Primary amoebic meningo-encephalitis: clinical, pathological and epidemiological features of six fatal cases

Understanding the pathogenicity of Naegleria fowleri in association with N. fowleri antigen-1 (Nfa1)

Naegleria fowleri, a brain-eating amoeba, thrives in lakes and rivers with aquatic vegetation and causes primary amoebic meningoencephalitis (PAM) in humans. Most recently, it has become such a serious problem that N. fowleri was detected in tap water in Houston, USA. Several pathogenic factors are considered very important to destroy target cells in the brain. In particular, the food-cup where N. fowleri antigen-1 (Nfa1) is located, is strongly expressed in pseudopodia involved in the movement of N. fowleri, and is involved in phagocytosis by attaching to target cells. In this article, we reviewed the role of the Nfa1 protein and its associated pathogenicity. The nfa1 gene was cloned by cDNA library immunoscreening using infection serum and immune serum. Nfa1 protein is mainly distributed in pseudopodia important to movement and vacuoles. Moreover, heat shock protein 70, cathepsin-like proteare and Nf-actin are also associated with pseudopodia in which Nfa1 is localized. Interestingly, the amount of the nfa1 gene changed as N. fowleri trophozoites transformed into cysts. Polyclonal antiserum against Nfa1 showed a protective effect against cytotoxicity of approximately 19.7%. Nfa1-specific IgA antibodies prevent N. fowleri trophozoites from adhering to the nasal mucosa, delaying invasion. The nfa1-vaccinated mice showed significantly higher levels of Nfa1-specific antibody. The duration of anti-Nfa1 IgG in the vaccinated mice lasted 12 weeks, strongly suggesting that nfa1 is a significant pathogenic gene and that Nfa1 is a pathogenic protein. Several factors related to pseudopodia and locomotion have been linked to Nfa1. A clearer function of N. fowleri targeting nfa1 with other genes might enable target-based inhibition of N. fowleri pathogenicity.

A primary amoebic meningoencephalitis case associated with swimming in seawater

This case report describes a 62-year-old male fisherman who presented with persistent vomiting, headache, and behavior changes. Despite initial antibiotic and corticosteroid treatment, his condition worsened, leading to coma and subsequent death. Macro-genome sequencing of cerebrospinal fluid (CSF) revealed the presence of Naegleria fowleri infection, which had been missed during initial laboratory tests. The patient's exposure history included sea-swimming near Zhoushan Island.

Isolation and identification of Acanthamoeba genotypes and Naegleria spp. from the water samples of public swimming pools in Qazvin, Iran

Free-living amoeba (FLA), including Acanthamoeba and Naegleria are facultative parasites in humans. The amoeba have widespread distribution in various water sources. The aim of this study was isolation and molecular identification of Acanthamoeba and Naegleria isolated from swimming pools and also hot and cold tub waters in Qazvin province. The samples (166 water samples) were cultured to isolate and identify positive specimens. PCR (polymerase chain reaction) amplification, sequencing and phylogenetic analysis were conducted to confirm the isolated species and genotypes of amoeba. According to morphological characterizations, 18.6% of specimens were identified as FLA, which in 71% were Acanthamoeba by PCR method. Molecular analysis revealed that 36.3%, 18.1% and 4.5% of Acanthamoeba specimens were identified as T3, T4 and T11 Acanthamoeba genotypes, respectively. Protacanthamoeba bohemica (27.2%) and Acanthamoeba sp. (4.5%) were found among the specimens. The results of osmo-tolerance and thermo-tolerance assays demonstrated that 50% of T3 and 25% of T4 genotypes of Acanthamoeba were highly pathogenic parasites. The molecular approach showed the presence of Naegleria lovaniensis (9%) in hot tub water of swimming pools. This study demonstrated that the swimming pools and hot tub water in Qazvin province were contaminated with Acanthamoeba and Naegleria species.

Identification of differential protein recognition pattern between Naegleria fowleri and Naegleria lovaniensis

Many pathogenicity factors are involved in the development of primary amoebic meningoencephalitis (PAM) caused by N fowleri. However, most of them are not exclusive for N fowleri and they have not even been described in other nonpathogenic Naegleria species. Therefore, the objective of this work was to identify differential proteins and protein pattern recognition between Naegleria fowleri and Naegleria lovaniensis using antibodies anti-N fowleri as strategy to find vaccine candidates against meningoencephalitis. Electrophoresis and Western blots conventional and 2-DE were performed for the identification of antigenic proteins, and these were analysed by the mass spectrometry technique. The results obtained in 2-DE gels and Western blot showed very notable differences in spot intensity between these two species, specifically those with relative molecular weight of 100, 75, 50 and 19 kDa. Some spots corresponding to these molecular weights were identified as actin fragment, myosin II, heat shock protein, membrane protein Mp2CL5 among others, with differences in theoretical post-translational modifications. In this work, we found differences in antigenic proteins between both species, proteins that could be used for a further development of vaccines against N fowleri infection.

