A case of primary amebic meningoencephalitis caused by Naegleria fowleri in Bangladesh

Therapeutic glycan-specific antibody binding mediates protection during primary amoebic meningoencephalitis

Naegleria fowleri (N. fowleri) infection via the upper respiratory tract causes a fatal CNS disease known as primary amoebic meningoencephalitis (PAM). The robust in vivo immune response to N. fowleri infection underlies the immunopathology that characterizes the disease. However, little is known about why this pathogen evades immune control. Infections occur in seemingly healthy individuals and effective clinical options are lacking, thus a nearly 98% fatality rate. It is unclear how or if host factors may contribute to susceptibility or disease exacerbation, yet mechanistic studies of the in vivo immune response and disease progression are hampered by a lack of tools. In this study, we have generated monoclonal antibodies to N. fowleri surface antigens and shown them to be excellent tools for studying the in vivo immune response. We also identified one monoclonal, 2B6, with potent inherent anti-amoebastatic activity in vitro. This antibody is also able to therapeutically prolong host survival in vivo and furthermore, recombinant antibodies with an isotype more capable of directing immune effector activity further improved survival when given therapeutically. Thus, we report the generation of a novel monoclonal antibody to N. fowleri that can enhance beneficial immune functions, even when given therapeutically during disease. We believe this provides evidence for the potential of therapeutic antibody treatments in PAM.IMPORTANCENaegleria fowleri (N. fowleri) is a free-living amoeba that is found ubiquitously in warm freshwater. While human exposure is common, it rarely results in pathogenesis. However, when N. fowleri gains access to the upper airway, specifically the olfactory mucosa, infection leads to a lethal disease known as primary amoebic meningoencephalitis (PAM). As a free-living amoeba, N. fowleri does not need a mammalian host; indeed, it can be accurately described as an accidental opportunistic pathogen. While most opportunistic infections occur in humans who are immunocompromised, there are no reported immune dysfunctions associated with N. fowleri infection. Therefore, the basis for N. fowleri opportunism is not known, and the reasons why some humans develop PAM while others do not are simply not well understood. It is reasonable to speculate that local or acute immune failures, potentially even a lack of prior adaptive immunity, are related to disease susceptibility. Careful immune profiling and characterization of the in vivo immune response to N. fowleri in a mammalian host are desperately needed to understand which host factors are critical to defense, and how these responses might be compromised in a way that results in lethal infection. To identify genes and pathways that provide resistance against in vivo N. fowleri infection, we generated surface reactive monoclonal antibodies (Abs) that provide rapid amoeba detection and quantification in vivo. Interestingly, N. fowleri binding Abs have been readily detected in the serum and saliva of humans and animals suggesting that non-lethal exposure drives a humoral immune response against the amoeba. Yet, how Abs might interact with Naegleria in vivo or contribute to preventing lethal infection is not well understood. In this study, we have generated and characterized a monoclonal antibody (Ab), Clone 2B6, that recognizes a glycosylated surface antigen present in cultured in vitro N. fowleri as well as mouse passaged N. fowleri. When clone 2B6 binds to N. fowleri, it inhibits amoeba motility and feeding behavior, leading to strong growth inhibition. Mice treated systemically and intracerebrally with Ab displayed a delayed disease onset and prolonged survival. In addition, we found that enhancing immune-directed effector activity via antibody isotype could further enhance survival without obvious immunopathogenic side effects. These findings show the potential for antibody treatment as an additional therapeutic to those used currently in PAM.

Synthesis and Biological Evaluation of Cyanoacrylamides and 5-Iminopyrrol-2-Ones Against Naegleria fowleri

Primary amoebic meningoencephalitis is caused by the free-living amoeba Naegleria fowleri. The lack of standardized treatment has significantly contributed to the high fatality rates observed in reported cases. Therefore, this study aims to explore the anti-Naegleria activity of eight synthesized cyanoacrylamides and 5-iminopyrrol-2-ones. Notably, QOET-109, QOET-111, QOET-112, and QOET-114 exhibited a higher selectivity index against Naegleria compared to those of the rest of the compounds. Subsequently, these chemicals were assessed against the resistant stage of N. fowleri, demonstrating activity similar to that observed in the vegetative stage. Moreover, characteristic events of programmed cell death were evidenced, including chromatin condensation, increased plasma membrane permeability, mitochondrial damage, and heightened oxidative stress, among others. Finally, this research demonstrated the in vitro activity of the cyanoacrylamide and 5-iminopyrrol-2-one molecules, as well as the induction of metabolic event characteristics of regulated cell death in Naegleria fowleri.

