Acute pyogenic meningitis probably due to Acanthamoeba sp.: a preliminary report

Advancing the understanding of Naegleria fowleri: Global epidemiology, phylogenetic analysis, and strategies to combat a deadly pathogen

Naegleria fowleri is a rare but deadly pathogen that has emerged as an important global public health concern. The pathogen induces primary amoebic meningoencephalitis (PAM), a rapidly progressive and almost always fatal life-threatening brain infection. The devastating impact of N. fowleri and the high mortality rate underscores a deeper understanding and the development of innovative strategies to tackle this issue. Despite various studies that have been conducted on N. fowleri, a comprehensive review that integrates recent findings and addresses critical gaps in understanding remains lacking. This review provides a detailed overview of N. fowleri epidemiology, transmission dynamics, phylogenetic diversity, state-of-the-art diagnostic techniques, therapeutic approaches, and preventive measures. We identified 488 PAM cases globally, reported since 1962, with the highest numbers in the US, Pakistan, and Australia. A phylogenetic analysis of 41 N. fowleri ITS-1, 5.8S, ITS-2 region-based sequences showed genotypic diversity, with genotypes II and III being the most prevalent in Asia, North America, and Europe. Effective approaches to preventing N. fowleri transmission include applying free chlorine to water in storage tanks, taking precautions while swimming, and performing ablution with sterilized water (e.g., boiled or distilled) while avoiding deep inhalation of water, especially in regions with high water contamination. This review highlights the global impact of N. fowleri, future surveillance strategies, prompt diagnosis, potential therapeutic options, and vaccine development to prevent PAM outbreaks. It highlights the importance of joint government and public health efforts to combat this deadly pathogen.

Identification of Naegleria fowleri antigens recognized by serum antibodies from people of Mexicali Valley, México

Naegleria fowleri is an amoeba that causes a fatal disease in the central nervous system known as primary amoebic meningoencephalitis (PAM) in humans. Most of the infections are acquired by people who practice recreational activities in water contaminated with trophozoites. Swimming and wading in irrigation channels of Mexicali are common practices for local people. Although there are some warning signposts in the surrounding sites, people continue using these channels for recreational purposes. In that region, cases of PAM have been reported; however, not everyone who comes into contact with contaminated water containing trophozoites becomes infected, and the factors influencing their immune response to N. fowleri remain unknown. We analyzed the levels of antibodies against N. fowleri in two groups: local individuals, including visitors who swam in the Mexicali channels, and a group from Mexico City (CDMX). In both groups, specific antibody responses were analyzed using immunoassays, including Western blot, ELISA, and cytochemistry. The highest levels of both IgG and IgA were found in samples from Mexicali, compared to those from CDMX. In both groups, IgG recognized polypeptide bands from N. fowleri at molecular weights of 100, 50, and 19 kDa, bands that we have already reported as immunogenic. Moreover, the IgG subjects recognized trophozoite structures such as membrane, pseudopodia, food cups, and even small like-vesicles. This antibody immune response directed against these polypeptide bands and trophozoite structures along with other factors could be participating in the defense of these people against PAM.

Cloning of nf-profilin and intercellular interaction with nf-actin in Naegleria fowleri cysts

Naegleria fowleri is a free-living amoeba found in lakes, soil, hot springs, and poorly chlorinated swimming pools. It is pathogenic to humans, causing a rare and fatal brain infection known as primary amoebic meningoencephalitis (PAM). A previous study utilized RNA-seq analysis to examine genes expressed in N. fowleri cysts and trophozoites, focusing on the nf-profilin gene, which showed high expression in cysts. Profilin is a small actin-binding protein that regulates nf-actin polymerization and cell movement. Sequence analysis revealed 83% similarity with non-pathogenic N. gruberi and 38% similarity with Acanthamoeba castellanii. Nf-profilin was found to be associated with N. fowleri lysates but not with lysates from other amoebae, as shown by Western blot analysis. Immunofluorescence assays demonstrated that nf-profilin primarily localized to the cell membrane in N. fowleri cysts, while nf-actin localized to the cytoplasm, pseudopodia, and food-cup structures. Real-time RT-PCR indicated higher expression of the nf-profilin gene in cysts compared to trophozoites. In co-culture experiments with target cells, Nf-profilin was initially expressed in the cytoplasm of N. fowleri cysts and the morphology of cyst gradually transitioned to the trophozoite form. Concurrently, the expression of Nf-profilin protein decreased, while Nf-actin protein began to appear in the pseudopodia and food-cups of trophozoites. In conclusion, the nf-profilin and nf-actin genes exhibited complementary expression patterns based on the life stage of N. fowleri, indicating their critical roles in the survival and proliferation. This study emphasizes the significance of actin-binding proteins in understanding the infection and pathogenic mechanisms of N. fowleri.

Free-living amoebae: a journey into historical aspects and to current discoveries

Free-living amoebas (FLA) are ubiquitous protists found in the environment. They have shown exceptional resistance to environmental challenges and play significant roles in controlling microbial populations through their predatory behaviour and microbicidal activity in both soil and aquatic ecosystems environments. However, although rare, a limited group of FLA can cause serious infections in the central nervous system and other diseases, particularly in immunocompromised individuals with high mortality rates. They can also cause keratitis in otherwise healthy individuals. This review offers a comprehensive overview of freshwater naked amoebae but does not cover all aspects in detail. Its goal is to provide a historical context for our current understanding while addressing the most critical elements of FLA biology, their pathogenic potential, and their interactions with important human pathogens.

Amoebas: the omnipotent organism and silent assassin

Amoebas are characterized by their unique ability to exist both as free-living organisms and, occasionally, as parasites within host tissues, earning them the designation 'amphizoic amoebae'. While amoebic infections are less prevalent, their health impact can be tremendous, leading to several diseases. In low-income countries, poor sanitation and socioeconomic conditions significantly increase the risk of amoebic infections, particularly E. histolytica, which affects up to 50 million people and causes over 100,000 deaths each year. Diagnostic methods, including microscopy, serological tests, polymerase chain reaction, and the loop-mediated isothermal amplification assay, have improved the accuracy and timeliness of amoeba diagnosis. However, these methodologies are often cost-prohibitive for developing countries. Conversely, current treatments involve aggressive protocols using antibiotics, antifungals, and anticancer agents. However, the prognosis for severe infections such as Primary Amoebic Meningoencephalitis and Granulomatous Amebic Encephalitis remains poor. Despite advancements, effective treatments, and new low-cost therapeutic options are still being researched. Thus, the current review sought to provide a description of molecular aspects such as amoeba virulence factors and invasion processes, focusing on recent advances in the detection, identification, and treatment of associated diseases.