Identification of Naegleria fowleri proteins linked to primary amoebic meningoencephalitis

Naegleria fowleri (N. fowleri) causes primary amoebic meningoencephalitis, a rapidly fatal disease of the central nervous system. N. fowleri can exist in cyst, flagellate or amoebic forms, depending on environmental conditions. The amoebic form can invade the brain following introduction into the nasal passages. When applied intranasally to a mouse model, cultured N. fowleri amoebae exhibit low virulence. However, upon serial passage in mouse brain, the amoebae acquire a highly virulent state. In the present study, a proteomics approach was applied to the identification of N. fowleri amoeba proteins whose expression was associated with the highly virulent state in mice. Mice were inoculated intranasally with axenically cultured amoebae or with mouse-passaged amoebae. Examination by light and electron microscopy revealed no morphological differences. However, mouse-passaged amoebae were more virulent in mice as indicated by exhibiting a two log10 titre decrease in median infective dose 50 (ID50). Scatter plot analysis of amoebic lysates revealed a subset of proteins, the expression of which was associated with highly virulent amoebae. MS-MS indicated that this subset contained proteins that shared homology with those linked to cytoskeletal rearrangement and the invasion process. Invasion assays were performed in the presence of a select inhibitor to expand on the findings. The collective results suggest that N. fowleri gene products linked to cytoskeletal rearrangement and invasion may be candidate targets in the management of primary amoebic meningoencephalitis.

Excretory and Secretory Proteins of Naegleria fowleri Induce Inflammatory Responses in BV-2 Microglial Cells

Naegleria fowleri, a free-living amoeba that is found in diverse environmental habitats, can cause a type of fulminating hemorrhagic meningoencephalitis, primary amoebic meningoencephalitis (PAM), in humans. The pathogenesis of PAM is not fully understood, but it is likely to be primarily caused by disruption of the host's nervous system via a direct phagocytic mechanism by the amoeba. Naegleria fowleri trophozoites are known to secrete diverse proteins that may indirectly contribute to the pathogenic function of the amoeba, but this factor is not clearly understood. In this study, we analyzed the inflammatory responses in BV-2 microglial cells induced by excretory and secretory proteins of N. fowleri (NfESP). Treatment of BV-2 cells with NfESP induced the expression of various cytokines and chemokines, including the proinflammatory cytokines IL-1α and TNF-α. NfESP-induced IL-1α and TNF-α expression in BV-2 cells were regulated by p38, JNK, and ERK MAPKs. NfESP-induced IL-1α and TNF-α production in BV-2 cells were effectively downregulated by inhibition of NF-kB and AP-1. These results collectively suggest that NfESP stimulates BV-2 cells to release IL-1α and TNF-α via NF-kB- and AP-1-dependent MAPK signaling pathways. The released cytokines may contribute to inflammatory responses in microglia and other cell types in the brain during N. fowleri infection.

Meningoencephalitis due to the amoeboflagellate Naegleria fowleri in ruminants in Algeria

Primary amoebic meningoencephalitis (PAM) is a fatal infection in most cases, caused by the amoeba flagellate Naegleria fowleri. This report describes the first cases of PAM in Algeria, in a cow and a ewe from Batna, north-eastern Algeria. The death of both ruminants occurred a week after the first clinical manifestations. The cerebrospinal fluid, after staining with May-Grünwald-Giemsa, showed the presence of amoebae cells. Histological sections revealed numerous amoebae in all parts of the brain. The presence of N. fowleri was confirmed using a species-specific real-time PCR in histological tissue sections. The two PAM cases were reported during the hot season, and the source of infection is very likely the water where the cattle came to drink. Particular attention should be focused on this type of infection in aquatic environments when the temperature is high and preventive measures must be taken to avoid the proliferation of N. fowleri.

Free living amoebae and human disease

Pathogenic FLA are ubiquitous protozoans and despite frequent human contact remain a rare cause of often devastating infection with poor prognosis. Given changes in climate, human encroachment into the environment, increasing immunosuppression, and improving diagnostic capacity, it is likely we will see increased cases in the future. Early diagnosis is challenging but crucial to achieving a favourable outcome. It is best facilitated by improved awareness of FLA disease, appropriate clinical suspicion and early diagnostic testing.

Protective immunity against Naegleria fowleri infection on mice immunized with the rNfa1 protein using mucosal adjuvants

The free-living amoeba, Naegleria fowleri, causes a fatal disease called primary amoebic meningoencephalitis (PAM) in humans and experimental animals. Of the pathogenic mechanism of N. fowleri concerning host tissue invasion, the adherence of amoeba to hose cells is the most important. We previously cloned the nfa1 gene from N. fowleri. The protein displayed immunolocalization in the pseudopodia, especially the food-cups structure, and was related to the contact-dependent mechanism of the amoebic pathogenicity in N. fowleri infection. The cholera toxin B subunit (CTB) and Escherichia coli heat-labile enterotoxin B subunit (LTB) have been used as potent mucosal adjuvants via the parenteral route of immunization in most cases. In this study, to examine the effect of protective immunity of the Nfa1 protein for N. fowleri infection with enhancement by CTB or LTB adjuvants, intranasally immunized BALB/c mice were infected with N. fowleri trophozoites for the development of PAM. The mean time to death of mice immunized with the Nfa1 protein using LTB or CTB adjuvant was prolonged by 5 or 8 days in comparison with that of the control mice. In particular, the survival rate of mice immunized with Nfa1 plus CTB was 100% during the experimental period. The serum IgG levels were significantly increased in mice immunized with Nfa1 protein plus CTB or LTB adjuvants. These results suggest that the Nfa1 protein, with CTB or LTB adjuvants, induces strong protective immunity in mice with PAM due to N. fowleri infection.