Exploring the extrachromosomal plasmid rDNA of Naegleria fowleri AY27 genotype II: A human brain-eating amoeba via high-throughput sequencing

Naegleria fowleri, also known as brain-earing amoeba, causes severe and rapidly fatal CNS infection in humans called primary amebic meningoencephalitis (PAM). The DNA from the N. fowleri clinical isolate was sequenced for circular extrachromosomal ribosomal DNA (CERE - rDNA). The CERE contains 18 S, 5.8 S, and 28 S ribosomal subunits separated by internal transcribed spacers, 5 open reading frames (ORFs), and mostly repeat elements comprising 7268 bp out of 15,786 bp (46%). A wide variety of variations and recombination events were observed. Finally, the ORFs that comprised only 4 hypothetical proteins were modeled and screened against Zinc drug-like compounds. Two compounds [ZINC77564275 (ethyl 2-(((4-isopropyl-4 H-1,2,4-triazol-3-yl) methyl) (methyl)amino) oxazole-4-carboxylate) and ZINC15022129 (5-(2-methoxyphenoxy)-[2,2'-bipyrimidine]-4,6(1 H,5 H)-dione)] were finalized as potential druggable compounds based on ADME toxicity analysis. We propose that the compounds showing the least toxicity would be potential drug candidates after laboratory experimental validation is performed.

Contamination of fresh vegetables in municipal stores with pathogenic Acanthamoeba genotypes; a public health concern

Acanthamoeba spp. cause keratitis and encephalitis, and are a proper carrier of foodborne pathogens. A total of 70 samples including garden cress, chives, mint, parsley, and basil were collected. Samples were cultured onto a 2% non-nutrient agar medium. The cultures were analyzed using morphological and molecular techniques. In total, 18 (25.7%) out of 70 samples were positive including garden cress 10/22 (45.45%), chives 3/12 (25%), mint 2/13 (15.38%), basil 2/13 (15.38%), and parsley 1/10 (10%). The diagnostic fragment 3 was successfully sequenced in 15 samples and represented 11 (73.3%) T4, three (20%) T5, and one T9 genotypes. In addition, three, two, and one strains, belonging to the genotypes T4, T5, and T9 were ranked highly pathogenic. This is the first study reporting contamination of the most commonly consumed fresh vegetables with pathogenic Acanthamoeba genotypes. Our findings signify the public health concerns due the contamination of vegetables in municipal public markets.

Systematic Review of Brain-Eating Amoeba: A Decade Update

INTRODUCTION

Primary amoebic meningoencephalitis (PAM) is a rare but lethal infection of the brain caused by a eukaryote called Naegleria fowleri (N. fowleri). The aim of this review is to consolidate the recently published case reports of N. fowleri infection by describing its epidemiology and clinical features with the goal of ultimately disseminating this information to healthcare personnel.

METHODS

A comprehensive literature search was carried out using PubMed, Web of Science, Scopus, and OVID databases until 31 December 2022 by two independent reviewers. All studies from the year 2013 were extracted, and quality assessments were carried out meticulously prior to their inclusion in the final analysis.

RESULTS

A total of 21 studies were selected for qualitative analyses out of the 461 studies extracted. The cases were distributed globally, and 72.7% of the cases succumbed to mortality. The youngest case was an 11-day-old boy, while the eldest was a 75-year-old. Significant exposure to freshwater either from recreational activities or from a habit of irrigating the nostrils preceded onset. The symptoms at early presentation included fever, headache, and vomiting, while late sequalae showed neurological manifestation. An accurate diagnosis remains a challenge, as the symptoms mimic bacterial meningitis. Confirmatory tests include the direct visualisation of the amoeba or the use of the polymerase chain reaction method.