Naegleria fowleri: Portrait of a Cerebral Killer

Background: Primary amebic meningoencephalitis (PAM) caused by Naegleria fowleri is a rare and devastating infection of the central nervous system, often diagnosed late, due to its rapid progression and nonspecific symptoms. Case Presentation: We report one of the youngest documented pediatric Vietnamese cases of PAM in a 10-month-old girl from the Mekong Delta, Vietnam. The diagnosis was confirmed through multiplex real-time PCR (MPL-rPCR), microscopy, and sequencing. Clinical data were gathered retrospectively from medical records, and additional details were provided by the patient's family. Treatment regimens, disease progression, and diagnostic challenges were reviewed and compared to existing literature. With intensive treatment, the child survived for 14 days, representing one of the longest reported pediatric PAM survival durations. No direct exposure to untreated freshwater or other typical risk factors for Naegleria fowleri infection was identified, underscoring the unique epidemiological nature of this case. MPL-rPCR enabled timely detection of the pathogen and demonstrated its utility in resource-limited settings. Conclusions: This case highlights the critical need for rapid, accessible diagnostic tools such as MPL-rPCR, particularly in resource-constrained environments where traditional diagnostics may not be feasible. It also emphasizes the importance of international collaboration and investment in cost-effective diagnostics and novel therapeutic strategies. The geographical expansion of PAM due to climate change further underscores the urgency of these measures to improve health outcomes in vulnerable populations.

Primary amebic meningoencephalitis: a review of Naegleria fowleri and analysis of successfully treated cases

Primary amebic meningoencephalitis (PAM) is a necrotizing and hemorrhagic inflammation of the brain and meninges caused by Naegleria fowleri, a free-living thermophilic ameba of freshwater systems. PAM remains a neglected disease that disproportionately affects children in tropical and subtropical climates, with an estimated mortality rate of 95-98%. Due to anthropogenic climate change, the average temperature in the USA has increased by 0.72 to 1.06 °C in the last century, promoting the poleward spread of N. fowleri. PAM is often misdiagnosed as bacterial meningitis or viral encephalitis, which shortens the window for potentially life-saving treatment. Diagnosis relies on the patient's history of freshwater exposure and the physician's high index of suspicion, supported by cerebrospinal fluid studies. While no experimental trials have been conducted to assess the relative efficacy of treatment regimens, anti-amebic therapy with adjunctive neuroprotection is standard treatment in the USA. We performed a literature review and identified five patients from North America between 1962 and 2022 who survived PAM with various degrees of sequelae.

Characterization of the extracellular vesicles, ultrastructural morphology, and intercellular interactions of multiple clinical isolates of the brain-eating amoeba, Naegleria fowleri

Introduction

As global temperatures rise to unprecedented historic levels, so too do the latitudes of habitable niches for the pathogenic free-living amoeba, Naegleria fowleri. This opportunistic parasite causes a rare, but >97% fatal, neurological infection called primary amoebic meningoencephalitis. Despite its lethality, this parasite remains one of the most neglected and understudied parasitic protozoans.

Methods

To better understand amoeboid intercellular communication, we elucidate the structure, proteome, and potential secretion mechanisms of amoeba-derived extracellular vesicles (EVs), which are membrane-bound communication apparatuses that relay messages and can be used as biomarkers for diagnostics in various diseases.

Results and Discussion

Herein we propose that N. fowleri secretes EVs in clusters from the plasma membrane, from multivesicular bodies, and via beading of thin filaments extruding from the membrane. Uptake assays demonstrate that EVs are taken up by other amoebae and mammalian cells, and we observed a real-time increase in metabolic activity for mammalian cells exposed to EVs from amoebae. Proteomic analysis revealed >2,000 proteins within the N. fowleri-secreted EVs, providing targets for the development of diagnostics or therapeutics. Our work expands the knowledge of intercellular interactions among these amoebae and subsequently deepens the understanding of the mechanistic basis of PAM.

Can Amphotericin B-mediated effects be limited using intranasal versus intravenous route?

Aim: CNS infections due to parasites often prove fatal. In part, this is due to inefficacy of drugs to cross the blood-brain barrier. Methods: Here, we tested intranasal and intravenous route and compared adverse effects of Amphotericin B administration, through blood biochemistry, liver, kidney and brain histopathological evidence of toxicities in vivo post-administration. Results: It was observed that intranasal route limits the adverse side effects of Amphotericin B, in contrast to intravenous route. Conclusion: As parasites such as Naegleria fowleri exhibit unequivocal affinity toward the olfactory bulb and frontal lobe in the central nervous system, intranasal administration would directly reach amoebae bypassing the blood-brain barrier selectivity and achieve the minimum inhibitory concentration at the target site.

First report of free-living amoebae in watercourses in southern Brazil: molecular diagnosis and phylogenetic analysis of Vermamoeba vermiformis, Naegleria gruberi, and Acanthamoeba spp

Free-living amoebae (FLA) are protozoa dispersed in different environments and are responsible for different infections caused to humans and other animals. Microorganisms such as Acanthamoeba spp., Vermamoeba sp., and Naegleria sp. are associated with diseases that affect the central nervous system, in addition to skin infections and keratitis, as occurs in the genus Acanthamoeba and with Vermamoeba vermiformis. Due to the concerns of these FLA in anthropogenic aquatic environments, this work aimed to identify these microorganisms present in waters of Porto Alegre, Brazil. One litre sample was collected in two watercourses during the summer of 2022 and inoculated onto non-nutrient agar plates containing heat-inactivated Escherichia coli. Polymerase chain reaction results indicated the presence of FLA of the genera Acanthamoeba, Vermamoeba, and Naegleria in the study areas. Genetic sequencing indicated the presence of V. vermiformis and Naegleria gruberi. These aquatic and anthropogenic environments can serve as a means of spread and contamination by FLA, which gives valuable information on public health in the city.

Genetic Detection of Amoebic Meningoencephalitis Causing by Naegleria Fowleri in Iraq: A Case Report

We diagnosed a case report of amoebic meningoencephalitis by Naegleria fowleri. This case represented the first recording in Iraq where it was not recording previously. This case was diagnosed after the death of an 18-year-old girl patient who lived in a rural area of Mosul in Iraq. Genetics detection of N. fowleri showed PCR product was 183bp for 18S rRNA gene. It was registered as the first recording of Iraqi isolate N. fowleri in GenBank with accession number OP380864.1. It is necessary to examine microscopically the cerebral spinal fluid (CSF) to observe the amoeba stages and exclude the bacterial causative. Rapid diagnosis may help in the treatment of amoebic meningoencephalitis. In addition, genetic identification can diagnose amoeba. Avoiding swimming or using freshwater contributes to prevent amoebic meningoencephalitis infection.

