A patient with granulomatous amoebic encephalitis caused by Balamuthia mandrillaris survived with two excisions and medication

Modelling amoebic brain infection caused by Balamuthia mandrillaris using a human cerebral organoid

The lack of disease models adequately resembling human tissue has hindered our understanding of amoebic brain infection. Three-dimensional structured organoids provide a microenvironment similar to human tissue. This study demonstrates the use of cerebral organoids to model a rare brain infection caused by the highly lethal amoeba Balamuthia mandrillaris. Cerebral organoids were generated from human pluripotent stem cells and infected with clinically isolated B. mandrillaris trophozoites. Histological examination showed amoebic invasion and neuron damage following coculture with the trophozoites. The transcript profile suggested an alteration in neuron growth and a proinflammatory response. The release of intracellular proteins specific to neuronal bodies and astrocytes was detected at higher levels postinfection. The amoebicidal effect of the repurposed drug nitroxoline was examined using the human cerebral organoids. Overall, the use of human cerebral organoids was important for understanding the mechanism of amoeba pathogenicity, identify biomarkers for brain injury, and in the testing of a potential amoebicidal drug in a context similar to the human brain.

Balamuthia mandrillaris amoebic encephalitis mimicking tuberculous meningitis

A 76-year-old female with no apparent immunosuppressive conditions and no history of exposure to freshwater and international travel presented with headache and nausea 3 weeks before the presentation. On admission, her consciousness was E4V4V6. Cerebrospinal fluid analysis showed pleocytosis with mononuclear cell predominance, elevated protein, and decreased glucose. Despite antibiotic and antiviral therapy, her consciousness and neck stiffness gradually worsened, right eye-movement restriction appeared, and the right direct light reflex became absent. Brain magnetic resonance imaging revealed hydrocephalus in the inferior horn of the left lateral ventricle and meningeal enhancement around the brainstem and cerebellum. Tuberculous meningitis was suspected, and pyrazinamide, ethambutol, rifampicin, isoniazid, and dexamethasone were started. In addition, endoscopic biopsy was performed from the white matter around the inferior horn of the left lateral ventricle to exclude brain tumor. A brain biopsy specimen revealed eosinophilic round cytoplasm with vacuoles around blood vessels, and we diagnosed with amoebic encephalitis. We started azithromycin, flucytosine, rifampicin, and fluconazole, but her symptoms did not improve. She died 42 days after admission. In autopsy, the brain had not retained its structure due to autolysis. Hematoxylin and eosin staining of her brain biopsy specimen showed numerous amoebic cysts in the perivascular brain tissue. Analysis of the 16S ribosomal RNA region of amoebas from brain biopsy and autopsy specimens revealed a sequence consistent with Balamuthia mandrillaris. Amoebic meningoencephalitis can present with features characteristic of tuberculous meningitis, such as cranial nerve palsies, hydrocephalus, and basal meningeal enhancement. Difficulties in diagnosing amoebic meningoencephalitis are attributed to the following factors: (1) excluding tuberculous meningitis by microbial testing is difficult, (2) amoebic meningoencephalitis has low incidence and can occur without obvious exposure history, (3) invasive brain biopsy is essential in diagnosing amoebic meningoencephalitis. We should recognize the possibility of amoebic meningoencephalitis when evidence of tuberculosis meningitis cannot be demonstrated.

Phenotypic assay for cytotoxicity assessment of Balamuthia mandrillaris against human neurospheroids

Introduction

The phenotypic screening of drugs against Balamuthia mandrillaris, a neuropathogenic amoeba, involves two simultaneous phases: an initial step to test amoebicidal activity followed by an assay for cytotoxicity to host cells. The emergence of three-dimensional (3D) cell cultures has provided a more physiologically relevant model than traditional 2D cell culture for studying the pathogenicity of B. mandrillaris. However, the measurement of ATP, a critical indicator of cell viability, is complicated by the overgrowth of B. mandrillaris in coculture with host cells during drug screening, making it challenging to differentiate between amoebicidal activity and drug toxicity to human cells.

Methods

To address this limitation, we introduce a novel assay that utilizes three-dimensional hanging spheroid plates (3DHSPs) to evaluate both activities simultaneously on a single platform.

Results and discussion

Our study showed that the incubation of neurospheroids with clinically isolated B. mandrillaris trophozoites resulted in a loss of neurospheroid integrity, while the ATP levels in the neurospheroids decreased over time, indicating decreased host cell viability. Conversely, ATP levels in isolated trophozoites increased, indicating active parasite metabolism. Our findings suggest that the 3DHSP-based assay can serve as an endpoint for the phenotypic screening of drugs against B. mandrillaris, providing a more efficient and accurate approach for evaluating both parasite cytotoxicity and viability.

