Infections with free-living amebae

Free-living amoebic encephalitis - Case series

Introduction

Free-living amoeba is ubiquitous in fresh water, mud, and moist soil; although seldom pathogenic to humans, Naegleria fowleri, Acanthamoeba spp., and Balamuthia spp. are known to cause infections of the central nervous system.

Methods

We report two interesting cases, both of which presented with a rapid-onset and fulminant course. The first case details a 36-year-old male with a history of surgically corrected nasal bone fracture 15 years back, who presented with acute onset of fever, headache and convulsions.

Results

Direct smears of cerebrospinal fluid (CSF) revealed motile trophozoites resembling N. fowleri and were later confirmed by molecular diagnosis (polymerase chain reaction [PCR]). Subsequently, the source was identified as water used for religious purposes. Unfortunately, the patient succumbed to cardiac arrest. The second case is that of a 4-year-old boy from Palakkad district, Kerala, who presented with sudden onset of nasal discharge, fever, headache, vomiting, seizures and altered sensorium. His CSF smear examination showed motile trophozoites resembling Acanthamoeba spp. While undergoing treatment, he seized thrice before going into cardiac arrest. Despite extensive resuscitation measures, the child could not be revived and passed away. The postmortem CSF sample sent for molecular analysis confirmed infection by Acanthamoeba spp.

Conclusion

Rapid progression and lack of definite treatment options make this a highly fatal condition. Although clinical presentations of both patients were indicative of pyogenic meningitis, parasitic infection was suspected when the CSF was found turbid with no bacteria, high protein, and low sugar. High index of suspicion helped us to get an early preliminary diagnosis from direct microscopy.

Azole-based compounds as potential anti-Acanthamoeba agents

Acanthamoeba castellanii is an opportunistic pathogen with public health implications, largely due to its invasive nature and non-specific symptoms. Our study focuses on the potential of azole compounds, particularly those with triazole scaffolds, as anti-amoebic agents. Out of 10 compounds, compounds T1 and T8 exhibited effective anti-Acanthamoeba activity with MIC50 values of 125.37 and 143.92 μg mL-1, respectively. Interestingly, compounds T1, T4, T5 and T8 revealed profound anti-excystation activity with MIC50 at 32.01, 85.53, 19.54 and 80.57 μg mL-1, respectively, alongside limited cytotoxicity to human cells. The study underscores the potential of T1, T4, T5, and T8, thiazole-based compounds, as anti-Acanthamoeba agents by both eliminating amoeba viability and preventing excystation, via preserving the amoeba in its latent cyst form, exposing them to elimination by the immune system. Notably, compounds T1, T4, T5, and T8 showed optimal molecular properties, moderate oral bioavailability, and stable complex formation with Acanthamoeba CYP51. They also display superior binding interactions. Further research is needed to understand their mechanisms and optimize their efficacy against Acanthamoeba infections.

Amoebicidal effect of chlorine dioxide gas against pathogenic Naegleria fowleri and Acanthamoeba polyphaga

The pathogenic free-living amoebae, Naegleria fowleri and Acanthamoeba polyphaga, are found in freshwater, soil, and unchlorinated or minimally chlorinated swimming pools. N. fowleri and A. polyphaga are becoming problematic as water leisure activities and drinking water are sources of infection. Chlorine dioxide (ClO2) gas is a potent disinfectant that is relatively harmless to humans at the concentration used for disinfection. In this study, we examined the amoebicidal effects of ClO2 gas on N. fowleri and A. polyphaga. These amoebae were exposed to ClO2 gas from a ready-to-use product (0.36 ppmv/h) for 12, 24, 36, and 48 h. Microscopic examination showed that the viability of N. fowleri and A. polyphaga was effectively inhibited by treatment with ClO2 gas in a time-dependent manner. The growth of N. fowleri and A. polyphaga exposed to ClO2 gas for 36 h was completely inhibited. In both cases, the mRNA levels of their respective actin genes were significantly reduced following treatment with ClO2 gas. ClO2 gas has an amoebicidal effect on N. fowleri and A. polyphaga. Therefore, ClO2 gas has been proposed as an effective agent for the prevention and control of pathogenic free-living amoeba contamination.

Nanoparticle-Terpene Fusion: A Game-Changer in Combating Primary Amoebic Meningoencephalitis Caused by Naegleria fowleri

Pathogenic Naegleria fowleri (N. fowleri) are opportunistic free-living amoebae and are the causative agents of a very rare but severe brain infection called primary amoebic meningoencephalitis (PAM). The fatality rate of PAM in reported cases is more than 95%. Most of the drugs used againstN. fowleri infections are repurposed drugs. Therefore, a large number of compounds have been tested againstN. fowleri in vitro, but most of the tested compounds showed high toxicity and an inability to cross the blood-brain barrier. Andrographolide, forskolin, and borneol are important natural compounds that have shown various valuable biological properties. In the present study, the nanoconjugates (AND-AgNPs, BOR-AgNPs, and FOR-AgNPs) of these compounds were synthesized and assessed against both stages (trophozoite and cyst) ofN. fowleri for their antiamoebic and cysticidal potential in vitro. In addition, cytotoxicity and host cell pathogenicity were also evaluated in vitro. FOR-AgNPs were the most potent nanoconjugate and showed potent antiamoebic activity againstN. fowleriwith an IC50 of 26.35 μM. Nanoconjugates FOR-AgNPs, BOR-AgNPs, and AND-AgNPs also significantly inhibit the viability of N. fowleri cysts. Cytotoxicity assessment showed that these nanoconjugates caused minimum damage to human keratinocyte cells (HaCaT cells) at 100 μg/mL, while also effectively reducing the cytopathogenicity of N. fowleri trophozoites to the HaCaT cells. The outcomes of our experiments have unveiled substantial potential for AND-AgNPs, BOR-AgNPs, and FOR-AgNPs in the realm of developing innovative alternative therapeutic agents to combat infections caused by N. fowleri. This study represents a significant step forward in the pursuit of advanced strategies for managing such amoebic infections, laying the foundation for the development of novel and more effective therapeutic modalities in the fight against free-living amoebae.