Identification and characterization of novel marine oxasqualenoid yucatecone against Naegleria fowleri

Naegleria fowleri is an opportunistic protozoan, belonging to the free-living amoeba group, that can be found in warm water bodies. It is causative agent the primary amoebic meningoencephalitis, a fulminant disease with a rapid progression that affects the central nervous system. However, no 100% effective treatments are available and those that are currently used involve the appearance of severe side effects, therefore, there is an urgent need to find novel antiamoebic compounds with low toxicity. In this study, the in vitro activity of six oxasqualenoids obtained from the red algae Laurencia viridis was evaluated against two different strains of N. fowleri (ATCC® 30808 and ATCC® 30215) as well as their cytotoxicity against murine macrophages. Yucatecone was the molecule with the highest selectivity index (>2.98 and 5.23 respectively) and it was selected to continue with the cell death type determination assays. Results showed that yucatone induced programmed cell death like responses in treated amoebae causing DNA condensation and cellular membrane damage among others. In this family of oxasqualenoids, it seems that the most significative structural feature to induce activity against N. fowleri is the presence of a ketone at C-18. This punctual oxidation transforms an inactive compound into a lead compound as the yucatecone and 18-ketodehydrotyrsiferol with IC₅₀ values of 16.25 and 12.70 μM, respectively. The assessment of in silico ADME/Tox analysis revealed that the active compounds showed good Human Oral Absorption and demonstrate that are found to be within the limit of approved drug parameter range. Hence, the study highlights promising potential of yucatone to be tested for therapeutic use against primary amoebic meningoencephalitis.

Identification of novel anti-amoebic pharmacophores from kinase inhibitor chemotypes

Acanthamoeba species, Naegleria fowleri, and Balamuthia mandrillaris are opportunistic pathogens that cause a range of brain, skin, eye, and disseminated diseases in humans and animals. These pathogenic free-living amoebae (pFLA) are commonly misdiagnosed and have sub-optimal treatment regimens which contribute to the extremely high mortality rates (>90%) when they infect the central nervous system. To address the unmet medical need for effective therapeutics, we screened kinase inhibitor chemotypes against three pFLA using phenotypic drug assays involving CellTiter-Glo 2.0. Herein, we report the activity of the compounds against the trophozoite stage of each of the three amoebae, ranging from nanomolar to low micromolar potency. The most potent compounds that were identified from this screening effort were: 2d (A. castellanii EC50: 0.92 ± 0.3 μM; and N. fowleri EC50: 0.43 ± 0.13 μM), 1c and 2b (N. fowleri EC50s: <0.63 μM, and 0.3 ± 0.21 μM), and 4b and 7b (B. mandrillaris EC50s: 1.0 ± 0.12 μM, and 1.4 ± 0.17 μM, respectively). With several of these pharmacophores already possessing blood-brain barrier (BBB) permeability properties, or are predicted to penetrate the BBB, these hits present novel starting points for optimization as future treatments for pFLA-caused diseases.

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.

In-silico drug design for the novel Karachi-NF001 strain of brain-eating amoeba: Naegleria fowleri

Naegleria fowleri (N. fowleri) is a free-living thermophilic amoeba of fresh water and soil. The amoeba primarily feeds on bacteria but can be transmitted to humans upon contact with freshwater sources. Furthermore, this brain-eating amoeba enters the human body through the nose and travels to the brain to cause primary amebic meningoencephalitis (PAM). N. fowleri has been reported globally since its discovery in 1961. Recently a new strain of N. fowleri named Karachi-NF001 was found in a patient who had traveled from Riyadh, Saudi Arabia to Karachi in 2019. There were 15 unique genes identified in the genome of the Karachi-NF001 strain compared to all the previously reported strains of N. fowleri worldwide. Six of these genes encode well-known proteins. In this study, we performed in-silico analysis on 5 of these 6 proteins, namely, Rab family small GTPase, NADH dehydrogenase subunit 11, two Glutamine-rich protein 2 proteins (locus tags: 12086 and 12110), and Tigger transposable element-derived protein 1. We conducted homology modeling of these 5 proteins followed by their active site identification. These proteins were subjected to molecular docking against 105 anti-bacterial ligand compounds as potential drugs. Subsequently, the 10 best-docked compounds were determined for each protein and ranked according to the number of interactions and their binding energies. The highest binding energy was recorded for the two Glutamine-rich protein 2 proteins with different locus tags, and results have shown that the protein-inhibitor complex was stable throughout the simulation run. Moreover, future in-vitro studies could validate the findings of our in-silico analysis and identify potential therapeutic drugs against N. fowleri infections.

Pro-inflammatory cytokine responses to Naegleria fowleri infection

Naegleria fowleri, or the “brain-eating amoeba,” is responsible for a rare, but lethal, infection known as primary amoebic meningoencephalitis (PAM). Confirmed PAM cases have seen both a rise in numbers, as well as expansion of geographic range over the past several decades. There is no effective therapy for PAM and the clinical prognosis remains grim with a mortality rate over 95%. The role of the immune response in disease prevention and disease severity remains unclear. In this review, we explore potential roles of inflammatory immune responses to N. fowleri in disease pathogenesis with a primary focus on pro-inflammatory cytokines IL-1, IL-6, and TNFα. We also discuss modulating proinflammatory cytokines as an additional immune therapy in PAM treatment.

Biological characteristics and pathogenicity of Acanthamoeba

Acanthamoeba is an opportunistic protozoa, which exists widely in nature and is mainly distributed in soil and water. Acanthamoeba usually exists in two forms, trophozoites and cysts. The trophozoite stage is one of growth and reproduction while the cyst stage is characterized by cellular quiescence, commonly resulting in human infection, and the lack of effective monotherapy after initial infection leads to chronic disease. Acanthamoeba can infect several human body tissues such as the skin, cornea, conjunctiva, respiratory tract, and reproductive tract, especially when the tissue barriers are damaged. Furthermore, serious infections can cause Acanthamoeba keratitis, granulomatous amoebic encephalitis, skin, and lung infections. With an increasing number of Acanthamoeba infections in recent years, the pathogenicity of Acanthamoeba is becoming more relevant to mainstream clinical care. This review article will describe the etiological characteristics of Acanthamoeba infection in detail from the aspects of biological characteristic, classification, disease, and pathogenic mechanism in order to provide scientific basis for the diagnosis, treatment, and prevention of Acanthamoeba infection.