Amebic encephalitis and meningoencephalitis: an update on epidemiology, diagnostic methods, and treatment

PURPOSE OF REVIEW

Free-living amebae (FLA) including Naegleria fowleri , Balamuthia mandrillaris , and Acanthamoeba species can cause rare, yet severe infections that are nearly always fatal. This review describes recent developments in epidemiology, diagnosis, and treatment of amebic meningoencephalitis.

RECENT FINDINGS

Despite similarities among the three pathogenic FLA, there are notable variations in disease presentations, routes of transmission, populations at risk, and outcomes for each. Recently, molecular diagnostic tools have been used to diagnose a greater number of FLA infections. Treatment regimens for FLA have historically relied on survivor reports; more data is needed about novel treatments, including nitroxoline.

SUMMARY

Research to identify new drugs and guide treatment regimens for amebic meningoencephalitis is lacking. However, improved diagnostic capabilities may lead to earlier diagnoses, allowing earlier treatment initiation and improved outcomes. Public health practitioners should continue to prioritize increasing awareness and providing education to clinicians, laboratorians, and the public about amebic infections.

Pathogenic free-living amoebic encephalitis from 48 cases in China: A systematic review

Background

Free-living amoebae (FLA) including Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris can become pathogenic and cause severe cerebral infections, named primary amoebic meningoencephalitis (PAM), granulomatous amoebic encephalitis (GAE), and balamuthia amoebic encephalitis (BAE), respectively. FLA encephalitis has been reported across China, but the clinical data descriptions and analytical results of these different reports vary widely. Currently, no consensus treatment has been established. We conduct a systematic review to evaluate the exposure location, clinical symptoms, diagnosis, treatment, and prognosis of three FLA encephalitis and aim to reveal the differences between three FLA encephalitis in China.

Methods

We used MEDLINE (PubMed interface), EMBASE, China National Knowledge Infrastructure (CNKI), Wanfang database, and China Biology Medicine disc (CBMdisc) databases for literatures published and manually retrieve the hospital records of our hospital. The search time was up to August 30, 2022, with no language restrictions.

Results

After excluding possible duplicate cases, a total of 48 patients of three FLA encephalitis were collected. One from the medical records of our hospital and 47 patients from 31 different studies. There were 11 patients of PAM, 10 patients of GAE, and 27 patients of BAE. The onset of PAM is mostly acute or subacute, and the clinical symptoms are acute and fulminant hemorrhagic meningoencephalitis. Most patients with GAE and BAE have an insidious onset and a chronic course. A total of 21 BAE patients (77.8%) had skin lesions before onset of symptoms. Additionally, 37 cases (77.1%) were diagnosed with FLA encephalitis before death. And there were 4 of PAM, 2 of GAE, and 10 of BAE diagnosed using next generation sequencing. No single agent can be proposed as the ideal therapy by itself. Only 6 cases were successfully treated.

Conclusions

This review provides an overview of the available data and studies of FLA encephalitis in China and identify some potential differences. FLA encephalitis is a rare but pathogenic infection, and physicians should early identify this encephalitis to improve survival.

Distribution and Current State of Molecular Genetic Characterization in Pathogenic Free-Living Amoebae

Free-living amoebae (FLA) are protozoa widely distributed in the environment, found in a great diversity of terrestrial biomes. Some genera of FLA are linked to human infections. The genus Acanthamoeba is currently classified into 23 genotypes (T1-T23), and of these some (T1, T2, T4, T5, T10, T12, and T18) are known to be capable of causing granulomatous amoebic encephalitis (GAE) mainly in immunocompromised patients while other genotypes (T2, T3, T4, T5, T6, T10, T11, T12, and T15) cause Acanthamoeba keratitis mainly in otherwise healthy patients. Meanwhile, Naegleria fowleri is the causative agent of an acute infection called primary amoebic meningoencephalitis (PAM), while Balamuthia mandrillaris, like some Acanthamoeba genotypes, causes GAE, differing from the latter in the description of numerous cases in patients immunocompetent. Finally, other FLA related to the pathologies mentioned above have been reported; Sappinia sp. is responsible for one case of amoebic encephalitis; Vermamoeba vermiformis has been found in cases of ocular damage, and its extraordinary capacity as endocytobiont for microorganisms of public health importance such as Legionella pneumophila, Bacillus anthracis, and Pseudomonas aeruginosa, among others. This review addressed issues related to epidemiology, updating their geographic distribution and cases reported in recent years for pathogenic FLA.