Update on fungal infections of the central nervous system: emerging pathogens and emerging diagnostics

Pathogen-Agnostic Advanced Molecular Diagnostic Testing for Difficult-to-Diagnose Clinical Syndromes-Results of an Emerging Infections Network Survey of Frontline US Infectious Disease Clinicians, May 2023

During routine clinical practice, infectious disease physicians encounter patients with difficult-to-diagnose clinical syndromes and may order advanced molecular testing to detect pathogens. These tests may identify potential infectious causes for illness and allow clinicians to adapt treatments or stop unnecessary antimicrobials. Cases of pathogen-agnostic disease testing also provide an important window into known, emerging, and reemerging pathogens and may be leveraged as part of national sentinel surveillance. A survey of Emerging Infections Network members, a group of infectious disease providers in North America, was conducted in May 2023. The objective of the survey was to gain insight into how and when infectious disease physicians use advanced molecular testing for patients with difficult-to-diagnose infectious diseases, as well as to explore the usefulness of advanced molecular testing and barriers to use. Overall, 643 providers answered at least some of the survey questions; 478 (74%) of those who completed the survey had ordered advanced molecular testing in the last two years, and formed the basis for this study. Respondents indicated that they most often ordered broad-range 16S rRNA gene sequencing, followed by metagenomic next-generation sequencing and whole genome sequencing; and commented that in clinical practice, some, but not all tests were useful. Many physicians also noted several barriers to use, including a lack of national guidelines and cost, while others commented that whole genome sequencing had potential for use in outbreak surveillance. Improving frontline physician access, availability, affordability, and developing clear national guidelines for interpretation and use of advanced molecular testing could potentially support clinical practice and public health surveillance.

ß-D-Glucan Assay in the Cerebrospinal Fluid for the Diagnosis of Non-cryptococcal Fungal Infection of the Central Nervous System: A Retrospective Multicentric Analysis and a Comprehensive Review of the Literature

BACKGROUND

Except for cryptococcosis, fungal infection of the central nervous system (FI-CNS) is a rare but severe complication. Clinical and radiological signs are non-specific, and the value of conventional mycological diagnosis is very low. This study aimed to assess the value of β1,3-D-glucan (BDG) detection in the cerebrospinal fluid (CSF) of non-neonatal non-cryptococcosis patients.

METHODS

Cases associated with BDG assay in the CSF performed in 3 French University Hospitals over 5 years were included. Clinical, radiological, and mycological results were used to classify the episodes as proven/highly probable, probable, excluded, and unclassified FI-CNS. Sensitivity and specificity were compared to that calculated from an exhaustive review of the literature.

RESULTS

In total, 228 episodes consisting of 4, 7, 177, and 40 proven/highly probable, probable, excluded, and unclassified FI-CNS, respectively, were analysed. The sensitivity of BDG assay in CSF to diagnose proven/highly probable/probable FI-CNS ranged from 72.7% [95% confidence interval {CI}: 43.4%‒90.2%] to 100% [95% CI: 51%‒100%] in our study and was 82% in the literature. For the first time, specificity could be calculated over a large panel of pertinent controls and was found at 81.8% [95% CI: 75.3%‒86.8%]. Bacterial neurologic infections were associated with several false positive results.

CONCLUSIONS

Despite its sub-optimal performance, BDG assay in the CSF should be added to the diagnostic armamentarium for FI-CNS.

Nanopore-based metagenomic sequencing for the rapid and precise detection of pathogens among immunocompromised cancer patients with suspected infections