Miconazole-like Scaffold is a Promising Lead for Naegleria fowleri-Specific CYP51 Inhibitors

Developing drugs for brain infection by Naegleria fowleri is an unmet medical need. We used a combination of cheminformatics, target-, and phenotypic-based drug discovery methods to identify inhibitors that target an essential N. fowleri enzyme, sterol 14-demethylase (NfCYP51). A total of 124 compounds preselected in silico were tested against N. fowleri. Nine primary hits with EC50 ≤ 10 μM were phenotypically identified. Cocrystallization with NfCYP51 focused attention on one primary hit, miconazole-like compound 2a. The S-enantiomer of 2a produced a 1.74 Å cocrystal structure. A set of analogues was then synthesized and evaluated to confirm the superiority of the S-configuration over the R-configuration and the advantage of an ether linkage over an ester linkage. The two compounds, S-8b and S-9b, had an improved EC50 and KD compared to 2a. Importantly, both were readily taken up into the brain. The brain-to-plasma distribution coefficient of S-9b was 1.02 ± 0.12, suggesting further evaluation as a lead for primary amoebic meningoencephalitis.

Natural Terpenes Inhibit the Cytopathogenicity of Naegleria fowleri Causing Primary Amoebic Meningoencephalitis in the Human Cell Line Model

Naegleria fowleri is one of the free-living amoebae and is a causative agent of a lethal and rare central nervous system infection called primary amoebic meningoencephalitis. Despite the advancement in antimicrobial chemotherapy, the fatality rate in the reported cases is more than 95%. Most of the treatment drugs used against N. fowleri infection are repurposed drugs. Therefore, a large number of compounds have been tested against N. fowleri in vitro, but most of the compounds showed high toxicity. To overcome this, we evaluated the effectiveness of naturally occurring terpene compounds against N. fowleri. In this study, we evaluated the antiamoebic potential of natural compounds including Thymol, Borneol, Andrographolide, and Forskolin againstN. fowleri. Thymol showed the highest amoebicidal activity with IC50/24 h at 153.601 ± 19.6 μM. Two combinations of compounds Forskolin + Thymol and Forskolin + Borneol showed a higher effect on the viability of trophozoites as compared to compounds alone and hence showed a synergistic effect. The IC50 reported for Forskolin + Thymol was 81.30 ± 6.86 μM. Borneol showed maximum cysticidal activity with IC50/24 h at 192.605 ± 3.01 μM. Importantly, lactate dehydrogenase release testing revealed that all compounds displayed minimal cytotoxicity to human HaCaT, HeLa, and SH-SY5Y cell lines. The cytopathogenicity assay showed that Thymol and Borneol also significantly reduced the host cell cytotoxicity of pretreated amoeba toward the human HaCaT cell line. So, these terpene compounds hold potential as therapeutic agents against infections caused by N. fowleri and are potentially a step forward in drug development against this deadly pathogen as these compounds have also been reported to cross the blood-brain barrier. Therefore, an in vivo study using animal models is necessary to assess the efficacy of these compounds and the need for further research into the intranasal route of delivery for the treatment of these life-threatening infections.

Saline-Tolerant Pathogenic Acanthamoeba spp. Isolated from a Geothermal Power Plant

Few studies have been conducted in the cooling systems of power plants; they have focused on Naegleria fowleri, leaving a gap in the knowledge of other pathogenic free-living amoebae in this environment. The objective of this study was to determine the occurrence of saline-tolerant pathogenic Acanthamoeba in a geothermal power plant. The identification of isolated amoebae at genus level was carried out, observing their morphological characteristics; the determination of genotype and species of Acanthamoeba was performed via molecular biology (PCR). Water temperature ranged from 18 to 43 °C and conductivity from 4.0 × 104 to 8.7 × 104 μS/cm; this last value was greater than the seawater value. Only five amoeba genera were found. Acanthamoeba was in all the sampling sites, showing high saline tolerance. The high temperature, but mainly high conductivity, were the environmental conditions that determined the presence of pathogenic free-living amoebae in the hot water. All the strains of Acanthamoeba culbertsoni killed the mice, having a mortality of 40 to 100%. Acanthamoeba genotypes T10 and T5 were identified, T10 is rarely isolated from the environment, while T5 is more frequent. This is the first time that genotypes T5 and T10 have been reported in the environment in Mexico.

The global epidemiology and clinical diagnosis of Acanthamoeba keratitis

Acanthamoeba keratitis is a rare parasitic infection of the cornea that can lead to permanent blindness if not diagnosed and treated promptly. We collected data on the incidences of Acanthamoeba keratitis from 20 countries and calculated an annual incidence of 23,561 cases, with the lowest rates in Tunisia and Belgium, and the highest in India. We analyzed 3755 Acanthamoeba sequences from the GenBank database across Asia, Europe, North America, South America, and Oceania and genotyped them into T1, T2, T3, T4, T5, T10, T11, T12, and T15. Many genotypes possess different characteristics, yet T4 is the most prevalent genotype. As efficient treatment against Acanthamoeba remains lacking, prevention from early diagnosis via staining, PCR, or in vivo confocal microscopy (IVCM) becomes significant for the condition's prognosis. IVCM is the most recommended approach for the early detection of Acanthamoeba. If IVCM is unavailable, PCR should be used as an alternative.