Amebic infections of the central nervous system

The report of death of a person from amebic meningoencephalitis, the proverbial "brain-eating ameba," Naegleria fowleri, acquired in a state park lake in Iowa in July 2022 has once again raised the seasonal alarms about this pathogen. While exceptionally rare, its nearly universal fatality rate has panicked the public and made for good copy for the news media. This review will address free-living ameba that have been identified as causing CNS invasion in man, namely, Naegleria fowleri, Acanthamoeba species, Balamuthia mandrillaris, and Sappinia diploidea (Table 1). Of note, several Acanthamoeba spp. and Balamuthia mandrillaris may also be associated with localized extra-CNS infections in individuals who are immunocompetent and disseminated disease in immunocompromised hosts. These ameba are unique from other protozoa in that they are free-living, have no known insect vector, do not result in a human carrier state, and are typically unassociated with poor sanitation. Table 1 Free-living ameba that have been identified as causing CNS invasion in man, namely, Naegleria fowleri, Acanthamoeba species, Balamuthia mandrillaris, and Sappinia diploidea Entity Pathogenic ameba Predisposing disorders Portal of entry Incubation period Clinical features Radiographic findings CSF finding Diagnostic measures Primary amebic meningoencephalitis Naegleria fowleri; N. australiensis; N. italica Previously healthy children or young adults Olfactory epithelium 2-14 days (average 5 days) Headache, fever, altered mental status, meningeal signs; seizures Brain edema; meningeal enhancement; hydrocephalus; basal ganglia infarctions Increased opening pressure; neutrophilic pleocytosis (~ 1000 cells/cu mm); low glucose Brain biopsy, CSF wet prep, IIF culture or PCR Granulomatous amebic encephalitis Acanthamoeba spp.; Balamuthia mandrillaris; Sappinia diploidea Typically, immunocompromised individual Skin sinuses; olfactory epithelium respiratory tract Weeks to months Headache; altered mental status seizures, focal neurological findings Focal parenchymal lesions with edema; hemorrhagic infarctions; meningeal enhancement Generally, LP contraindicated; when performed lymphocytic pleocytosis; increased protein; low glucose Brain biopsy, CSF culture, wet prep, IIF, or PCR IIF indirect immunofluorescence, LP lumbar puncture, PCR polymerase chain reaction.

Prevalence of free-living amoebae in swimming pools and recreational waters, a systematic review and meta-analysis

Free-living amoebae (FLA) are cosmopolitan microorganisms known to be pathogenic to humans who often have a history of contact with contaminated water. Swimming pools and recreational waters are among the environments where the greatest human exposure to FLA occurs. This study aimed to determine the prevalence of FLA in swimming pools and recreational waters, through a systematic review and meta-analysis that included studies published between 1977 and 2022. A total of 106 studies were included and an overall prevalence of FLA in swimming pools and recreational waters of 44.34% (95% CI = 38.57–50.18) was found. Considering the studies published up to 2010 (1977–2010), between 2010 and 2015, and those published after 2010 (> 2010–2022), the prevalence was 53.09% (95% CI = 43.33–62.73) and 37.07% (95% CI = 28.87–45.66) and 45.40% (95% CI = 35.48–55.51), respectively. The highest prevalence was found in the American continent (63.99%), in Mexico (98.35%), and in indoor hot swimming pools (52.27%). The prevalence varied with the variation of FLA detection methods, morphology (57.21%), PCR (25.78%), and simultaneously morphology and PCR (43.16%). The global prevalence by genera was Vahlkampfia spp. (54.20%), Acanthamoeba spp. (33.47%), Naegleria spp. (30.95%), Hartmannella spp./Vermamoeba spp. (20.73%), Stenamoeba spp. (12.05%), and Vannella spp. (10.75%). There is considerable risk of FLA infection in swimming pools and recreational waters. Recreational water safety needs to be routinely monitored and, in case of risk, locations need to be identified with warning signs and users need to be educated. Swimming pools and artificial recreational water should be properly disinfected. Photolysis of NaOCl or NaCl in water by UV-C radiation is a promising alternative to disinfect swimming pools and artificial recreational waters.

Genotyping and Molecular Identification of Acanthamoeba Genotype T4 and Naegleria fowleri from Cerebrospinal Fluid Samples of Patients in Turkey: Is it the Pathogens of Unknown Causes of Death?

PURPOSE

This study was aimed to investigate the presence of pathogenic free-living amoebae (FLA) in suspected cases of meningoencephalitis with unknown causes of death in Turkey.

METHOD

A total of 92 patients, who were diagnosed as meningoencephalitis, were enrolled. All cerebrospinal fluid (CSF) samples were directly microscopically examined and cultured. Acanthamoeba, N. fowleri and B. mandrillaris were further investigated using molecular diagnostic tools including real-time PCR, sequencing, and phylogenetic analyses.

RESULTS

The examined CSF samples were not found positive for the presence of FLA by microscopic examination and culture method. However, two CSF samples were detected positive by real-time PCR assay. Of the positive CSF samples, one was identified as Acanthamoeba genotype T4 and the second positive sample was identified as N. fowleri belonging to genotype II. Furthermore, the pathogens diagnoses was verified through Sanger sequencing.

CONCLUSION

This study was significant to report the presence of Acanthamoeba genotype T4 and N. fowleri genotype II in CSF samples by real-time PCR assay. The present study shows the significance of primary amoebic meningoencephalitis (PAM) and granulomatous amoebic encephalitis (GAE) as one of the differential diagnoses to be considered by clinicians during the evaluation of suspected meningoencephalitis or cases of unknown cause in Turkey. Using real-time PCR, this has made the rapid detection, in a short time-frame, of Acanthamoeba and N. fowleri in CSF samples from patients. The problems with qPCR is that it is not available in every laboratory, reagents are expensive, and it requires skilled and expert personnel to set up these assays.

Polychlorinated cyclopentenes from a marine derived Periconia sp. (strain G1144)

Studies on an organic extract of a marine fungus, Periconia sp. (strain G1144), led to the isolation of three halogenated cyclopentenes along with the known and recently reported rhytidhyester D; a series of spectrometric and spectroscopic techniques were used to elucidate these structures. Interestingly, two of these compounds represent tri-halogenated cyclopentene derivatives, which have been observed only rarely from Nature. The relative and absolute configurations of the compounds were established via mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy, Mosher's esters method, optical rotation and GIAO NMR calculations, including correlation coefficient calculations and the use of both DP4+ and dJ DP4 analyses. Several of the isolated compounds were tested for activity in anti-parasitic, antimicrobial, quorum sensing inhibition, and cytotoxicity assays and were shown to be inactive.

Real-Time PCR Confirmation of a Fatal Case of Primary Amoebic Meningoencephalitis in Turkey Caused by Naegleria fowleri or Brain-Eating Amoeba

BACKGROUND

Naegleria fowleri, the causative agent of primary amoebic meningoencephalitis (PAM), is a free-living amoeba. It is a water-borne infection usually detected in children and young people with healthy immune system who swim, dive and perform activities in fresh and hot springs.