Pathogens penetrating the central nervous system: infection pathways and the cellular and molecular mechanisms of invasion

The brain is well protected against microbial invasion by cellular barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). In addition, cells within the central nervous system (CNS) are capable of producing an immune response against invading pathogens. Nonetheless, a range of pathogenic microbes make their way to the CNS, and the resulting infections can cause significant morbidity and mortality. Bacteria, amoebae, fungi, and viruses are capable of CNS invasion, with the latter using axonal transport as a common route of infection. In this review, we compare the mechanisms by which bacterial pathogens reach the CNS and infect the brain. In particular, we focus on recent data regarding mechanisms of bacterial translocation from the nasal mucosa to the brain, which represents a little explored pathway of bacterial invasion but has been proposed as being particularly important in explaining how infection with Burkholderia pseudomallei can result in melioidosis encephalomyelitis.

Vaccination with lentiviral vector expressing the nfa1 gene confers a protective immune response to mice infected with Naegleria fowleri

Naegleria fowleri, a pathogenic free-living amoeba, causes fatal primary amoebic meningoencephalitis (PAM) in humans and animals. The nfa1 gene (360 bp), cloned from a cDNA library of N. fowleri, produces a 13.1-kDa recombinant protein which is located on pseudopodia, particularly the food cup structure. The nfa1 gene plays an important role in the pathogenesis of N. fowleri infection. To examine the effect of nfa1 DNA vaccination against N. fowleri infection, we constructed a lentiviral vector (pCDH) expressing the nfa1 gene. For the in vivo mouse study, BALB/c mice were intranasally vaccinated with viral particles of a viral vector expressing the nfa1 gene. To evaluate the effect of vaccination and immune responses of mice, we analyzed the IgG levels (IgG, IgG1, and IgG2a), cytokine induction (interleukin-4 [IL-4] and gamma interferon [IFN-γ]), and survival rates of mice that developed PAM. The levels of both IgG and IgG subclasses (IgG1 and IgG2a) in vaccinated mice were significantly increased. The cytokine analysis showed that vaccinated mice exhibited greater IL-4 and IFN-γ production than the other control groups, suggesting a Th1/Th2 mixed-type immune response. In vaccinated mice, high levels of Nfa1-specific IgG antibodies continued until 12 weeks postvaccination. The mice vaccinated with viral vector expressing the nfa1 gene also exhibited significantly higher survival rates (90%) after challenge with N. fowleri trophozoites. Finally, the nfa1 vaccination effectively induced protective immunity by humoral and cellular immune responses in N. fowleri-infected mice. These results suggest that DNA vaccination using a viral vector may be a potential tool against N. fowleri infection.

The immune response induced by DNA vaccine expressing nfa1 gene against Naegleria fowleri

The pathogenic free-living amoeba, Naegleria fowleri, causes fatal primary amoebic meningoencephalitis in experimental animals and in humans. The nfa1 gene that was cloned from N. fowleri is located on pseudopodia, especially amoebic food cups and plays an important role in the pathogenesis of N. fowleri. In this study, we constructed and characterized retroviral vector and lentiviral vector systems for nfa1 DNA vaccination in mice. We constructed the retroviral vector (pQCXIN) and the lentiviral vector (pCDH) cloned with the egfp-nfa1 gene. The expression of nfa1 gene in Chinese hamster ovary cell and human primary nasal epithelial cell transfected with the pQCXIN/egfp-nfa1 vector or pCDH/egfp-nfa1 vector was observed by fluorescent microscopy and Western blotting analysis. Our viral vector systems effectively delivered the nfa1 gene to the target cells and expressed the Nfa1 protein within the target cells. To evaluate immune responses of nfa1-vaccinated mice, BALB/c mice were intranasally vaccinated with viral particles of each retro- or lentiviral vector expressing nfa1 gene. DNA vaccination using viral vectors expressing nfa1 significantly stimulated the production of Nfa1-specific IgG subclass, as well as IgG levels. In particular, both levels of IgG2a (Th1) and IgG1 (Th2) were significantly increased in mice vaccinated with viral vectors. These results show the nfa1-vaccination induce efficiently Th1 type, as well as Th2 type immune responses. This is the first report to construct viral vector systems and to evaluate immune responses as DNA vaccination in N. fowleri infection. Furthermore, these results suggest that nfal vaccination may be an effective method for treatment of N. fowleri infection.

Pathogenic Naegleria fowleri and non-pathogenic Naegleria lovaniensis exhibit differential adhesion to, and invasion of, extracellular matrix proteins

Naegleria fowleri and Naegleria lovaniensis are closely related free-living amoebae found in the environment. N. fowleri causes primary amoebic meningoencephalitis (PAM), a rapidly fatal disease of the central nervous system, while N. lovaniensis is non-pathogenic. N. fowleri infection occurs when the amoebae access the nasal passages, attach to the nasal mucosa and its epithelial lining, and migrate to the brain. This process involves interaction with components of the host extracellular matrix (ECM). Since the ability to invade tissues can be a characteristic that distinguishes pathogenic from non-pathogenic amoebae, the objective of this study was to assess adhesion to, and invasion of, the ECM by these two related but distinct Naegleria species. N. fowleri exhibited a higher level of adhesion to the ECM components laminin-1, fibronectin and collagen I. Scanning electron microscopy revealed that N. fowleri attached on ECM substrata exhibited a spread-out appearance that included the presence of focal adhesion-like structures. Western immunoblotting revealed two integrin-like proteins for both species, but one of these, with a molecular mass of approximately 70 kDa, was detected at a higher level in N. fowleri. Confocal microscopy indicated that the integrin-like proteins co-localized to the focal adhesion-like structures. Furthermore, anti-integrin antibody decreased adhesion of N. fowleri to ECM components. Finally, N. fowleri disrupted 3D ECM scaffolds, while N. lovaniensis had a minimal effect. Collectively, these results indicate a distinction in adhesion to, and invasion of, ECM proteins between N. fowleri and N. lovaniensis.