Acanthamoeba castellanii Genotype T4: Inhibition of Proteases Activity and Cytopathic Effect by Bovine Apo-Lactoferrin

Acanthamoeba castellanii genotype T4 is a clinically significant free-living amoeba that causes granulomatous amoebic encephalitis and amoebic keratitis in human beings. During the initial stages of infection, trophozoites interact with various host immune responses, such as lactoferrin (Lf), in the corneal epithelium, nasal mucosa, and blood. Lf plays an important role in the elimination of pathogenic microorganisms, and evasion of the innate immune response is crucial in the colonization process. In this study, we describe the resistance of A. castellanii to the microbicidal effect of bovine apo-lactoferrin (apo-bLf) at different concentrations (25, 50, 100, and 500 µM). Acanthamoeba castellanii trophozoites incubated with apo-bLf at 500 µM for 12 h maintained 98% viability. Interestingly, despite this lack of effect on viability, our results showed that the apo-bLf inhibited the cytopathic effect of A. castellanii in MDCK cells culture, and analysis of amoebic proteases by zymography showed significant inhibition of cysteine and serine proteases by interaction with the apo-bLf. From these results, we conclude that bovine apo-Lf influences the activity of A. castellanii secretion proteases, which in turn decreases amoebic cytopathic activity.

Dual-Mode Gold Nanoparticle-Based Method for Early Detection of Acanthamoeba

Acanthamoeba keratitis is an aggressive and rapidly progressing ocular pathology whose main risk factor is the use of contact lenses. An early and differential diagnosis is considered the main factor to prevent the progression and improve the prognosis of the pathology. However, current diagnosis techniques require time, complex and costly materials making an early diagnosis challenging. Thus, there is a need for fast, accessible, and accurate methods for Acanthamoeba detection by practitioners for timely and suitable treatment and even for contact lens user as preventive diagnosis. Here, we developed a dual-mode colorimetric-based method for fast, visual, and accurate detection of Acanthamoeba using gold nanoparticles (AuNPs). For this strategy, AuNPs were functionalized with thiolated probes and the presence of target Acanthamoeba genomic sequences, produce a colorimetric change from red to purple. This approach allows the detection of 0.02 and 0.009 μM of the unamplified Acanthamoeba genome by the naked eye in less than 20 min and by color analysis using a smartphone. Additionally, real samples were successfully analyzed showing the potential of the technology considering the lack of point-of-care tools that are mostly needed.

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.

A Fluorometric Assay for the In Vitro Evaluation of Activity against Naegleria fowleri Cysts

Primary amoebic meningoencephalitis (PAM) is a lethal and rapid infection that affects the central nervous system and is caused by the free-living amoeba Naegleria fowleri. The life cycle of this protozoa consists of three different stages: The trophozoite, flagellate and cyst stages. Currently, no fully effective molecules have been found to treat PAM. In the search of new antiamoebic molecules, most of the efforts have focused on the trophozoidal activity of the compounds. However, there are no reports on the effect of the compounds on the N. fowleri cyst viability. In the present study, the cysticidal activity of four different molecules was evaluated using an alamarBlue based fluorometric assay. All the tested compounds were active against the cyst stage of N. fowleri. In fact, all the molecules except the amphotericin B, showed highest activity toward the cyst stage than the trophozoite stage. This work could be an effective protocol to select molecules with cysticidal and trophozoidal activity that can be considered a future PAM treatment. IMPORTANCE In the search of new anti-Naegleria fowleri compounds, most of the works focus on the activity of different molecules against the trophozoite stage; however, none of them include the effect of those compounds on the cyst viability. This manuscript presents a solid and reliable assay to evaluate the activity of compounds against the cyst stage of N. fowleri.

Molecular identification and genotyping of Acanthamoeba spp., in bronchoalveolar lavage fluid from immunocompetent patients with chronic respiratory disorders (CRD)

This study aimed to investigate the presence and genotyping of Acanthamoeba spp., in the bronchoalveolar lavage fluid (BALF) of immunocompetent patients with chronic respiratory disorders (CRD). In this study, 211 BALF samples were collected from patients with CRD during the COVID-19 pandemic who were candidates for fiberoptic bronchoscopy (FOB) at Imam Khomeini Hospital, Sari, Mazandaran Province, northern Iran and investigated for Acanthamoeba spp., by PCR. A total of 211 FBAL samples were examined; 5 (5/211; 2.36%) were positive by using the PCR test for Acanthamoeba spp. According to sequence analysis, three strains belonged to the T4 genotype and one strain to the T2 genotype. Our data demonstrate that the presence of Acanthamoeba (T4 and T2) in BALF specimens of patients with respiratory infections. However, it is important to note that these findings may be merely accidental. Our findings suggest further investigation to fully understand the role of Acanthamoeba spp. in the pathogenesis of lung infections.

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.

Antiamoebic Properties of Laboratory and Clinically Used Drugs against Naegleria fowleri and Balamuthia mandrillaris

Naegleria fowleri and Balamuthia mandrillaris are pathogenic free-living amoebae that infect the central nervous system with over 95% mortality rates. Although several compounds have shown promise in vitro but associated side effects and/or prolonged approval processes for clinical applications have led to limited success. To overcome this, drug repurposing of marketed compounds with known mechanism of action is considered a viable approach that has potential to expedite discovery and application of anti-amoebic compounds. In fact, many of the drugs currently employed in the treatment of N. fowleri and B. mandrillaris, such as amphotericin B, fluconazole, rifampin and miltefosine, are repurposed drugs. Here, we evaluated a range of clinical and laboratory compounds including metformin, quinclorac, indaziflam, inositol, nateglinide, 2,6-DNBT, trans-cinnamic acid, terbuthylazine, acarbose, glimepiride, vildagliptin, cellulase, thaxtomin A, repaglinide and dimethyl peptidase (IV) inhibitor against N. fowleri and B. mandrillaris. Anti-amoebic assays revealed that indaziflam, nateglinide, 2,6-DNBT, terbuthylazine, acarbose and glimepiride exhibited potent amoebicidal properties against both N. fowleri and B. mandrillaris. Notably, all compounds tested showed minimal human (HaCaT) cell cytotoxicity as determined by lactate dehydrogenase release. Prospective research using animal models is warranted to determine the potential of these repurposed compounds, as well as the need for investigating the intranasal route of delivery to treat these devastating infections.