CONCLUSIONS

N. fowleri infection is rare but leads to PAM. Its occurrence is worldwide with a significant risk of fatality. The suggested probable case definition based on the findings is the acute onset of fever, headache, and vomiting with meningeal symptoms following exposure to freshwater within the previous 14 days. Continuous health promotion and health education activities for the public can help to improve knowledge and awareness prior to engagement in freshwater activities.

The Epidemiology and Clinical Features of Non-Keratitis Acanthamoeba Infections in the United States, 1956-2020

Background

Acanthamoeba is a free-living ameba that can cause severe disease affecting the central nervous system, skin, sinuses, and other organs, particularly in immunocompromised individuals. These rare but severe infections are often fatal, yet incompletely described.

Methods

Cases included were either reported to the Centers for Disease Control and Prevention (CDC) Free-Living Ameba program or published in scientific literature. Characteristics of all patients in the United States with laboratory-confirmed non-keratitis Acanthamoeba infections were described using descriptive statistics, and associations with survival were determined using χ² and Fisher exact tests.

Results

Of 173 patients identified, 71% were male and the median age was 44 years (range, 0-87 years). Of these, 26 (15%) survived. Most patients (88%) had at least 1 immunocompromising condition, most commonly human immunodeficiency virus (39%), cancer (28%), and solid organ or hematopoietic stem cell transplant (28%). Granulomatous amebic encephalitis (GAE) was the most common disease presentation (71%). Skin (46%), sinuses (29%), lungs (13%), and bone (6%) were also involved. Nearly half of patients (47%) had involvement of >1 organ system. Survival was less frequent among those with GAE (3%, P < .001) compared with cutaneous disease, rhinosinusitis, or multiorgan disease not including GAE. Of 7 who received the currently recommended treatment regimen, 5 (71%) survived.

Conclusions

Non-keratitis Acanthamoeba infections occur primarily in immunocompromised individuals and are usually fatal. Survival may be associated with disease presentation and treatment. Providers who care for at-risk patients should be aware of the various disease manifestations to improve early recognition and treatment.

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.

Case Report and Literature Review: Bacterial Meningoencephalitis or Not? Naegleria fowleri Related Primary Amoebic Meningoencephalitis in China

In China, a 9-year-old boy was transferred to the hospital with fever, vomiting, and headache. The disease rapidly deteriorated into vague consciousness. Applying conventional clinical examinations such as blood and cerebrospinal fluid (CSF) tests, the diagnosis of bacterial meningoencephalitis was first drawn, and expectant treatments were adopted immediately. However, the symptoms did not alleviate, adversely, this boy died 3 days after admission. Considering the skeptical points of the duration, such as the unknown infectious bacteria and the pathogen invasion path, blood and CSF samples were then sent for metagenomic next-generation sequencing (mNGS) to ascertain the cause of death. The 42,899 and 1,337 specific sequences of N. fowleri were detected by mNGS in the CSF sample and the blood sample, respectively. PCR results and pathological smear subsequently confirmed the mNGS detection. The patient was finally diagnosed as primary amoebic meningoencephalitis. Besides, in this article, 15 similar child infection cases in the past 10 years are summarized and analyzed to promote the early diagnosis of this rare disease.

Various brain-eating amoebae: the protozoa, the pathogenesis, and the disease

Among various genera of free-living amoebae prevalent in nature, some members are identified as causative agents of human encephalitis, in which Naegleria fowleri followed by Acanthamoeba spp. and Balamuthia mandrillaris have been successively discovered. As the three dominant genera responsible for infections, Acanthamoeba and Balamuthia work as opportunistic pathogens of granulomatous amoebic encephalitis in immunocompetent and immunocompromised individuals, whereas Naegleria induces primary amoebic meningoencephalitis mostly in healthy children and young adults as a more violent and deadly disease. Due to the lack of typical symptoms and laboratory findings, all these amoebic encephalitic diseases are difficult to diagnose. Considering that subsequent therapies are also affected, all these brain infections cause significant mortality worldwide, with more than 90% of the cases being fatal. Along with global warming and population explosion, expanding areas of human and amoebae activity in some regions lead to increased contact, resulting in more serious infections and drawing increased public attention. In this review, we summarize the present information of these pathogenic free-living amoebae, including their phylogeny, classification, biology, and ecology. The mechanisms of pathogenesis, immunology, pathophysiology, clinical manifestations, epidemiology, diagnosis, and therapies are also discussed.