Cancer patients are at high risk of infections and infection-related mortality; thereby, prompt diagnosis and precise anti-infectives treatment are critical. This study aimed to evaluate the performance of nanopore amplicon sequencing in identifying microbial agents among immunocompromised cancer patients with suspected infections. This prospective study enlisted 56 immunocompromised cancer patients with suspected infections. Their body fluid samples such as sputum and blood were collected, and potential microbial agents were detected in parallel by nanopore amplicon sequencing and the conventional culture method. Among the 56 body fluid samples, 47 (83.9%) samples were identified to have at least one pathogen by nanopore amplicon sequencing, but only 25 (44.6%) samples exhibited a positive finding by culture. Among 31 culture-negative samples, nanopore amplicon sequencing successfully detected pathogens in 22 samples (71.0%). Nanopore amplicon sequencing showed a higher sensitivity in pathogen detection than that of the conventional culture method (83.9% vs. 44.6%, P<0.001), and this advantage both existed in blood samples (38.5% vs. 0%, P=0.039) and non-blood samples (97.7% vs. 58.1%, P<0.001). Compared with the culture method, nanopore amplicon sequencing illustrated more samples with bacterial infections (P<0.001), infections from fastidious pathogens (P=0.006), and co-infections (P<0.001). The mean turnaround time for nanopore amplicon sequencing was about 17.5 hours, which was shorter than that of the conventional culture assay. This study suggested nanopore amplicon sequencing as a rapid and precise method for detecting pathogens among immunocompromised cancer patients with suspected infections. The novel and high-sensitive method will improve the outcomes of immunocompromised cancer patients by facilitating the prompt diagnosis of infections and precise anti-infectives treatment.

Giant Central Nervous System Aspergilloma Mimicking Butterfly Neoplasm of the Corpus Callosum

Radiological presentation of central nervous system (CNS) aspergillosis is variable and depends on the immune status of the patients. Typical features of meningoencephalitis, infarction, abscess, and mycotic aneurysms commonly occur in immunocompromised patients. A rare mass-like or tumoral form of cerebral aspergillosis has been described mostly in immunocompetent patients which results in a diagnostic dilemma, thus potentially causing a delay in the management. We present a case of a large CNS aspergilloma mimicking an infiltrative callosal neoplasm in a young immunocompetent patient. Careful evaluation of imaging features, anatomical location, enhancement pattern, concomitant sinonasal and orbital extension, and angio-aggressive nature of the mass lesion with a high index of suspicion can help diagnose CNS aspergillosis in such patients.

Deciphering the role of nanoparticles for management of bacterial meningitis: an update on recent studies

Meningitis is an inflammation of the protective membranes called meninges and fluid adjacent the brain and spinal cord. The inflammatory progression expands all through subarachnoid space of the brain and spinal cord and occupies the ventricles. The pathogens like bacteria, fungi, viruses, or parasites are main sources of infection causing meningitis. Bacterial meningitis is a life-threatening health problem that which needs instantaneous apprehension and treatment. Nesseria meningitidis, Streptococcus pneumoniae, and Haemophilus flu are major widespread factors causing bacterial meningitis. The conventional drug delivery approaches encounter difficulty in crossing this blood-brain barrier (BBB) and therefore are insufficient to elicit the desired pharmacological effect as required for treatment of meningitis. Therefore, application of nanoparticle-based drug delivery systems has become imperative for successful dealing with this deadly disease. The nanoparticles have ability to across BBB via four important transport mechanisms, i.e., paracellular transport, transcellular (transcytosis), endocytosis (adsorptive transcytosis), and receptor-mediated transcytosis. In this review, we reminisce distinctive symptoms of meningitis, and provide an overview of various types of bacterial meningitis, with a focus on its epidemiology, pathogenesis, and pathophysiology. This review describes conventional therapeutic approaches for treatment of meningitis and the problems encountered by them while transmitting across tight junctions of BBB. The nanotechnology approaches like functionalized polymeric nanoparticles, solid lipid nanoparticles, nanostructured lipid carrier, nanoemulsion, liposomes, transferosomes, and carbon nanotubes which have been recently evaluated for treatment or detection of bacterial meningitis have been focused. This review has also briefly summarized the recent patents and clinical status of therapeutic modalities for meningitis.

Encephalitis and Brain Abscess

PURPOSE OF REVIEW

This article reviews infections of the brain parenchyma and includes an overview of the epidemiology, pathogenesis, diagnostic approach, and management of infectious encephalitis and brain abscess.