Neurotrophic Factors in Experimental Cerebral Acanthamoebiasis

To date, no studies have addressed the role of neurotrophins (NTs) in Acanthamoeba spp. infections in the brain. Thus, to clarify the role of NTs in the cerebral cortex and hippocampus during experimental acanthamoebiasis in relation to the host immune status, the purpose of this study was to determine whether Acanthamoeba spp. may affect the concentration of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) in brain structures. Our results suggest that at the beginning of infection in immunocompetent hosts, BDNF and NT-3 may reflect an endogenous attempt at neuroprotection against Acanthamoeba spp. infection. We also observed a pro-inflammatory effect of NGF during acanthamoebiasis in immunosuppressed hosts. This may provide important information for understanding the development of cerebral acanthamoebiasis related to the immunological status of the host. However, the pathogenesis of brain acanthamoebiasis is still poorly understood and documented and, therefore, requires further research.

Cutaneous balamuthiasis: A clinicopathological study

Introduction

Methods

Results

Conclusion

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.

An annotated checklist of the eukaryotic parasites of humans, exclusive of fungi and algae

The classification of "parasites" in the medical field is a challenging notion, a group which historically has included all eukaryotes exclusive of fungi that invade and derive resources from the human host. Since antiquity, humans have been identifying and documenting parasitic infections, and this collective catalog of parasitic agents has expanded considerably with technology. As our understanding of species boundaries and the use of molecular tools has evolved, so has our concept of the taxonomy of human parasites. Consequently, new species have been recognized while others have been relegated to synonyms. On the other hand, the decline of expertise in classical parasitology and limited curricula have led to a loss of awareness of many rarely encountered species. Here, we provide a comprehensive checklist of all reported eukaryotic organisms (excluding fungi and allied taxa) parasitizing humans resulting in 274 genus-group taxa and 848 species-group taxa. For each species, or genus where indicated, a concise summary of geographic distribution, natural hosts, route of transmission and site within human host, and vectored pathogens are presented. Ubiquitous, human-adapted species as well as very rare, incidental zoonotic organisms are discussed in this annotated checklist. We also provide a list of 79 excluded genera and species that have been previously reported as human parasites but are not believed to be true human parasites or represent misidentifications or taxonomic changes.

Three encephalitis-causing amoebae and their distinct interactions with the host

Naegleria fowleri, Balamuthia mandrillaris, and Acanthamoeba spp. can cause devastating brain infections in humans which almost always result in death. The symptoms of the three infections overlap, but brain inflammation and the course of the disease differ, depending on the amoeba that is responsible. Understanding the differences between these amoebae can result in the development of strategies to prevent and treat these infections. Recently, numerous scientific advancements have been made in the understanding of pathogenicity mechanisms in general, and the basic biology, epidemiology, and the human immune response towards these amoebae in particular. In this review, we combine this knowledge and aim to identify which factors can explain the differences between the lethal brain infections caused by N. fowleri, B. mandrillaris, and Acanthamoeba spp.

Polyaniline-Conjugated Boron Nitride Nanoparticles Exhibiting Potent Effects against Pathogenic Brain-Eating Amoebae

Free-living amoebae include Acanthamoeba castellanii and Naegleria fowleri that are opportunistic protozoa responsible for life-threatening central nervous system infections with mortality rates over 90%. The rising number of cases and high mortality rates are indicative of the critical unmet need for the development of efficient drugs in order to avert future deaths. In this study, we assess the anti-amoebic capacity of a conducting polymer nanocomposite comprising polyaniline (PANI) and hexagonal boron nitride (hBN) against A. castellanii and N. fowleri. We observed significant amoebicidal and cysticidal effects using 100 μg/mL PANI/hBN (P < 0.05). Further, the nanocomposite demonstrated negligible cytotoxicity toward HaCaT and primary human corneal epithelial cells (pHCECs). In evaluating the mode of inhibition of A. castellanii due to treatment with PANI/hBN, increased intracellular reactive oxygen species (ROS) was measured and scanning microscopy visualized the formation of pores in the amoebae. Overall, this study is suggestive of the potential of the PANI/hBN nanocomposite as a promising therapy for amoeba infections.

Molecular Identification of Pathogenic Free-Living Amoeba from Household Biofilm Samples in Iran: A Risk Factor for Acanthamoeba Keratitis

Free-living amoeba (FLA) are ubiquitously distributed in the environment. However, they are also the causative agents of opportunistic infections in humans and other animals. A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. Moreover, FLA have been detected in various biofilms around the world. Therefore, the present study aimed to check for presence of FLA in samples from household biofilms in Iran and to characterize them at the molecular level. A total of 69 biofilm samples collected from showerheads, kitchen areas, and bathroom sinks were analyzed. Positive samples for FLA were characterized at the morphological and molecular levels. Furthermore, the results of morphology analysis indicated that 26.08% (18/69) of biofilm samples were positive for Acanthamoeba spp., Vermamoeba genus, and Vahlkampfiids. According to sequence analysis, five strains of Acanthamoeba isolates related to the T4 genotype and two strains belonged to the T2 genotype. In addition, the pathogenic potential of Acanthamoeba-positive isolates was conducted using the tolerance ability test. The results of BLASTn of Vermamoeba sequences were similar to what was expected for Vermamoeba vermiformis. The above-mentioned reasons revealed that the relative high contamination of household biofilm samples with FLA may pose a risk for people using soft contact lenses and for patients with traumatic cataract. Our finding proposes that filtration should be performed in shower heads and indicates the need to monitor people at increased risk of Acanthamoeba keratitis.

Opportunistic free-living amoebal pathogens

Pathogenic free-living amoebae affecting the central nervous system are known to cause granulomatous amoebic encephalitis (GAE) or primary amoebic meningoencephalitis (PAM). Although hosts with impaired immunity are generally at a higher risk of severe disease, amoebae such as Naegleria fowleri and Balamuthia mandrillaris can instigate disease in otherwise immunocompetent individuals, whereas Acanthamoeba species mostly infect immunocompromised people. Acanthamoeba also cause a sight-threatening eye infection, mostly in contact lens wearers. Although infections due to pathogenic amoebae are considered rare, recently, these deadly amoebae were detected in water supplies in the USA. This is of particular concern, especially with global warming further exacerbating the problem. Herein, we describe the epidemiology, presentation, diagnosis, and management of free-living amoeba infections.

