We diagnosed scrub typhus in 16.8% (70/416) and murine typhus in 5.8% (24/416) of patients; 2 patients had infections attributable to undifferentiated Rickettsia spp. and 2 had DNA sequence-confirmed R. felis infection. Orientia tsutsugamushi genotypes included Karp, Gilliam, Kato, and TA763-like strains, with a prominence of Karp-like strains. Scrub typhus admissions peaked in a biphasic pattern before and after the rainy season, whereas murine typhus more frequently occurred before the rainy season. Death occurred in 4% (18/416) of cases; case-fatality rates were 4% each for scrub typhus (3/70) and murine typhus (1/28). Overall, 23.1% (96/416) of patients had evidence of treatable rickettsial illnesses, providing important evidence toward optimizing empirical treatment strategies

Metabolomic characterisation of acidosis in severe falciparum malaria

Severe falciparum malaria is a potentially lethal parasitic infection for which the treatment remains suboptimal as the pathophysiology is incompletely understood. Acidosis is the strongest predictor of death, caused by an accumulation of acids of which some are known, such as L-lactate, while others remain unidentified. The aim of this thesis was to further characterise metabolic acidosis in severe falciparum malaria by establishing the identity and source of the unidentified non-lactate acid load. A prospective observational study was conducted among patients with falciparum malaria from Bangladesh to establish the identity of metabolites associated with acidosis through a metabolomic analysis of plasma of 152 participants (Chapter 3). Patients with acidosis had significantly elevated levels of organic acids in their plasma that could be traced to a potential microbial source, either parasitic or bacterial. Additionally, dysregulation of plasma free amino acids was observed. The clearance of newly identified microbial acids was impaired in fatal cases. Follow-up studies were conducted by performing an in vitro metabolomic analysis of the liquid culture medium of Plasmodium falciparum 3D7 strain parasites with the aim to determine if parasites produce any of the microbial acids identified in patients with severe malaria (Chapter 4). There was no evidence for the release of microbial acids by Pf 3D7 in vitro suggesting their source is unlikely to be parasitic. Alongside of this, a prospective study was done to determine factors related to plasma free amino acid dysregulation (Chapter 5). Amino acids were simultaneously quantified in the plasma of 295 participants in relation to clinical syndromes. It was observed that amino acid abnormalities were part of widespread fluctuations in nitrogen balance, whereby the direction of change was related to the severity of malarial disease and the presence of hyperlactataemia, reflecting underlying tissue hypoxia. Finally, the role of the gut microbiota was further investigated as a potential source of microbial acids in 86 participants, including cases with severe falciparum malaria acidosis, by measuring soluble markers of gut integrity in plasma and sequencing the V4 region of the 16S rRNA gene in faecal DNA (Chapter 6). Patients with malaria had signs of impaired gut barrier function with elevated levels of plasma D-lactate linked to an enrichment of lactate-producing species in the gut microbiota. In conclusion, acidosis in severe falciparum malaria is associated with microbial acids and plasma free amino acid derangements. Microbial acids are not produced by Pf3D7 in vitro but instead might derive from the gut microbiota. These findings point towards a leaky gut as a possible source of previously unidentified acids in severe falciparum malaria acidosis with potential implications for treatment.</p