RECENT FINDINGS

The epidemiology of infectious encephalitis and brain abscess has changed in recent years. Vaccination has reduced the incidence of certain viruses associated with encephalitis, while a decrease in fulminant otogenic infections has led to fewer brain abscesses associated with otitis media. However, changes in climate and human population density and distribution have enabled the emergence of newer pathogens and expanded the geographic range of others, and greater adoption of intensive immunosuppressive regimens for autoimmune conditions has increased the risk of opportunistic infections of the brain. The widespread use of early neuroimaging, along with improved diagnostic methodologies for pathogen detection, newer antimicrobial therapies with better brain penetration, and less invasive neurosurgical techniques, has resulted in better outcomes for patients with infectious encephalitis and brain abscess. Novel technologies including metagenomic next-generation sequencing are increasingly being applied to these conditions in an effort to improve diagnosis. Nevertheless, both infectious encephalitis and brain abscess continue to be associated with substantial mortality.

SUMMARY

Infectious encephalitis and brain abscess can present as neurologic emergencies and require rapid assessment, thorough and appropriate diagnostic testing, and early initiation of empiric therapies directed against infectious agents. Close clinical follow-up, proper interpretation of diagnostic results, and appropriate tailoring of therapeutic agents are essential to optimizing outcomes. Diagnosis and management of parenchymal brain infections are complex and often best achieved with a multidisciplinary care team involving neurologists, neurosurgeons, neuroradiologists, infectious disease physicians, and pathologists.

Successful Isavuconazole Salvage Therapy for a Cryptococcus deuterogattii (AFLP6/VGII) Disseminated Infection in a European Immunocompetent Patient

Members of the Cryptococcus gattii species complex are notorious causes of cryptococcosis as they often cause severe, life-threatening infections. Here we describe a case of a severe disseminated C. deuterogattii infection in a previously healthy patient who was initially treated with amphotericin B, 5-fluorocytosine and fluconazole, which led to a good neurological response, but the infection in the lungs remained unaltered and was not completely resolved until switching the antifungal therapy to isavuconazole. The infection was likely acquired during a one-month stay at the Azores Islands, Portugal. Environmental sampling did not yield any cryptococcal isolate; therefore, the source of this apparent autochthonous case could not be determined. Molecular typing showed that the cultured C. deuterogattii isolates were closely related to the Vancouver Island outbreak-genotype.

Systems Biology Approaches for Therapeutics Development Against COVID-19

Understanding the systems biology approaches for promoting the development of new therapeutic drugs is attaining importance nowadays. The threat of COVID-19 outbreak needs to be vanished for global welfare, and every section of research is focusing on it. There is an opportunity for finding new, quick, and accurate tools for developing treatment options, including the vaccine against COVID-19. The review at this moment covers various aspects of pathogenesis and host factors for exploring the virus target and developing suitable therapeutic solutions through systems biology tools. Furthermore, this review also covers the extensive details of multiomics tools i.e., transcriptomics, proteomics, genomics, lipidomics, immunomics, and in silico computational modeling aiming towards the study of host-virus interactions in search of therapeutic targets against the COVID-19.

Fatal Case of Cerebral Aspergillum in an Immunocompetent Patient

Introduction: Cerebral aspergillum is rare and usually misdiagnosed because its presentation mimics tuberculous meningitis, brain abscess, or tumor. The diagnosis and treatment of central nervous system (CNS) infections due to Aspergillus are very difficult because accurate diagnosis is often made intra-operatively. Case Presentation: Here, we report a case of cerebral aspergilloma in an immunocompetent host. A 35-year-old man admitted with progressive left hemifacial paresthesia followed by severe pain in trigeminal nerve territory. On physical examination, except for fifth nerve palsy and difficult mastication, there was not any sensory and motor deficit. Magnetic resonance imaging (MRI) of the brain showed T1 iso and T2 low signal lesion in the left parasellar region with enhancement. The lesion is extended to the left side of the prepontine cistern in the course of trigeminal nerve, craniotomy, and total surgical resection of the mass was performed. Isolated brain lesion and the pathology from stereotactic biopsy confirmed cerebral aspergillosis. The result of testing for human immunodeficiency virus (HIV) was negative. Although the patient had two subsequent recurrences, at first, good outcome was achieved by treatment with a combination of surgical intervention, and antifungal amphotericin B deoxycholate was administered, then changed to voriconazole. Unfortunately, after two years, he experienced new progressive symptoms, and the patient died despite several reoperations due to malfunctioning of external ventricle devices as well as the treatment of recurrent post-operation meningitis and voriconazole therapy. Conclusions: Most cases of intracranial aspergillosis show that this infection is pathogenic in immunocompromised hosts; however, in some cases, invasive Aspergillus was reported as an opportunistic infection in immunocompetent patients. In these patients, though primary cranial aspergillosis is very rare, it is possible that isolated brain involvement in a previously healthy case may be explained by unknown defects in immune pathways or massive exposure to spores.