Primary Amoebic Meningoencephalitis by Naegleria fowleri: Pathogenesis and Treatments

Naegleria fowleri is a free-living amoeba (FLA) that is commonly known as the "brain-eating amoeba." This parasite can invade the central nervous system (CNS), causing an acute and fulminating infection known as primary amoebic meningoencephalitis (PAM). Even though PAM is characterized by low morbidity, it has shown a mortality rate of 98%, usually causing death in less than two weeks after the initial exposure. This review summarizes the most recent information about N. fowleri, its pathogenic molecular mechanisms, and the neuropathological processes implicated. Additionally, this review includes the main therapeutic strategies described in case reports and preclinical studies, including the possible use of immunomodulatory agents to decrease neurological damage.

Nanovehicles in the improved treatment of infections due to brain-eating amoebae

Pathogenic free-living amoebae are known to cause fatal central nervous system infections with extremely high mortality rates. High selectivity of the blood-brain barrier hampers delivery of drugs and untargeted delivery of drugs can cause severe side effects. Nanovehicles can be used for targeted drug delivery across the blood-brain barrier. Inorganic nanoparticles have been explored as carriers for various biomedical applications and can be modified with various ligands for efficient targeting and cell selectivity while lipid-based nanoparticles have been extensively used in the development of both precision and colloidal nanovehicles. Nanomicelles and polymeric nanoparticles can also serve as nanocarriers and may be modified so that responsiveness of the nanoparticles and release of the loads are linked to specific stimuli. These nanoparticles are discussed here in the context of the treatment of central nervous system infections due to pathogenic amoebae. It is anticipated that these novel strategies can be utilized in tandem with novel drug leads currently in the pipeline and yield in the development of much needed treatments against these devastating parasites.

Encephalitis and Brain Abscess

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

On the diversity and clinical importance of Acanthamoeba spp. from Group 1

Group 1 acanthamoebae are morphologically and phylogenetically distinct from all other Acanthamoeba species. They include five species, each labelled by its genotype: A. astronyxis (T7), A. tubiashi (T8), A. comandoni (T9), unnamed Acanthamoeba sp. (T17), and A. byersi (T18). Thought only environmental, they have recently attracted attention due to their recovery in cases of human keratitis and encephalitis, the main diseases caused by Acanthamoeba, where the usual causative agents are mainly species of Groups 2 and 3. Analysis of the available data confirms the pathogenic importance of these species, although it is probably minor compared to that of the species in Groups 2 and 3. In addition, it should be noted that there are difficulties in identifying genotypes by widely used molecular methods, and some misidentifications are revealed.

Detection of Free-Living Amoebae and Their Intracellular Bacteria in Borehole Water before and after a Ceramic Pot Filter Point-of-Use Intervention in Rural Communities in South Africa

Free-living amoebae (FLA) are ubiquitous in nature, whereas amoeba-resistant bacteria (ARB) have evolved virulent mechanisms that allow them to resist FLA digestion mechanisms and survive inside the amoeba during hostile environmental conditions. This study assessed the prevalence of FLA and ARB species in borehole water before and after a ceramic point-of-use intervention in rural households. A total of 529 water samples were collected over a five-month period from 82 households. All water samples were subjected to amoebal enrichment, bacterial isolation on selective media, and molecular identification using 16S PCR/sequencing to determine ARB species and 18S rRNA PCR/sequencing to determine FLA species present in the water samples before and after the ceramic pot intervention. Several FLA species including Acanthamoeba spp. and Mycobacterium spp. were isolated. The ceramic pot filter removed many of these microorganisms from the borehole water. However, design flaws could have been responsible for some FLA and ARB detected in the filtered water. FLA and their associated ARB are ubiquitous in borehole water, and some of these species might be potentially harmful and a health risk to vulnerable individuals. There is a need to do more investigations into the health risk of these organisms after point-of-use treatment.

Derivatisation of metronidazole enhances cytotoxic effect against Acanthamoeba genotype T4 isolates and leads to cytomorphological changes in trophozoites

Amoebae of the genus Acanthamoeba are worldwide distributed causative agents of serious human infections such as granulomatous amoebic encephalitis (GAE) and Acanthamoeba keratitis (AK). To date, treatment of these infections is non-uniform and frequently unsuccessful. Recently, the phosphonium salts were studied for their high levels of antimicrobial activity. This work was aimed to investigate the cytotoxic effect of metronidazole and two phosphonium salts (PS1, PS2) on two clinical Acanthamoeba isolates. The isolates showed distinctly higher susceptibility to both phosphonium salts than to metronidazole. The highest susceptibility was noted to PS1 after 48 h of incubation. Metronidazole derivate PS2 showed higher susceptibility than metronidazole. The values of EC₅₀ of PS2 were approximately twenty times lower than EC₅₀ of metronidazole for Acanthamoeba lugdunensis strain and sixteen times lower for Acanthamoeba quina strain after 48 h. Although the therapeutic effect of metronidazole in Acanthamoeba infections is usually insufficient, its derivatisation can result in a significantly higher amoebicidal effect. Cytomorphological changes of trophozoites after exposure to tested compounds included rounding up of the cells, damage of membrane integrity, presence of pathological protrusions, elongation of the cells or pseudocyst-like stages. Obtained results indicate possible therapeutic potential of studied phosphonium salts.

Immunopathogenicity of Acanthamoeba spp. in the Brain and Lungs

Free-living amoebas, including Acanthamoeba spp., are widely distributed in soil, water, and air. They are capable of causing granulomatous amebic encephalitis, Acanthamoeba pneumonia, Acanthamoeba keratitis, and disseminated acanthamoebiasis. Despite low occurrence worldwide, the mortality rate of Acanthamoeba spp. infections is very high, especially in immunosuppressed hosts. Acanthamoeba infections are a medical problem, owing to limited improvement in diagnostics and treatment, which is associated with incomplete knowledge of pathophysiology, pathogenesis, and the host immune response against Acanthamoeba spp. infection. The aim of this review is to present the biochemical and molecular mechanisms of Acanthamoeba spp.-host interactions, including the expression of Toll-like receptors, mechanisms of an immune response, the activity of metalloproteinases, the secretion of antioxidant enzymes, and the expression and activity of cyclooxygenases. We show the relationship between Acanthamoeba spp. and the host at the cellular level and host defense reactions that lead to changes in the selected host's organs.