PURPOSE

In this study, it was aimed to raise awareness in the differential diagnosis of meningitis etiopathogenesis by showing that N. fowleri may also be the causative agent, albeit very rarely, in meningitis cases in Turkey.

METHODS

Our case was an 18-year-old male patient whose relatives stated that he has gone to the hot spring; his headache complaint started after 2 to 3 days after return from the hot spring. Cerebrospinal fluid (CSF) sample taken from the patient was investigated by direct microscopic examination, real-time PCR method and sequence analysis.

RESULTS

The CSF sample collected was taken into distilled water considering the possibility of transformation of trophozoites to intermediate form and incubated at 37 °C for 1 to 2 h, and pear-shaped non-permanent flagellated forms were observed in the direct microscopic examination, and molecular typing was performed to confirm the diagnosis. This study was a comprehensive case of N. fowleri whose etiological agent was isolated and confirmed by real-time PCR in Turkey.

CONCLUSION

Clinician awareness would be the key factor in correctly diagnosing PAM. It is also recommended to investigate all likely environmental water sources in Turkey for more detailed information on the distribution and molecular identification of Naegleria species, ultimately to evaluate the potential pathogenic threat to human health and to develop strategies to combat such threats.

Isolation of different parasites from the freshwater of Euphrates River in Anbar Province, Iraq

Intestinal parasites present in freshwater from the Al- Fallujah, Al- Habbaniyah and Al-Alwarar, of the Euphrates river in Iraq are Cryptosporidium spp (25.3%), Giardia sp (3.3%), Eimeria sp (3.3%), Pinworm eggs (3.3%), Naegleria sp (15.3%), Lecane niwati (1.3%), Trichomonas hominis (19.3%), Acanthamoeba spp (24.6%), Entamoeba coli (20.6%), Balantidium coli (12%), Ascaris sp (3.3%), Volvox sp (26%), Chilomastix mesnili (4%), Pelomyxa palustris (2.6%), Trinema enchelys (2.6%), Actinophrys Sol (7.3%), Amobea Vespertilio (9.3%), Rhabditea (5.3%), paramecium bursaria (9.3%), cyst of cestode (6%), Oocyst protozoa (16%), Euglena gracilis (10.6%).were isolated. The study's goal was to isolate some of the parasites that pollute the Euphrates water in Anbar Province and their impact on the health of living species and swimmers. Keywords. Acanthamoeba spp, Cryptosporidium, Fresh water, Giardia, Rotifer.

Cyclolauranes as plausible chemical scaffold against Naegleria fowleri

Primary amoebic meningoencephalitis (PAM) is a central nervous system (CNS) disease caused by Naegleria fowleri that mainly affects children and young adults with fatal consequences in most of the cases. Treatment protocols are based on the combination of different antimicrobial agents, nonetheless there is the need to develop new anti-Naegleria compounds with low toxicity and full effects compared to the currently used drug combination. The marine environment is a well-established source of bioactive natural products. In this work, we have focused on the structure of Laurencia cyclolaurane-type sesquiterpenes as potential chemical model against Naegleria species. The effects of debromolaurinterol (1) to induce PCD/apoptosis-like events in Naegleria fowleri have been evaluated, revealing that this compound induced reduction of ATP production showing a decrease of 99.98% in treated parasite cells. A SAR analysis have been supported with molecular modeling and analysis of the in silico ADME/Tox properties of the Laurencia sesquiterpenes debromolaurinterol (1), laurinterol (2) and allolaurinterol (3), which reinforce cyclolaurane metabolites as plausible molecular models to develop PAM treatments.

Case Report: First Successful Treatment of Acanthamoeba Brain Abscess with Combination Surgical Excision and Miltefosine-Led Antimicrobial Therapy

Acanthamoeba brain abscess is very rare and most often fatal. There remains no standardized regimen for its management. We report a case in northern Australia of an immunosuppressed 57-year-old man who presented with diarrhea and weight loss, and was diagnosed with multiple Acanthamoeba brain abscesses after neurological deterioration. This case is the first successful treatment with surgical excision followed by combination antimicrobial therapy including miltefosine. This case was treated initially as nocardiosis or melioidosis, emphasizing the importance of considering differentials such as Acanthamoeba during workup of atypical infection. We present a literature review of the 14 Acanthamoeba brain abscess cases reported in the English literature, of which five were successfully treated. Our review shows a predilection for multiple brain abscesses and an increased mortality rate compared with the general brain abscess population.

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.

The therapeutic potential of novel isobenzofuranones against Naegleria fowleri

The Free-Living Amoeba species, Naegleria fowleri is the causative agent of a lethal encephalitis known as Primary Amoebic Encephalitis (PAM). Moreover, most of the reported cases are often related to swimming and/or diving in aquatic environments. In addition, the current therapeutic options against PAM are not fully effective and hence, there is an urgent need to develop novel therapeutic agents against this disease. Previously isobenzofuranones compounds have been reported to present antiprotozoal and antifungal activity among others. However, to the best of our knowledge, these molecules have not been previously tested against N. fowleri. Therefore, the aim of this study was to evaluate the activity of 14 novel isobenzofuranones against this pathogenic amoeba. The most active and less toxic molecules, were assayed in order to check induction of Programmed Cell Death (PCD) in the treated amoebae. The obtained results showed that these molecules were able to eliminate N. fowleri trophozoites and also induced PCD. Therefore, the tested isobenzofuranones could be potential therapeutic candidates for the treatment of PAM.

Repurposing in vitro approaches for screening anti-parasitic drugs against the brain-eating amoeba Naegleria fowleri

Naegleria fowleri is both a pathogenic and a free-living microbial eukaryote, responsible for the development of primary amoebic meningoencephalitis (PAM) in humans. PAM is a rapid, severe and fatal underestimated infectious disease, which has been reported in countries with warmer climates. The major drawbacks with PAM are the lack of effective therapies and delay in diagnosis. The current frontline treatment presents a low rate of recovery (5%) and severe adverse effects. For example, many drug candidates lack efficacy, since they do not effectively cross the blood-brain-barrier. Consequently, more effective drugs are urgently needed. Herein, we report a new in vitro method suitable for medium- and high-throughput drug discovery assays, using the closely related Naegleria gruberi as a model. We have subsequently used this method to screen a library of 1175 Food and Drug Administration-approved drugs. As a result, we present three drugs (camptothecin, pyrimethamine, and terbinafine) that can be repurposed, and are anticipated to readily cross the blood-brain-barrier with activity against Naegleria species in therapeutically achievable concentrations. Successively, we integrated several in vitro assays that resulted in identifying fast-acting and high amoebicidal drugs. In conclusion, we present a new approach for the identification of anti-Naegleria drugs along with three potential drug candidates for further development for the treatment of PAM.