Reactive oxygen species-dependent necroptosis in Jurkat T cells induced by pathogenic free-living Naegleria fowleri

Naegleria fowleri, a free-living amoeba, is the causative pathogen of primary amoebic meningoencephalitis in humans and experimental mice. N. fowleri is capable of destroying tissues and host cells through lytic necrosis. However, the mechanism by which N. fowleri induces host cell death is unknown. Electron microscopy indicated that incubation of Jurkat T cells with N. fowleri trophozoites induced necrotic morphology of the Jurkat T cells. N. fowleri also induced cytoskeletal protein cleavage, extensive poly (ADP-ribose) polymerase hydrolysis and lactate dehydrogenase (LDH) release. Although no activation of caspase-3 was observed in Jurkat T cells co-incubated with amoebae, intracellular reactive oxygen species (ROS) were strongly generated by NADPH oxidase (NOX). Pretreating cells with necroptosis inhibitor necrostatin-1 or NOX inhibitor diphenyleneiodonium chloride (DPI) strongly inhibited amoeba-induced ROS generation and Jurkat cell death, whereas pan-caspase inhibitor z-VAD-fmk did not. N. fowleri-derived secretory products (NfSP) strongly induced intracellular ROS generation and cell death. Necroptotic effects of NfSP were effectively inhibited by pretreating NfSP with proteinase K. Moreover, NfSP-induced LDH release and intracellular ROS accumulation were inhibited by pretreating Jurkat T cells with DPI or necrostatin-1. These results suggest that N. fowleri induces ROS-dependent necroptosis in Jurkat T cells.

The Nf-actin gene is an important factor for food-cup formation and cytotoxicity of pathogenic Naegleria fowleri

Naegleria fowleri destroys target cells by trogocytosis, a phagocytosis mechanism, and a process of piecemeal ingestion of target cells by food-cups. Phagocytosis is an actin-dependent process that involves polymerization of monomeric G-actin into filamentous F-actin. However, despite the numerous studies concerning phagocytosis, its role in the N. fowleri food-cup formation related with trogocytosis has been poorly reported. In this study, we cloned and characterized an Nf-actin gene to elucidate the role of Nf-actin gene in N. fowleri pathogenesis. The Nf-actin gene is composed of 1,128-bp and produced a 54.1-kDa recombinant protein (Nf-actin). The sequence identity was 82% with nonpathogenic Naegleria gruberi but has no sequence identity with other mammals or human actin gene. Anti-Nf-actin polyclonal antibody was produced in BALB/c mice immunized with recombinant Nf-actin. The Nf-actin was localized on the cytoplasm, pseudopodia, and especially, food-cup structure (amoebastome) in N. fowleri trophozoites using immunofluorescence assay. When N. fowleri co-cultured with Chinese hamster ovary cells, Nf-actin was observed to localize around on phagocytic food-cups. We also observed that N. fowleri treated with cytochalasin D as actin polymerization inhibitor or transfected with antisense oligomer of Nf-actin gene had shown the reduced ability of food-cup formation and in vitro cytotoxicity. Finally, it suggests that Nf-actin plays an important role in phagocytic activity of pathogenic N. fowleri.

Identification of Naegleria fowleri in warm ground water aquifers

The free-living amoeba Naegleria fowleri was identified as the etiological agent of primary amoebic meningoencephalitis that caused the deaths of two children in Peoria, Arizona, in autumn of 2002. It was suspected that the source of N. fowleri was the domestic water supply, which originates from ground water sources. In this study, ground water from the greater Phoenix Metropolitan area was tested for the presence of N. fowleri using a nested polymerase chain reaction approach. Phylogenetic analyses of 16S rRNA sequences of bacterial populations in the ground water were performed to examine the potential link between the presence of N. fowleri and bacterial groups inhabiting water wells. The results showed the presence of N. fowleri in five out of six wells sampled and in 26.6% of all ground water samples tested. Phylogenetic analyses showed that beta- and gamma-proteobacteria were the dominant bacterial populations present in the ground water. Bacterial community analyses revealed a very diverse community structure in ground water samples testing positive for N. fowleri.

Contact-independent cell death of human microglial cells due to pathogenic Naegleria fowleri trophozoites

Free-living Naegleria fowleri leads to a fatal infection known as primary amebic meningoencephalitis in humans. Previously, the target cell death could be induced by phagocytic activity of N. fowleri as a contact-dependent mechanism. However, in this study we investigated the target cell death under a non-contact system using a tissue-culture insert. The human microglial cells, U87MG cells, co-cultured with N. fowleri trophozoites for 30 min in a non-contact system showed morphological changes such as the cell membrane destruction and a reduction in the number. By fluorescence-activated cell sorter (FACS) analysis, U87MG cells co-cultured with N. fowleri trophozoites in a non-contact system showed a significant increase of apoptotic cells (16%) in comparison with that of the control or N. fowleri lysate. When U87MG cells were co-cultured with N. fowleri trophozoites in a non-contact system for 30 min, 2 hr, and 4 hr, the cytotoxicity of amebae against target cells was 40.5, 44.2, and 45.6%, respectively. By contrast, the cytotoxicity of non-pathogenic N. gruberi trophozoites was 10.2, 12.4, and 13.2%, respectively. These results suggest that the molecules released from N. fowleri in a contact-independent manner as well as phagocytosis in a contact-dependent manner may induce the host cell death.