Nanotechnology-Based Diagnostics and Therapy for Pathogen-Related Infections in the CNS

The central nervous system (CNS) encompasses the brain, spinal cord, and nerves, where both brain and spinal cord are safeguarded by the meninges. However, serious bacterial, viral, or fungal infection in the brain causes life-threatening diseases such as meningitis. Engineered nanostructures hold great promise for not only in the diagnosis but also for combating microbial drug resistance owing to their high surface area and innate antibacterial activity. We delineate several nanoparticle-based approaches to enhance the CNS delivery of drugs across the blood-brain barrier (BBB). While pathogens invade the CNS by phagocytosis or receptor (e.g., EphA2)-mediated transcytosis, most of the nanoparticles cross the BBB via receptor-mediated transcytosis (e.g., antibody, peptide, protein). We also provide our perspectives on the diagnostic pathways based on nanotechnology for the detection of pathogens in the brain, thereby opening up new therapeutic avenues.

The Neurotropic Black Yeast Exophiala dermatitidis Induces Neurocytotoxicity in Neuroblastoma Cells and Progressive Cell Death

The neurotropic and extremophilic black yeast Exophiala dermatitidis (Herpotrichellaceae) inhabits diverse indoor environments, in particular bathrooms, steam baths, and dishwashers. Here, we show that the selected strain, EXF-10123, is polymorphic, can grow at 37 °C, is able to assimilate aromatic hydrocarbons (toluene, mineral oil, n-hexadecane), and shows abundant growth with selected neurotransmitters (acetylcholine, gamma-aminobutyric acid, glycine, glutamate, and dopamine) as sole carbon sources. We have for the first time demonstrated the effect of E. dermatitidis on neuroblastoma cell model SH-SY5Y. Aqueous and organic extracts of E. dermatitidis biomass reduced SH-SY5Y viability by 51% and 37%, respectively. Melanized extracellular vesicles (EVs) prepared from this strain reduced viability of the SH-SY5Y to 21%, while non-melanized EVs were considerably less neurotoxic (79% viability). We also demonstrated direct interactions of E. dermatitidis with SH-SY5Y by scanning electron and confocal fluorescence microscopy. The observed invasion and penetration of neuroblastoma cells by E. dermatitidis hyphae presumably causes the degradation of most neuroblastoma cells in only three days. This may represent a so far unknown indirect or direct cause for the development of some neurodegenerative diseases such as Alzheimer’s.

A Cross-Sectional Study of Hyponatremia Associated with Acute Central Nervous System Infections

Hyponatremia can occur with central nervous system (CNS) infections, but the frequency and severity may depend on the organism and nature of CNS involvement. In this cross-sectional study at a large Australian hospital network from 2015 to 2018, we aimed to determine the prevalence and severity of hyponatremia associated with CNS infection clinical syndromes, and the association with specific organisms. We examined the results of cerebrospinal fluid analysis from lumbar punctures performed in 184 adult patients with a serum sodium below 135 mmol/L who had abnormal cerebrospinal fluid analysis and a clinical syndrome consistent with an acute CNS infection (meningitis or encephalitis). Hyponatremia affected 39% of patients and was more severe and frequent in patients with encephalitis compared to meningitis (odds ratio = 3.03, 95% CI: 1.43–6.39, after adjusting for age). Hyponatremia was present on admission in 85% of cases. Herpes simplex virus infection was associated with the highest odds of hyponatremia (odds ratio = 3.25, 95% CI: 1.13–7.87) while enterovirus infection was associated with the lowest (odds ratio = 0.36, 95% CI: 0.14–0.92), compared to cases without an isolated organism. We concluded that the risk of hyponatremia may vary by the organism isolated but the clinical syndrome was a useful surrogate for predicting the probability of developing hyponatremia.