Evaluation of the occurrence of pathogenic free-living amoeba and bacteria in 20 public indoor swimming pool facilities

Recently, indoor swimming pool activities have increased to promote health-enhancing physical activities, which require establishing suitable protocols for disinfection and water quality control. Normally, the assessment of the microbial quality of the water in the pools only considers the presence of different bacteria. However, other less frequent but more resistant pathogens, such as free-living amoebas (FLA), are not contemplated in both existing recommendation and research activities. FLA represent a relevant human health risk, not only due to their pathogenicity but also due to the ability to act as vehicles of other pathogens, such as bacteria. Therefore, this work aimed to study the physicochemical characteristics and the occurrence of potentially pathogenic FLA and bacteria in water samples from 20 public indoor swimming facilities in Northern Portugal. Our results showed that some swimming pools presented levels of pH, free chlorine, and conductivity out of the recommended limits. Pathogenic FLA species were detected in two of the facilities under study, where we also report the presence of both, FLA and pathogenic bacteria. Our findings evidence the need to assess the occurrence of FLA and their existence in the same environmental niche as pathogenic bacteria in swimming pool facilities worldwide and to establish recommendations to safeguard the health of the users.

Free-living amoebae and other neglected protistan pathogens: Health emergency signals?

Protistan parasites have an undisputed global health impact. However, outside of a few key exceptions, e.g. the agent of malaria, most of these infectious agents are neglected as important health threats. The Symposium entitled "Free-living amoebae and neglected pathogenic protozoa: health emergency signals?" held at the European Congress of Protistology in Rome, July 2019, brought together researchers addressing scientific and clinical questions about some of these fascinating organisms. Topics presented included the molecular basis of pathogenicity in Acanthamoeba; genomics of Naegleria fowleri; and epidemiology of poorly diagnosed enteric protistan species, including Giardia, Cryptosporidium, Blastocystis, Dientamoeba. The Symposium aim was to excite the audience about the opportunities and challenges of research in these underexplored organisms and to underline the public health implications of currently under-appreciated protistan infections. The major take home message is that any knowledge that we gain about these organisms will allow us to better address them, in terms of monitoring and treatment, as sources of future health emergencies.

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.

Molecular detection of Acanthamoeba spp. in Seven Crater Lakes of Laguna, Philippines

Acanthamoeba spp. are ubiquitous free-living amoeba with genotypes that cause severe pathology of the eyes, central nervous systems, and rare reports of cutaneous infections. The Seven Crater Lakes are freshwater water resources in Laguna, Philippines primarily used for aquaculture and tourism. A total of 16 surface water samples were collected from different sampling areas per Crater Lake and placed in sterile plastic containers. Samples were filtered using 1.2 μm pore size, glass microfiber filter. Filtered sediments were placed on non-nutrient agar lawned with Escherichia coli and incubated aerobically at 35 °C for 14 days. Six out of 16 water samples exhibited amoebic growth. Cystic stages revealed circular to stellate morphology under light microscopy which were initially classified as Acanthamoeba spp. DNA from positive isolates were made to react with polymerase chain reaction using Acanthamoeba specific primers JDP1 5′-GGCCCAGATCGTTTACCGTGAA-3′ and JDP2 5′-TCTCACAAGCTGCTAGGGAGTCA-3′confirmed the presence of several Acanthamoeba species. Phylogenetic analysis revealed the presence of seven isolates belonging to Acanthamoeba genotypes T4, T5, and T9. The presence of potentially pathogenic Acanthamoeba genotypes in the Seven Crater Lakes of Laguna signifies risk to human health which necessitates the development of programs, policies, and guidelines on the understanding, prevention, and management of potential human infections.

Aryl Quinazolinone Derivatives as Novel Therapeutic Agents against Brain-Eating Amoebae

Naegleria fowleri and Balamuthia mandrillaris are protist pathogens that infect the central nervous system, causing primary amoebic meningoencephalitis and granulomatous amoebic encephalitis with mortality rates of over 95%. Quinazolinones and their derivatives possess a wide spectrum of biological properties, but their antiamoebic effects against brain-eating amoebae have never been tested before. In this study, we synthesized a variety of 34 novel arylquinazolinones derivatives (Q1-Q34) by altering both quinazolinone core and aryl substituents. To study the antiamoebic activity of these synthetic arylquinazolinones, amoebicidal and amoebistatic assays were performed against N. fowleri and B. mandrillaris. Moreover, amoebae-mediated host cells cytotopathogenicity and cytotoxicity assays were performed against human keratinocytes cells in vitro. The results revealed that selected arylquinazolinones derivatives decreased the viability of B. mandrillaris and N. fowleri significantly (P < 0.05) and reduced cytopathogenicity of both parasites. Furthermore, these compounds were also found to be least cytotoxic against HaCat cells. Considering that nanoparticle-based materials possess potent in vitro activity against brain-eating amoebae, we conjugated quinazolinones derivatives with silver nanoparticles and showed that activities of the drugs were enhanced successfully after conjugation. The current study suggests that quinazolinones alone as well as conjugated with silver nanoparticles may serve as potent therapeutics against brain-eating amoebae.