Effect of therapeutic chemical agents in vitro and on experimental meningoencephalitis due to Naegleria fowleri

Naegleria fowleri is a ubiquitous, pathogenic free-living amoeba; it is the most virulent Naegleria species and causes primary amoebic meningoencephalitis (PAME) in laboratory animals and humans. Although amphotericin B is currently the only agent available for the treatment of PAME, it is a very toxic antibiotic and may cause many adverse effects on other organs. In order to find other potentially therapeutic agents for N. fowleri infection, the present study was undertaken to evaluate the in vitro and in vivo efficacies of miltefosine and chlorpromazine against pathogenic N. fowleri. The result showed that the growth of the amoeba was effectively inhibited by treatment with amphotericin B, miltefosine, and chlorpromazine. When N. fowleri trophozoites were treated with amphotericin B, miltefosine, and chlorpromazine, the MICs of the drug were 0.78, 25, and 12.5 microg/ml, respectively, on day 2. In experimental meningoencephalitis of mice that is caused by N. fowleri, the survival rates of mice treated with amphotericin B, miltefosine, and chlorpromazine were 40, 55, and 75%, respectively, during 1 month. The average mean time to death for the amphotericin B, miltefosine, and chlorpromazine treatments was 17.9 days. In this study, the effect of drugs was found to be optimal when 20 mg/kg was administered three times on days 3, 7, and 11. Finally, chlorpromazine had the best therapeutic activity against N. fowleri in vitro and in vivo. Therefore, it may be a more useful therapeutic agent for the treatment of PAME than amphotericin B.

[Isolation and identification of potentially pathogenic free-living amoebae in samples from environments in a public hospital in the city of Porto Alegre, Rio Grande do Sul]

A study on the presence of free-living amoebae in a public hospital was developed in the city of Porto Alegre, State of Rio Grande do Sul. Dust and biofilms were collected using sterile swabs that had been prepared for this study, from 15 hospital environments, including the intensive care center, pediatric intensive care unit, kitchen, emergency room, outpatient surgical center, clinical surgical center, water storage tanks, taps and six drinking fountains for general use, every month from July 2004 to March 2005. The FLAs were isolated by culturing, using non-nutrient agar medium with the addition of heat-killed Escherichia coli. The protozoa were identified by morphological observation of cysts and trophozoites, in accordance with Page's morphological criteria (1988). Among the 135 samples collected from the 15 environments, 47 (35%) were positive for FLAs. Of these, thirty-four percent presented morphological characteristics particular to the genus Acanthamoeba.

Primary amebic meningoencephalitis: a silent killer

One week after swimming in a man-made lake, a 9-year-old boy presented to the emergency department with headache, vomiting and lethargy. He had neck pain upon flexion and was unable to stand or walk. Cerebrospinal fluid examination revealed trophozoite and diflagellate forms consistent with Naegleria fowleri, an ameba species known to cause primary amebic meningoencephalitis. Despite aggressive management with amphotericin B and rifampin, he died 2 days later. This case report describes the clinical presentation, diagnostic findings and management of this uncommon but lethal entity.

Neuroparasitic infections: cestodes, trematodes, and protozoans

Parasitic infection of the nervous system can produce a variety of symptoms and signs. Because symptoms of infection are often mild or nonspecific, diagnosis can be difficult. Familiarity with basic epidemiological characteristics and distinguishing radiographic findings can increase the likelihood of detection and proper treatment of parasitic infection of the nervous system. This article discusses the clinical presentation, diagnosis, and treatment for some of the more common infections of the nervous system caused by cestodes, trematodes and protozoans: Echinococcus spp., Spirometra spp. (sparganosis), Paragonimus spp., Schistosoma spp., Trypanosoma spp., Naegleria fowlerii, Acanthamoeba histolytica, and Balamuthia mandrillaris.

In vitro and in vivo activity of 5-fluorocytosine on Acanthamoeba

The results of our studies indicated that the avirulent Neff strain of Acanthamoeba was more susceptible to the activity of the anti-metabolite 5-fluorocytosine (5-FC) than was the virulent A-1 strain or a mouse brain reisolate of this strain, designated A-3. Results of competition experiments in which cultures were exposed simultaneously to 5-FC and either uracil, thymidine, or both uracil and thymidine demonstrated that the drug was directed against both deoxyribonucleic acid and ribonucleic acid in the avirulent strain, whereas ribonucleic acid was mainly affected in the virulent amebas. Concentrations >10 mug of 5-FC per ml were amebicidal to the avirulent strain; lower concentrations of the drug, which only affected growth slightly, significantly impaired the capacity of the cells to spontaneously encyst in stationary-phase cultures. On the other hand, the virulent strains were capable of growing in the presence of 5-FC (40 mug/ml) after an initial period of susceptibility. After a few transfers in growth medium lacking the drug, 5-FC-treated virulent amebas exhibited growth parameters typical of untreated cells. However, after successive subcultures in drug-free medium, 5-FC-treated cells lost their resistance and were again susceptible to the drug. This result suggested that the capacity of the cells to develop resistance resulted from a drug-induced mechanism. Spontaneous encystment, which was normally minimal in stationary-phase A-1 or A-3 cultures, was enhanced in A-3 but not A-1 cultures treated with 5-FC (>30 mug/ml). Results obtained from experiments to determine the effectiveness of 5-FC in protecting mice experimentally infected with either A-1 or A-3 amebas indicated that the clinical usefulness of 5-FC may be limited by the capacity of the amebas to develop resistance.