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.

Balamuthia mandrillaris: An opportunistic, free-living ameba - An updated review

Balamuthia mandrillaris is an opportunistic, free-living ameba that is pathogenic to humans. It has a worldwide distribution but is mainly detected in warmer regions. Balamuthia infections are rare but have been reported in both immunocompetent and immunocompromised individuals of all ages. B. mandrillaris can enter through wounds on the skin or the nose and cause cutaneous lesions and the usually fatal Balamuthia amebic encephalitis (BAE). Infection usually spreads from the lungs or through nerve fibers, and attacks the central nervous system, forming granulomatous lesions and necrosis in the brain. Balamuthia infection is usually chronic, and patients initially present with nonspecific symptoms, including headache, nausea, myalgia, and low-grade fever. As the disease progresses, the patient becomes paralyzed and comatose, often leading to death. Lack of knowledge of predisposing factors, specific treatment, and standardized detection tools have resulted in a nearly cent percent fatality rate. Although only about 200 cases have been reported worldwide since its characterization in the 1990s, the number of reported cases has increased over the years. BAE is an emerging disease and a major health concern. Few patients have survived Balamuthia infections with antimicrobial treatment that has largely been empirical. Early diagnosis is the key and requires familiarity with the disease and a high degree of suspicion on the part of the diagnostician. There are currently no specific treatment and prevention recommendations. This review highlights our current understanding of B. mandrillaris in terms of its pathogenicity, genomics, and novel diagnostic and therapeutic approaches against BAE infections.

Naphthyridine Derivatives Induce Programmed Cell Death in Naegleria fowleri

Primary amoebic encephalitis (PAM) caused by the opportunistic pathogen Naegleria fowleri is characterized as a rapid and lethal infection of the brain which ends in the death of the patient in more than 90% of the reported cases. This amoeba thrives in warm water bodies and causes infection after individuals perform risky activities such as splashing or diving, mostly in non-treated water bodies such as lakes and ponds. Moreover, the infection progresses very fast and no fully effective molecules have currently been found to treat PAM. In this study, naphthyridines fused with chromenes or chromenones previously synthetized by the group were tested in vitro against the trophozoite stage of two strains of N. fowleri. In addition, the most active molecule was evaluated in order to check the induction of programmed cell death (PCD) in the treated amoebae. Compound 3 showed good anti-Naegleria activity (61.45 ± 5.27 and 76.61 ± 10.84 µM, respectively) against the two different strains (ATCC^® 30808 and ATCC^® 30215) and a good selectivity compared to the cytotoxicity values (>300 µM). In addition, it was able to induce PCD, causing DNA condensation, damage at the cellular membrane, reduction in mitochondrial membrane potential and ATP levels, and ROS generation. Hence, naphthyridines fused with chromenes or chromenones could be potential therapeutic agents against PAM in the near future.

Current report on the prevalence of free-living amoebae (FLA) in natural hot springs: a systematic review

The occurrence of potentially pathogenic free-living amoebae (FLA) in natural hot springs is considered a public health concern. FLAs are known to cause serious health outcomes to a wide spectrum of mammalian hosts. The present study aimed to provide the distribution of isolated cases of FLAs in hot springs through a systematic review process of available published articles online. Relevant studies are published between January 2010 and January 2020 involving the isolation of Naegleria spp., Acanthamoeba spp., Balamuthia spp., Sappinia spp., and Vermamoeba spp. in natural hot springs in the United States, South America, North America, Europe, Asia, and Africa. Articles were identified through a search of PubMed and Google Scholar databases. Out of 94 articles screened, a total of 20 articles are included in the study with consideration of established inclusion and exclusion criteria. The most common FLAs isolated in hot springs are Acanthamoeba spp. (134; 48.5%) and Naegleria spp. (127; 46.0%). Other FLAs isolated in hot springs include Balamuthia spp. (2; 0.7%) and Vermamoeba spp. (13; 4.7%). FLA in hot springs used for recreational and medical purposes is a potential source of infection. It is recommended that strict surveillance and maintenance of hot springs be implemented to prevent potential future infection.

Revisiting the Mechanisms of Immune Evasion Employed by Human Parasites

For the establishment of a successful infection, i.e., long-term parasitism and a complete life cycle, parasites use various diverse mechanisms and factors, which they may be inherently bestowed with, or may acquire from the natural vector biting the host at the infection prelude, or may take over from the infecting host, to outmaneuver, evade, overcome, and/or suppress the host immunity, both innately and adaptively. This narrative review summarizes the up-to-date strategies exploited by a number of representative human parasites (protozoa and helminths) to counteract the target host immune defense. The revisited information should be useful for designing diagnostics and therapeutics as well as vaccines against the respective parasitic infections.

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.

EdU Incorporation To Assess Cell Proliferation and Drug Susceptibility in Naegleria fowleri

Naegleria fowleri is a pathogenic free-living amoeba that is commonly found in warm freshwater and can cause a rapidly fulminant disease known as primary amoebic meningoencephalitis (PAM). New drugs are urgently needed to treat PAM, as the fatality rate is >97%. Until recently, few advances have been made in the discovery of new drugs for N. fowleri, and one drawback is the lack of validated tools and methods to enhance drug discovery and diagnostics research. In this study, we aimed to validate alternative methods to assess cell proliferation that are commonly used for other cell types and develop a novel drug screening assay to evaluate drug efficacy on N. fowleri replication. EdU (5-ethynyl-2'-deoxyuridine) is a pyrimidine analog of thymidine that can be used as a quantitative endpoint for cell proliferation. EdU incorporation is detected via a copper catalyzed click reaction with an Alexa Fluor-linked azide. EdU incorporation in replicating N. fowleri was validated using fluorescence microscopy, and quantitative methods for assessing EdU incorporation were developed by using an imaging flow cytometer. Currently used PAM therapeutics inhibited N. fowleri replication and EdU incorporation in vitro. EdA (7-deaza-2'-deoxy-7-ethynyladenosine), an adenine analog, also was incorporated by N. fowleri but was more cytotoxic than EdU. In summary, EdU incorporation could be used as a complimentary method for drug discovery for these neglected pathogens.