Metronidazole conjugated magnetic nanoparticles loaded with amphotericin B exhibited potent effects against pathogenic Acanthamoeba castellanii belonging to the T4 genotype

Acanthamoeba castellanii can cause granulomatous amoebic encephalitis and Acanthamoeba keratitis. Currently, no single drug has been developed to effectively treat infections caused by Acanthamoeba. Recent studies have shown that drugs conjugated with nanoparticles exhibit potent in vitro antiamoebic activity against pathogenic free-living amoebae. In this study, we have developed a nano drug delivery system based on iron oxide nanoparticles conjugated with metronidazole which were further loaded with amphotericin B to produce enhanced antiamoebic effects against Acanthamoeba castellanii. The results showed that metronidazole-nanoparticles-amphotericin B (Met-MNPs-Amp) significantly inhibited the viability of these amoebae as compared to the respective controls including drugs and nanoparticles alone. Met-MNPs-Amp exhibited IC₅₀ at 50 μg/mL against both A. castellanii trophozoites and cysts. Furthermore, these nanoparticles did not affect the viability of rat and human cells and showed safe hemolytic activity. Hence, the results obtained in this study have potential utility in drug development against infections caused by Acanthamoeba castellanii. A combination of drugs can lead to successful prognosis against these largely neglected infections. Future studies will determine the value of conjugating molecules with diagnostic and therapeutic potential to provide theranostic approaches against these serious infections.

Schwann Cell Autophagy and Necrosis as Mechanisms of Cell Death by Acanthamoeba

Amoebae of the genus Acanthamoeba are etiological agents of granulomatous amoebic encephalitis (GAE). Recently, through an in vivo GAE model, Acanthamoeba trophozoites were immunolocalized in contact with the peripheral nervous system (PNS) cells-Schwann cells (SC). In this study, we analyzed in greater detail the in vitro early morphological events (1, 2, 3, and 4 h) during the interaction of A. culbertsoni trophozoites (ATCC 30171) with SC from Rattus norvegicus (ATCC CRL-2941). Samples were processed for scanning and transmission electron microscopy as well as confocal microscopy. After 1 h of interaction, amoebae were observed to be adhered to the SC cultures, emitting sucker-like structures associated with micro-phagocytic channels. In addition, evidence of necrosis was identified since edematous organelles as well as multivesicular and multilamellar bodies characteristics of autophagy were detected. At 2 h, trophozoites migrated beneath the SC culture in which necrosis and autophagy persisted. By 3 and 4 h, extensive lytic zones were observed. SC necrosis was confirmed by confocal microscopy. We reported for the first time the induction of autophagic and necrotic processes in PNS cells, associated in part with the contact-dependent pathogenic mechanisms of A. culbertsoni trophozoites.

Gold-Conjugated Curcumin as a Novel Therapeutic Agent against Brain-Eating Amoebae

Balamuthia mandrillaris and Naegleria fowleri are free-living amoebae that cause infection of the central nervous system, granulomatous amoebic encephalitis (GAE) and primary amoebic meningoencephalitis (PAM), respectively. The fact that mortality rates for cases of GAE and PAM are more than 95% indicates the need for new therapeutic agents against those amoebae. Considering that curcumin exhibits a wide range of biological properties and has shown efficacy against Acanthamoeba castellanii, we evaluated the amoebicidal properties of curcumin against N. fowleri and B. mandrillaris. Curcumin showed significant amoebicidal activities with an AC50 of 172 and 74 μM against B. mandrillaris and N. fowleri, respectively. Moreover, these compounds were also conjugated with gold nanoparticles to further increase their amoebicidal activities. After conjugation with gold nanoparticles, amoebicidal activities of the drugs were increased by up to 56 and 37% against B. mandrillaris and N. fowleri, respectively. These findings are remarkable and suggest that clinically available curcumin and our gold-conjugated curcumin nanoparticles hold promise in the improved treatment of fatal infections caused by brain-eating amoebae and should serve as a model in the rationale development of therapeutic interventions against other infections.

Evaluation of Indolocarbazoles from Streptomyces sanyensis as a Novel Source of Therapeutic Agents against the Brain-Eating Amoeba Naegleria fowleri

Naegleria fowleri is an opportunistic pathogenic free-living amoeba which is able to rapidly colonize the central nervous system (CNS) and causes a lethal infection known as primary amoebic meningoencephalitis (PAM). Furthermore, more than 98% of the known cases of PAM are fatal and affect mainly children under 12 and young adults. Until now, no fully effective therapeutic agents against N. fowleri are available and hence the urgent need to find novel agents to treat PAM. At present, PAM therapy is based on the combination of amphotericin B, miltefosine, among others, with unwanted toxic effects. Recently, our team isolated various indolocarbazoles (ICZs) from the culture of a mangrove strain of Streptomyces sanyensis which showed activity against kinetoplastids and the Acanthamoeba genus. Hence, in this study, the activity of the previously isolated ICZs, staurosporine (STS), 7-oxostaurosporine (7OSTS), 4′-demethylamino-4′-oxostaurosporine, and streptocarbazole B, was evaluated against two type strains of N. fowleri. Furthermore, the performed activity assays revealed that STS was the most active ICZ presenting an inhibitory concentration 50 (IC₅₀) of 0.08 ± 0.02 µM (SI 109.3). Moreover, STS induced programmed cell death (PCD) in the treated amoebae by triggering DNA condensation, mitochondrial disfunction, cell membrane disruption, and reactive oxygen species (ROS) generation. Therefore, STS could be a promising therapeutic agent against PAM.

Novel Azoles as Antiparasitic Remedies against Brain-Eating Amoebae

Balamuthia mandrillaris and Naegleria fowleri are opportunistic protozoan pathogens capable of producing infection of the central nervous system with more than 95% mortality rate. Previously, we have synthesized several compounds with antiamoebic properties; however, synthesis of compounds that are analogues of clinically used drugs is a highly desirable approach that can lead to effective drug development against these devastating infections. In this regard, compounds belonging to the azole class possess wide range of antimicrobial properties and used clinically. In this study, six novel benzimidazole, indazole, and tetrazole derivatives were synthesized and tested against brain-eating amoebae. These compounds were tested for their amoebicidal and static properties against N. fowleri and B. mandrillaris. Furthermore, the compounds were conjugated with silver nanoparticles and characterized. The synthetic heterocyclic compounds showed up to 72% and 65% amoebicidal activities against N. fowleri and B. mandrillaris respectively, while expressing up to 75% and 70% amoebistatic activities, respectively. Following conjugation with silver nanoparticles, amoebicidal activities of the drugs increased by up to 46 and 36% versus B. mandrillaris and N. fowleri. Minimal effects were observed when the compounds were evaluated against human cells using cytotoxicity assays. In summary, azole compounds exhibited potent activity against N. fowleri and B. mandrillaris. Moreover, conjugation of the azole compounds with silver nanoparticles further augmented the capabilities of the compounds against amoebae.