Assessing the risk of primary amoebic meningoencephalitis from swimming in the presence of environmental Naegleria fowleri

Free-living Naegleria fowleri amoebae cause primary amoebic meningoencephalitis (PAM). Because of the apparent conflict between their ubiquity and the rarity of cases observed, we sought to develop a model characterizing the risk of PAM after swimming as a function of the concentration of N. fowleri. The probability of death from PAM as a function of the number of amoebae inhaled is modeled according to results obtained from animals infected with amoeba strains. The calculation of the probability of inhaling one or more amoebae while swimming is based on a double hypothesis: that the distribution of amoebae in the water follows a Poisson distribution and that the mean quantity of water inhaled while swimming is 10 ml. The risk of PAM for a given concentration of amoebae is then obtained by summing the following products: the probability of inhaling n amoebae x the probability of PAM associated with inhaling these n amoebae. We chose the lognormal model to assess the risk of PAM because it yielded the best analysis of the studentized residuals. Nonetheless, the levels of risk thereby obtained cannot be applied to humans without correction, because they are substantially greater than those indicated by available epidemiologic data. The curve was thus adjusted by a factor calculated with the least-squares method. This provides the PAM risk in humans as a function of the N. fowleri concentration in the river. For example, the risk is 8.5 x 10(-8) at a concentration of 10 N. fowleri amoebae per liter.

A light microscopy study of the migration of Naegleria fowleri from the nasal submucosa to the central nervous system during the early stage of primary amebic meningoencephalitis in mice

The migratory pathway of Naegleria fowleri from the nasal submucosa to the central nervous system (CNS) during the early stage of primary amebic meningoencephalitis (PAM) was investigated in mice. Twenty-one-day-old CD-1 mice were inoculated by intranasal instillation of 1 x 10(6) amebas. Animals were divided into 3 groups of 5 and, after being anesthetized, were killed at intervals of 24, 32, and 48 hr postinoculation by transcardial perfusion with formaldehyde, acetic acid, and methanol. The heads were decalcified, divided in the midsagittal plane, and the area of the cribriform plate removed and embedded in paraffin. Serial sections were cut at 8 microm and stained with a combination of celestin blue, Harris' hematoxylin, and acid fuchsin for light microscopy. Focal inflammation and amebas were observed in the submucosal nerve plexus, olfactory nerves penetrating the cribriform plate, and the olfactory bulb of the brain as early as 24 hr postinoculation. The time periods selected assured that the disease process would not obliterate soft tissue structures. Earlier studies used moribund mice in which the inflammation and the number of amebas were overwhelming. The present study provides convincing evidence that amebas gain initial access to the CNS through olfactory nerves within the cribriform plate during the early stages of PAM.

Parasitic infections of the central nervous system in children. Part I: Congenital infections and meningoencephalitis

This review article presents the epidemiology, pathogenesis, clinical presentation, laboratory and radiologic findings, and treatment of parasitic infections of the central nervous system in children. Some obscure parasitic infections are included. To assist the clinician faced with a specific case, infections are categorized first by predominant clinical manifestations: congenital disease, meningoencephalitis, focal lesions, and disseminated multisystem disease. Within the clinical categories, parasites are grouped according to the geographic area where most human infections occur. Congenital infections and those that present most frequently as meningoencephalitis are discussed in this part of the review.

Detection of Naegleria fowleri cysts in environmental samples by using a DNA probe

In this study we tried to detect DNA Naegleria fowleri in artificially contaminated environmental samples, with or without sediments, containing 10(4) cysts of this pathogenic amoeba. We used two assays to extract DNA from samples: first, direct DNA extraction, which gave positive results only for water samples without sediment; second, DNA extraction after sample incubation on agar plates, which allowed us to remove amoeba growing out of the sediments, and which gave positive results for all samples, even those initially with sediments (5, 500 or 500 mg). Thus, this molecular identification appears as a powerful tool to investigate N. fowleri growth in environmental samples.

Differentiation of Naegleria fowleri and other Naegleriae by polymerase chain reaction and hybridization methods

In order to detect and identify Naegleria fowleri strains an assay based on the Polymerase Chain Reaction (PCR) was evaluated. The amplified DNA fragments were detected by gel electrophoresis and ethidium bromide staining, followed by Southern blot hybridization with an internal digoxigenin-labeled probe. A set of primers (B1B2) which flank a 678-bp region within a virulence-associated gene, allowed for the highly specific identification of N. fowleri, since Naegleriae (N. lovaniensis, N. australiensis, N. gruberi, N. andersoni and N. jadini) and other Protozoa did not react. These primers did not detect amplification products from various organisms: Gram-positive bacteria, Gram-negative bacteria, algae, yeasts and human DNA. Whereas a second set of primers (A1A2), which flank a different sequence, detected various Naegleriae and Acanthamoebae strains. After 40 amplification cycles, the limit of detection was a single cell (cyst or trophozoite). Thus, the PCR appears to be a rapid and powerful tool for identification and detection of N. fowleri.

Antagonistic action of the bacterium Bacillus licheniformis M-4 toward the amoeba Naegleria fowleri

Free-living amoebae belonging to the species Naegleria fowleri are known to be the etiological agents for a form of fulminant meningoencephalitis that is generally fatal (primary amoebic meningoencephalitis). In a broad bacterial screening from soil and water we have isolated three strains (M-4, D-13 and A-12) belonging to the species Bacillus licheniformis that have remarkable amoebicidal activity against Naegleria sp. and also against different Gram-positive and Gram-negative bacteria. Physical-chemical characteristics, partial purification and biological activities of a substance produced by the M-4 strain have been investigated. This substance (m-4) is stable at high temperature (up to 100 degrees C) and extremes of pH (2.5-9.5) and also at -20 degrees C for months. Its production is greatly influenced by oxygenation of the cultures and is probably related to the sporulation process of the bacterium. Scanning electron microscope observations reveal that amoebae are lysed after a few minutes contact with m-4.