Case Report: Encephalitis Caused by Balamuthia mandrillaris in a 3-Year-Old Iranian Girl

It is about half a century since free-living amoebae were recognized as pathogenic organisms, but there is still much we should learn about these rare fatal human infectious agents. A recently introduced causative agent of granulomatous amoebic encephalitis, Balamuthia mandrillaris, has been reported in a limited number of countries around the world. A 3-year-old girl was referred to our tertiary hospital because of inability to establish a proper diagnosis. She had been experiencing neurologic complaints including ataxia, altered level of consciousness, dizziness, seizure, and left-sided hemiparesis. The patient's history, physical examination results, and laboratory investigations had led to a wide differential diagnosis. Computed tomography (CT) scan and magnetic resonance imaging analyses revealed multiple mass lesions. As a result, the patient underwent an intraoperative frozen section biopsy of the brain lesion. The frozen section study showed numerous cells with amoeba-like appearances in the background of mixed inflammatory cells. Medications for free-living amoebic meningoencephalitis were administered. PCR assay demonstrated B. mandrillaris as the pathogenic amoeba. Unfortunately, the patient died 14 days after her admission. To our knowledge, this is the first report of B. mandrillaris meningoencephalitis in the Middle East and the first time we have captured the organism during a frozen-section study.

Potential Application of Vaporized Drugs via Nasal Inhalers to Prevent Mortality and Central Nervous System Damage Caused by Primary Amoebic Meningoencephalitis Due to Naegleria fowleri

Here, it is proposed that nasal inhalers with specific anti-Naegleria fowleri drugs or a combination of anti-N. fowleri compounds combined with steroids such as dexamethasone could provide a practical solution for treating primary amoebic meningoencephalitis.

The type 2 statins, cerivastatin, rosuvastatin and pitavastatin eliminate Naegleria fowleri at low concentrations and by induction of programmed cell death (PCD)

Primary Amoebic Encephalitis due to Naegleria fowleri species is a fatal infection of the Central Nervous System mostly affecting children and young adults. Infections often occur after performance of risk activities in aquatic habitats such as swimming and splashing. PAḾs therapy remain a key issue to be solved which needs an urgent development. Recently, statins have been highlighted as possible novel compounds to treat PAM. Furthermore, type 2 statins due to improved pharmacological properties and lower toxicity could be use in the future. In the present work, three type 2 statins were checked for their activity against two type strains of N. fowleri. In addition, the effects at the cellular level triggered in treated amoebae were checked in order to evaluate if programmed cell death was induced. The obtained results showed that the tested statins, rosuvastatin, pitavastatin and cerivastatin were able to eliminate N. fowleri trophozoites and also induced PCD. Therefore, type 2 statins could be used in the near future for the treatment of PAM.

A Search for Anti-Naegleria fowleri Agents Based on Competitive Exclusion Behavior of Microorganisms in Natural Aquatic Environments

Naegleria fowleri causes deadly primary amoebic meningoencephalitis (PAM) in humans. Humans obtain the infection by inhaling water or dust contaminated with amebae into the nostrils, wherefrom the pathogen migrates via the olfactory nerve to cause brain inflammation and necrosis. Current PAM treatment is ineffective and toxic. Seeking new effective and less toxic drugs for the environmental control of the amoeba population to reduce human exposure is logical for the management of N. fowleri infection. On the basis of the concept of competitive exclusion, where environmental microorganisms compete for resources by secreting factors detrimental to other organisms, we tested cell-free culture supernatants (CFSs) of three bacteria isolated from a fresh water canal, i.e., Pseudomonas aeruginosa, Pseudomonas otitidis, and Enterobacter cloacae, were tested against N. fowleri. The CFSs inhibited growth and caused morphological changes in N. fowleri. At low dose, N. fowleri trophozoites exposed to P. aeruginosa pyocyanin were seen to shrink and become rounded, while at high dose, the trophozoites were fragmented. While the precise molecular mechanisms of pyocyanin and products of P. otitidis and E. cloacae that also exert anti-N. fowleri activity await clarification. Our findings suggest that P. aeruginosa pyocyanin may have a role in the control of amphizoic N. fowleri in the environment.

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.

Complete Genome Sequence of the Naegleria fowleri (Strain LEE) Closed Circular Extrachromosomal Ribosomal DNA Element

The circular extrachromosomal ribosomal DNA (rDNA) element of Naegleria fowleri strain LEE was molecularly cloned and fully sequenced. The element comprises 15,786 bp and encodes a single copy of the organism’s rDNA cistron. The nonribosomal sequence contains five potential open reading frames, two large direct repeat sequences, and numerous smaller repeated-sequence regions.

The circular extrachromosomal ribosomal DNA (rDNA) element of Naegleria fowleri strain LEE was molecularly cloned and fully sequenced. The element comprises 15,786 bp and contains a single copy of the organism’s rDNA cistron. The nonribosomal sequence contains five potential open reading frames, two large direct repeat sequences, and numerous smaller repeated-sequence regions.

Laurinterol from Laurencia johnstonii eliminates Naegleria fowleri triggering PCD by inhibition of ATPases

Primary amoebic encephalitis (PAM) is a lethal disease caused by the opportunistic pathogen, Naegleria fowleri. This amoebic species is able to live freely in warm aquatic habitats and to infect children and young adults when they perform risk activities in these water bodies such as swimming or splashing. Besides the need to increase awareness of PAM which will allow an early diagnosis, the development of fully effective therapeutic agents is needed. Current treatment options are amphotericin B and miltefosine which are not fully effective and also present toxicity issues. In this study, the in vitro activity of various sesquiterpenes isolated from the red alga Laurencia johnstonii were tested against the trophozoite stage of a strain of Naegleria fowleri. Moreover, the induced effects (apoptotic cell death) of the most active compound, laurinterol (1), was evaluated by measuring DNA condensation, damages at the mitochondrial level, cell membrane disruption and production of reactive oxygen species (ROS). The obtained results demonstrated that laurinterol was able to eliminate the amoebae at concentrations of 13.42 ± 2.57 µM and also to induced programmed cell death (PCD) in the treated amoebae. Moreover, since ATP levels were highly affected and laurinterol has been previously reported as an inhibitor of the Na⁺/K⁺-ATPase sodium–potassium ion pump, comparison with known inhibitors of ATPases were carried out. Our results points out that laurinterol was able to inhibit ENA ATPase pump at concentrations 100 times lower than furosemide.

Isolation and Identification of Naegleria Species in Irrigation Channels for Recreational Use in Mexicali Valley, Mexico

Members of the genus Naegleria are free-living amoebae that are widely distributed in water and soil environments. Moreover, Naegleria fowleri is a pathogenic amoeba species that causes a fatal disease in the central nervous system known as primary amoebic meningoencephalitis (PAM) in humans. Since most reported infections due to N. fowleri are reported in recreational waters worldwide, this study was aimed to describe the presence of these amoebic genus in Mexicali Valley irrigation channels of recreational use. A total of nine water samples were collected and processed by triplicate, in nine different sites of the Valley. After filtering and culturing the samples, plates were examined, and the observed amoebae were morphologically identified at the genus level. In addition, the pathogenicity of these amoebic isolates was checked, and molecular characterization was performed by PCR/sequencing. The results revealed the presence of Naegleria spp. in all the channels sampled. Finally, molecular identification confirmed the presence of five different species of Naegleria: N. fowleri, N. australiensis, N. gruberi, N. clarki and N. pagei. The presence of these protists, particularly N. fowleri, should be considered as a potential human health risk in the region.