Epidemiology and Clinical Characteristics of Primary Amebic Meningoencephalitis Caused by Naegleria fowleri: A Global Review

BACKGROUND

Primary amebic meningoencephalitis (PAM) is a rapidly progressive and often fatal condition caused by the free-living ameba Naegleria fowleri. To estimate the global occurrence, characterize the epidemiology, and describe the clinical features of PAM, we report a series of PAM cases published in the international literature and reported to the Centers for Disease Control and Prevention (CDC).

METHODS

We performed a literature search of PAM case reports published through 2018. Additionally, we included cases reported through the CDC's Free-Living Ameba surveillance or diagnosed via CDC's Free-Living and Intestinal Amebas Laboratory. Cases were classified as confirmed, probable, or suspect on the basis of confirmatory testing, presentation, exposure, and disease course.

RESULTS

A total of 381 PAM cases were identified. Seven reported survivors were classified as confirmed. The most commonly reported exposure associated with PAM was swimming/diving, and the most common class of water source was lakes/ponds/reservoirs. Patients were predominantly male (75%), with a median age of 14 years. Confirmed and probable cases were similar in their survival, course of illness, and cerebrospinal fluid (CSF) findings.

CONCLUSIONS

PAM is a rare but deadly disease with worldwide occurrence. Improved clinician awareness, resulting in earlier diagnosis and treatment, may contribute to increased survival among PAM patients. The case definition of probable used in this study appears to capture cases of PAM, as evidenced by similarities in outcomes, clinical course, and CSF profile to confirmed cases. In the absence of confirmatory testing, clinicians could use this case definition to identify cases of PAM.

Bazzocchi I, Bekhti K, E. Piñero J, Jiménez IA, Lorenzo-Morales J. Exploring the Anti-Infective Value of Inuloxin A Isolated from Inula viscosa against the Brain-Eating Amoeba (Naegleria fowleri) by Activation of Programmed Cell Death

Primary amoebic meningoencephalitis (PAM), caused by the pathogenic free-living amoeba Naegleria fowleri, is a rare but fatal disease. Nowadays, no fully effective therapy is available to erradicate or prevent this disease. Natural products could constitute a promising source of useful bioactive compounds in drug discovery. The present study is a characterization of main active compounds from the ethanolic extract of Inula viscosa (Asteraceae) leaves against N. fowleri trophozoites. Four compounds (1-4) were successfully identified by spectroscopic techniques, but only inuloxin A displayed a potential antiamoebic activity with an IC₅₀ of 21.27 μM. The specificity of this compound toward the studied strain leads us to analyze the insight into its mechanism of action by performing in vitro assays of programmed cell death markers and to discuss the structure-activity relationship (SAR). The obtained results demonstrated that inuloxin A interferes with various processes leading to membrane damage, mitochondria alteration, chromatin condensation, and ROS accumulation, which highlight features specific to apoptosis. The current findings could be a promising step for developing new effective drugs against PAM.

Understanding the true burden of "Naegleria fowleri" (Vahlkampfiidae) in patients from Northern states of India: Source tracking and significance

The present study is an attempt to investigate the presence of Naegleria fowleri in Indian population. A total of 307 patients were enrolled and water samples were collected from both residential and surrounding areas of patients found positive for N. fowleri. The different species of Naegleria from both clinical and water samples were identified taxonomically. Recommended microbiological conventional techniques were used to identify different Naegleria stages and other free-living amoebae from the samples. PCR assays, using both genus and species specific primers were also optimized. None of the samples were positive by conventional microbiological examinations. However, PCR assays detected only three samples positive for N. fowleri. A total of 10 water bodies (ponds), that were used by Naegleria positive patients were examined. The pH and temperature of the water samples collected from water bodies ranged between 5.6-7.2 and 25-32 °C respectively. Among all the 10 water samples tested, four samples were positive for genus Naegleria by PCR assay, of which only two samples, showed positive amplification for N. fowleri. The sequence analysis of N. fowleri strain belonged to genotype II.