[Natural killer cell activity in Naegleria fowleri infected mice]

The natural killer (NK) cell activity of splenocytes and recycling capacity of NK cells were observed by combining the 51Cr-release cytotoxicity assay and single cell cytotoxicity assay against YAC-1. The ICR mice were infected intranasally with Naegleria fowleri, that is a pathogenic free-living amoeba. The mice infected with 1 x 10(5) trophozoites showed mortality rate of 76.7% and mean survival time of 12.9 days. The cytotoxic activity of NK cells in infected mice was significantly higher than that of non-infected mice during the period between 12 hours and day 3 after infection, and highest on day 1. The target-binding capacity of NK cells in infected mice was not different from that of non-infected ones. Maximal killing potential and maximal recycling capacity were remarkably increased in infected mice as compared with the control. The results obtained in this observation indicated that elevated NK cell activity in mice infected with N. fowleri was not due to target-binding capacity of NK cells but due to the increased activity of NK cells and increased recycling capacity of individual NK cells.

Differentiation of Naegleria fowleri from Acanthamoeba species by using monoclonal antibodies and flow cytometry

Monoclonal antibodies to Naegleria fowleri and Acanthamoeba polyphaga were analyzed by enzyme-linked immunosorbent assay, indirect immunofluorescence microscopy, and fluorescence flow cytometry to assess specificity and cross-reactivity with axenically cultured N. fowleri and Acanthamoeba spp. Four monoclonal antibodies to N. fowleri were specific for N. fowleri and had no reactivity to A. polyphaga. Similarly, four monoclonal antibodies to A. polyphaga did not react with N. fowleri. Two of the four monoclonal antibodies to A. polyphaga did not react with other Acanthamoeba spp. tested, while two of the antibodies demonstrated a high degree of cross-reactivity with a putative Acanthamoeba castellanii strain by immunofluorescence microscopy; this was confirmed by fluorescence flow cytometry for one of the antibodies. These monoclonal antibodies were used to identify Acanthamoeba trophozoites in infected brain sections of a patient who died of suspected Acanthamoeba-caused granulomatous amoebic encephalitis, demonstrating potential utility in the direct identification of N. fowleri and Acanthamoeba spp. in clinical specimens.

[Cell-mediated immunity in mice infected with Acanthamoeba culbertsoni]

Observations were made on the differences of cell-mediated responses in mice of three infection groups differently scheduled in their severity with pathogenic Acanthamoeba culbertsoni. Infections were done by dropping 5 microliters saline suspension containing 3 x 10(3), 1 x 10(4), or 1 x 10(5) trophozoites, respectively. Amoebae were cultured axenically in CGV medium and inoculated into the right nasal cavity of C3H/HeJ mice aging around 6-8 weeks, under the anesthesia by intraperitoneal injection of secobarbital. Delayed type hypersensitivity (DTH) responses in footpad and blastogenic responses of mouse spleen cells using (3H)-thymidine and the serum antibody titer were measured up to day 14 after infection, and natural killer cell activities were measured up to day 5 after infection. The results obtained in this study were as follows: 1. The mice infected with 3 x 10(3) trophozoites showed mortality rate of 17%, and 34% in the mice infected with 1 x 10(4) trophozoites and 65% with 1 x 10(5) trophozoites. 2. In regard to DTH responses in all experimental groups, the level increased on day 7 and declined on day 14 after infection, but their differences could not be noted between infected and control groups. 3. The blastogenic responses of splenocytes treated with amoeba lysates and lipopolysaccharides (LPS) showed no difference from the control group. The blastogenic responses of splenocytes treated with concanavalin A were declined significantly in the experimental group as compared with the control group, but the blastogenic responses of splenocytes treated with polyinosinic acid were not different from the control group. There was also no difference among three infected groups. 4. The cytotoxic activity of the natural killer cells was activated on day 1 after infection and declined to the level of control group on day 2 in all experimental groups. On day 5 after infection, the natural killer cell cytotoxicity was significantly suppressed as compared with the control groups. 5. The serum antibody titers of the infected mice increased after day 7, but there was no statistical difference between the three infected groups. In summary of the results, there was no difference in cell-mediated immune responses of three experimental groups scheduled with different infection intensities. But there was a significant difference in cell-mediated immune responses between infected and control mice. It is considered that cell-mediated immune responses should be involved in murine model infected with A. culbertsoni.

Effect of thermal additions on the density and distribution of thermophilic amoebae and pathogenic Naegleria fowleri in a newly created cooling lake

Pathogenic Naegleria fowleri is the causative agent of fatal human amoebic meningoencephalitis. The protozoan is ubiquitous in nature, and its presence is enhanced by thermal additions. In this investigation, water and sediments from a newly created cooling lake were quantitatively analyzed for the presence of thermophilic amoebae, thermophilic Naegleria spp., and the pathogen Naegleria fowleri. During periods of thermal additions, the concentrations of thermophilic amoebae and thermophilic Naegleria spp. increased as much as 5 orders of magnitude, and the concentration of the pathogen N. fowleri increased as much as 2 orders of magnitude. Concentrations of amoebae returned to prior thermal perturbation levels within 30 to 60 days after cessation of thermal additions. Increases in the thermophilic amoeba concentrations were noted in Savannah River oxbows downriver from the Savannah River plant discharge streams as compared with oxbows upriver from the discharges. Concentrations of thermophilic amoebae and thermophilic Naegleria spp. correlated significantly with temperature and conductivity. Air samples taken proximal to the lake during periods of thermal addition showed no evidence of thermophilic Naegleria spp. Isoenzyme patterns of the N. fowleri isolated from the cooling lake were identical to patterns of N. fowleri isolated from other sites in the United States and Belgium.