Identification of T3 and T4 Genotypes of Acanthamoeba sp. in Dust Samples Isolated from Air Conditioning Equipment of Public Hospital of Ituiutaba-MG

The free-living amoebae are currently considered an emerging parasitic infection. The infection by this protozoan can generate serious infection and even cause death. Due to their amphizoic and opportunistic characters of these microorganisms, one should give more attention, not only in swimming pools but also where there are immunologically susceptible patients such as those found in intensive care units and surgical centers. Due to their difficult diagnosis often postmortem, because they are considered to be an emerging parasitic infection and their diagnosis is difficult, often performed post mortem. This study aimed to evaluate the safety of these protozoa in air conditioners by taking samples of dust from both the surgical center and the intensive therapy unit. We analyzed 48 dust samples that were collected from six air conditioners equipment located in the Intensive Care Unit (ICU) and Surgical Center (SC) of a public hospital. We found 10.4% of the samples collected in the SC, and 75% of the samples collected in the ICU presented free-living amoeba cysts by light microscopy analysis. In total, 35.4% (17/48) of the air conditioning samples of the hospital were positive and, by PCR, were identified to belong to the genus Acanthamoeba spp and Balamuthia mandrillaris species. By DNA sequencing analysis, it was possible to classify the Acanthamoeba samples as belonging to the T3 and T4 genotypes. These genotypes are the main cause of keratitis in humans, and Balamuthia may cause amoebic encephalitis, and together are emerging parasitic infections. Our results show the presence of the two most important amoebas Acanthamoeba (T3 and T4 genotypes) and Balamuthia in the SC and the ICU, and these necessary precautions these sites could be propagating cysts of these amoebas and patients during their stay or discharge could present ocular and NSC alterations without perhaps arriving to the diagnosis of free-living amoeba infection.

Fatal granulomatous amoebic encephalitis due to free-living amoebae in two boys in two different hospitals in Lima, Perú

Granulomatous amoebic encephalitis caused by free-living amoebae is a rare condition that is difficult to diagnose and hard to treat, generally being fatal. Anti-amoebic treatment is often delayed because clinical signs and symptoms may hide the probable causing agent misleading the appropriate diagnostic test. There are four genera of free-living amoeba associated with human infection, Naegleria, Acanthamoeba sp., Balamuthia and Sappinia. Two boys were admitted with diagnosis of acute encephalitis. The history of having been in contact with swimming pools and rivers, supports the suspicion of an infection due to free-living amoebae. In both cases a brain biopsy was done, the histology confirmed granulomatous amoebic encephalitis with the presence of amoebic trophozoites.

Detection of Naegleria fowleri, Acanthamoeba spp, and Balamuthia mandrillaris in Formalin-Fixed, Paraffin-Embedded Tissues by Real-Time Multiplex Polymerase Chain Reaction

OBJECTIVES

Pathogenic free-living amebae (FLAs) cause skin, ocular, and central nervous system (CNS) infections with significant morbidity and mortality. Diagnosis of FLA infections by pathologic examination of tissue sections can be aided using molecular assays. This study investigated the performance characteristics of a multiplex real-time polymerase chain reaction (PCR) assay (FLA-PCR) for detection and differentiation of FLAs in clinical specimens.

METHODS

FLA-PCR was performed on 39 human specimens comprising one cutaneous, 14 corneal, and 24 CNS formalin-fixed, paraffin-embedded (FFPE) tissues with a histopathologic diagnosis of FLA infection and four CNS FFPE tissues with inflammation but no evidence of FLAs. In addition, clinical specificity and assay limit of detection were determined.

RESULTS

FLA detection sensitivities ranged from 79% to 84% in FFPE tissues. No cross-reactivity was observed.

CONCLUSIONS

While sensitivity is limited, FLA-PCR assay may serve as a useful adjunct for detection or confirmation of FLA infections in FFPE tissues.

Brain-eating Amoebae Infection: Challenges and Opportunities in Chemotherapy

Pathogenic free-living amoeba are known to cause a devastating infection of the central nervous system and are often referred to as "brain-eating amoebae". The mortality rate of more than 90% and free-living nature of these amoebae is a cause for concern. It is distressing that the mortality rate has remained the same over the past few decades, highlighting the lack of interest by the pharmaceutical industry. With the threat of global warming and increased outdoor activities of public, there is a need for renewed interest in identifying potential anti-amoebic compounds for successful prognosis. Here, we discuss the available chemotherapeutic options and opportunities for potential strategies in the treatment and diagnosis of these life-threatening infections.

In Vitro Activity of Statins against Naegleria fowleri

Naegleria fowleri causes a deadly disease called primary amoebic meningoencephalitis (PAM). Even though PAM is still considered a rare disease, the number of reported cases worldwide has been increasing each year. Among the factors to be considered for this, awareness about this disease, and also global warming, as these amoebae thrive in warm water bodies, seem to be the key factors. Until present, no fully effective drugs have been developed to treat PAM, and the current options are amphotericin B and miltefosine, which present side effects such as liver and kidney toxicity. Statins are able to inhibit the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, which is a key enzyme for the synthesis of ergosterol of the cell membrane of these amoebae. Therefore, the in vitro activity of a group of statins was tested in this study against two types of strains of Naegleria fowleri. The obtained results showed that fluvastatin was the most effective statin tested in this study and was able to eliminate these amoebae at concentrations of 0.179 ± 0.078 to 1.682 ± 0.775 µM depending on the tested strain of N. fowleri. Therefore, fluvastatin could be a potential novel therapeutic agent against this emerging pathogen.