Metabolomic characterisation of acidosis in severe falciparum malaria

Severe falciparum malaria is a potentially lethal parasitic infection for which the treatment remains suboptimal as the pathophysiology is incompletely understood. Acidosis is the strongest predictor of death, caused by an accumulation of acids of which some are known, such as L-lactate, while others remain unidentified. The aim of this thesis was to further characterise metabolic acidosis in severe falciparum malaria by establishing the identity and source of the unidentified non-lactate acid load. A prospective observational study was conducted among patients with falciparum malaria from Bangladesh to establish the identity of metabolites associated with acidosis through a metabolomic analysis of plasma of 152 participants (Chapter 3). Patients with acidosis had significantly elevated levels of organic acids in their plasma that could be traced to a potential microbial source, either parasitic or bacterial. Additionally, dysregulation of plasma free amino acids was observed. The clearance of newly identified microbial acids was impaired in fatal cases. Follow-up studies were conducted by performing an in vitro metabolomic analysis of the liquid culture medium of Plasmodium falciparum 3D7 strain parasites with the aim to determine if parasites produce any of the microbial acids identified in patients with severe malaria (Chapter 4). There was no evidence for the release of microbial acids by Pf 3D7 in vitro suggesting their source is unlikely to be parasitic. Alongside of this, a prospective study was done to determine factors related to plasma free amino acid dysregulation (Chapter 5). Amino acids were simultaneously quantified in the plasma of 295 participants in relation to clinical syndromes. It was observed that amino acid abnormalities were part of widespread fluctuations in nitrogen balance, whereby the direction of change was related to the severity of malarial disease and the presence of hyperlactataemia, reflecting underlying tissue hypoxia. Finally, the role of the gut microbiota was further investigated as a potential source of microbial acids in 86 participants, including cases with severe falciparum malaria acidosis, by measuring soluble markers of gut integrity in plasma and sequencing the V4 region of the 16S rRNA gene in faecal DNA (Chapter 6). Patients with malaria had signs of impaired gut barrier function with elevated levels of plasma D-lactate linked to an enrichment of lactate-producing species in the gut microbiota. In conclusion, acidosis in severe falciparum malaria is associated with microbial acids and plasma free amino acid derangements. Microbial acids are not produced by Pf3D7 in vitro but instead might derive from the gut microbiota. These findings point towards a leaky gut as a possible source of previously unidentified acids in severe falciparum malaria acidosis with potential implications for treatment.</p

Antimicrobial drug resistance among clinically relevant bacterial isolates in sub-Saharan Africa: a systematic review

Little is known about the prevalence of antimicrobial resistance (AMR) amongst bacterial pathogens in sub-Saharan Africa (sSA), despite calls for continent-wide surveillance to inform empirical treatment guidelines. We searched PubMed and additional databases for susceptibility data of key pathogens for surveillance, published between 1990 and 2013. Extracted data were standardized to a prevalence of resistance in populations of isolates and reported by clinical syndrome, microorganism, relevant antimicrobial drugs and region. We identified 2005 publications, of which 190 were analysed. Studies predominantly originated from east sSA (61%), were hospital based (60%), were from an urban setting (73%) and reported on isolates from patients with a febrile illness (42%). Quality procedures for susceptibility testing were described in <50% of studies. Median prevalence (MP) of resistance to chloramphenicol in Enterobacteriaceae, isolated from patients with a febrile illness, ranged between 31.0% and 94.2%, whilst MP of resistance to third-generation cephalosporins ranged between 0.0% and 46.5%. MP of resistance to nalidixic acid in Salmonella enterica Typhi ranged between 15.4% and 43.2%. The limited number of studies providing prevalence data on AMR in Gram-positive pathogens or in pathogens isolated from patients with a respiratory tract infection, meningitis, urinary tract infection or hospital-acquired infection suggested high prevalence of resistance to chloramphenicol, trimethoprim/sulfamethoxazole and tetracycline and low prevalence to third-generation cephalosporins and fluoroquinolones. Our results indicate high prevalence of AMR in clinical bacterial isolates to antimicrobial drugs commonly used in sSA. Enhanced approaches for AMR surveillance are needed to support empirical therapy in sS

Host innate immune responses to sepsis

The immune response to sepsis can be seen as a pattern recognition receptor-mediated dysregulation of the immune system following pathogen invasion in which a careful balance between inflammatory and anti-inflammatory responses is vital. Invasive infection triggers both pro-inflammatory and anti-inflammatory host responses, the magnitude of which depends on multiple factors, including pathogen virulence, site of infection, host genetics, and comorbidities. Toll-like receptors, the inflammasomes, and other pattern recognition receptors initiate the immune response after recognition of danger signals derived from microorganisms, so-called pathogen-associated molecular patterns or derived from the host, so-called danger-associated molecular patterns. Further dissection of the role of host-pathogen interactions, the cytokine response, the coagulation cascade, and their multidirectional interactions in sepsis should lead toward the development of new therapeutic strategies in sepsi