Discovery of repurposing drug candidates for the treatment of diseases caused by pathogenic free-living amoebae

Diseases caused by pathogenic free-living amoebae include primary amoebic meningoencephalitis (Naegleria fowleri), granulomatous amoebic encephalitis (Acanthamoeba spp.), Acanthamoeba keratitis, and Balamuthia amoebic encephalitis (Balamuthia mandrillaris). Each of these are difficult to treat and have high morbidity and mortality rates due to lack of effective therapeutics. Since repurposing drugs is an ideal strategy for orphan diseases, we conducted a high throughput phenotypic screen of 12,000 compounds from the Calibr ReFRAME library. We discovered a total of 58 potent inhibitors (IC50 <1 μM) against N. fowleri (n = 19), A. castellanii (n = 12), and B. mandrillaris (n = 27) plus an additional 90 micromolar inhibitors. Of these, 113 inhibitors have never been reported to have activity against Naegleria, Acanthamoeba or Balamuthia. Rapid onset of action is important for new anti-amoeba drugs and we identified 19 compounds that inhibit N. fowleri in vitro within 24 hours (halofuginone, NVP-HSP990, fumagillin, bardoxolone, belaronib, and BPH-942, solithromycin, nitracrine, quisinostat, pabinostat, pracinostat, dacinostat, fimepinostat, sanguinarium, radicicol, acriflavine, REP3132, BC-3205 and PF-4287881). These compounds inhibit N. fowleri in vitro faster than any of the drugs currently used for chemotherapy. The results of these studies demonstrate the utility of phenotypic screens for discovery of new drugs for pathogenic free-living amoebae, including Acanthamoeba for the first time. Given that many of the repurposed drugs have known mechanisms of action, these compounds can be used to validate new targets for structure-based drug design.

Balamuthia mandrillaris encephalitis in a child: case report and literature review

Balamuthia mandrillaris encephalitis is a rare disease with high mortality in the children. Due to the lack of specificity in clinical manifestations, laboratory tests, and neuroimaging, the diagnosis of the disease is difficult, especially the diagnosis of etiology. Currently, the evidence shows that the diagnosis of the disease depends on local brain biopsy or autopsy, and it is difficult to detect the pathogens by traditional etiological detection methods in blood and cerebrospinal fluid. We report a 9-year-old Chinese girl with B. mandrillaris encephalitis who was diagnosed with metagenomic next-generation sequencing (mNGS). The technology of mNGS can provide rapid, early etiological diagnosis without the need for a local brain biopsy, which can buy time for the early treatment of patients. We also provide a comprehensive literature review on this disease.

A Fatal Case of Primary Amoebic Meningoencephalitis (PAM) Complicated with Diabetes Insipidus (DI): A Case Report and Review of the Literature

Naegleria fowleri is a highly infective free-living amoeba usually isolated from soil and fresh water and is primarily found to infect the central nervous system (CNS) resulting in primary amoebic meningoencephalitis (PAM). PAM as a cause of meningitis is often overlooked for other, more common causes of meningitis. Despite all the advances in antimicrobial therapy and supportive care systems, the mortality rate of this rare infection remains above 95% with the bulk of the cases being found in developed countries. We are presenting a case of a 44-year-old male with fever, worsening headache, and generalized weakness. Lumbar puncture showed a raised leucocyte count of 1100/µL with predominant polymorphonuclear cells, and wet mount prep for Naegleria fowleri was positive further confirmed with PCR. The patient was started Intravenous (IV) and intrathecal amphotericin-B, Per Oral (PO) miltefosine, IV rifampin, IV fluconazole, and IV dexamethasone. However, the patient started producing urine at 300–500 ml/hour. The patient's sodium levels increased from 144 to 175 mmol/L in 12 hours with raised serum osmolality and decreased urine osmolality and urine sodium. The patient was started on PO desmopressin of 0.2 micrograms twice daily after which his urine output dropped to 60–80 ml/hour and sodium decreased from 175 to 162 and, later 155 mmol/L; however, the patient expired. PAM is a rare and extremely fatal illness, but with increasing incidence now being reported in developing countries as a result of better diagnostics. DI is a very rare complication reported in these patients leading to poor outcome. The complication of diabetes insipidus (DI) has not been extensively studied in patients having PAM. Only three cases have been reported with this complication. No mechanism has been mentioned in the literature behind the development of DI in these patients, and no study has mentioned laboratory details of DI as mentioned in this report.

Primary amebic meningoencephalomyelitis caused by Naegleria fowleri in a south-central black rhinoceros (Diceros bicornis minor)

CASE DESCRIPTION A 20-year-old female south-central black rhinoceros (Diceros bicornis minor) was evaluated because of an acute onset of CNS deficits. CLINICAL FINDINGS The rhinoceros had no history of illness. Clinical signs included acute lethargy, ataxia, and decreased appetite. Hematologic abnormalities included leukocytosis with neutrophilia and a profound left shift. Results of serum biochemical analysis revealed hypophosphatemia but no other abnormalities. Results of a quantitative PCR assay for West Nile virus and an assay for anti-Neosporum caninum antibodies in serum were negative; the patient was seropositive for multiple Leptospira serovars. TREATMENT AND OUTCOME Antimicrobials and anti-inflammatory agents were administered, but the condition of the rhinoceros worsened overnight; despite treatment with additional anti-inflammatory and antimicrobial agents, IV fluids, and thiamine, it became obtunded and died of respiratory arrest ≤ 24 hours later. Necropsy revealed severe, diffuse, suppurative, and histiocytic meningo-encephalomyelitis involving the cerebrum, cerebellum, and spinal cord. Amebic trophozoites were observed on histologic examination of affected tissue. Infection with Naegleria fowleri was confirmed by results of immuno-histochemical analysis and a multiplex real-time PCR assay. CLINICAL RELEVANCE Findings suggested that south-central black rhinoceros are susceptible to the free-living ameba N fowleri. Ameba-induced meningoencephalomyelitis should be considered as a differential diagnosis for rhinoceros that have an acute onset of neurologic signs. Diagnosis of N fowleri infection in an animal has a profound public health impact because of potential human exposure from the environment and the high fatality rate in people with N fowleri infection.