Biology of Naegleria spp

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Granulomatous brain tumor caused by Acanthamoeba. Case report

A case of a previously healthy 7-year-old girl with a left frontoparietal tumor identified as an Acanthamoeba-induced granuloma is reported, and the literature on Acanthamoeba meningoencephalitis is reviewed. Unlike most reported cases, the Acanthamoeba central nervous system infection presented in this girl as a discrete tumor without meningeal involvement or diffuse encephalitis. A favorable outcome was obtained following total excision of the mass and treatment with ketoconazole.

Acanthamoebic keratitis in a healthy Australian man

We report a case of acanthamoebic keratitis that occurred after minor ocular trauma in a healthy 31-year-old man. Multiple microbiological investigations failed to reveal the causative organism, which was identified as Acanthamoeba castellanii only after a corneal graft operation had been performed. A review of previously described cases reveals that this rare ocular infection tends to cause recalcitrant corneal ulcers after minor eye injuries in otherwise healthy individuals.

Primary amebic meningoencephalitis

Primary amebic meningoencephalitis is a disease caused by the free-living amebae of the genera Naegleria or Acanthamoeba. The clinical course may result in death a few days after presentation or it may be insidious, with progressive neurologic deterioration and death after a chronic course. This article describes the organisms involved, the clinical course, pathology, diagnosis, and treatment of the disease.

[Effect of splenectomy on development of primary amoebic meningoencephalitis]

To elucidate the effect of splenectomy on the development of experimental primary amoebic meningoencephalitis in mice, the death rate and survival time of mice infected intranasally with Naegleria fowleri trophozoites 5 x 10(4) cultivated in CGVS medium were compared according to the age when splenectomy was done, and post-operation until experimental infection. Immunodiffusion was undergone to detect the presence of serum antibody due to N. fowleri infection in mice. Polyacrylamide gel electrophoresis was done to compare the protein fractions of mouse serum in each experimental groups. In experiment I, splenectomy was done 3 weeks and infection 4 weeks after birth, the death rate of control, sham operated and splenectomized group were 100 percent, 85 percent and 95 percent, and the mean survival time after infection 7.3 days, 7.5 days and 7.8 days, respectively. In experiment II, splenectomy was undergone 3 weeks and infection 6 weeks after birth, the death rate of control, sham operated and splenectomized group were 95 percent, 95 percent and 95 percent, and the mean survival time after infection 12.1 days, 11.5 days and 11.5 days, respectively. In experiment III, splenectomy was done 5 weeks and infection 6 weeks after birth, the death rate of control, sham operated and splenectomized group were 95 percent, 90 percent and 95 percent, and the mean survival time after infection 8.1 days, 8.3 days and 8.5 days, respectively. By Ouchterlony immunodiffusion, anti-N. fowleri antibody in the serum of mouse with primary amoebic meningoencephalitis was detected against a N. fowleri antigen, which was prepared by ultrasonication of N. fowleri trophozoites, each reacting two lines of precipitation. The patterns of serum fractions by polyacrylamide gel electrophoresis were different between control and sham operated groups from splenectomized group in fraction II, III and V, the sera of which were collected after N. fowleri infection. This results may be summarized as that splenectomy has no effect on the development of primary amoebic meningoencephalitis in mice.

[Effect of prednisolone treatment on the experimental inducement of primary amoebic meningoencephalitis]

Present study aimed to elucidate the immunosuppressive effect of prednisolone on Naegleria fowleri infection in mice. N. fowleri was cultured in CGVS medium (Willert and Le Ray, 1973). White female mice, weighing about 18 g, used for experiments were divided into five groups; untreated control group, prednisolone treated groups (before, during and after infection), and only prednisolone treated group. In the prednisolone treated group, the hormone was injected intramuscularly 5 doses of 10 mg/kg every other day. According to designated time of treatment, each mouse was challenged with 1 x 10(5) N. fowleri intranasally. Changes of body weights, clinical manifestations and number of dead mouse were observed. Brain and lung tissues of dead mice were cultured in the non-nutrient agar (Kasprzak and Mazur, 1972), or stained with hematoxylin-eosin for the examination of histopathological changes. Results of the experiment are summarized as follows: Mortality among the prednisolone treated groups was higher than that in untreated control group, and among the treated groups, the pretreated group showed shorter survival time. Body weights among untreated control mice showed no significant increase, however, treated groups of mice showed the decrease during the administration and recovery of the weights were observed at 2 to 3 days after the completion of treatment. In the treated control groups, the infected mice began to show the pathologic findings 5 days after infection while the untreated mice began to show the findings 8 days after infection. Tissue damages in brain and lung occurred due to virulence of amoeba were more severe among treated mice than that in untreated control group. The above mentioned results suggest that the treatment with prednisolone weaken the resistance of mice against N. fowleri infection, and probably induce more severe primary amoebic meningoencephalitis. Especially severe pathological findings were shown in pre-treated group, compared with untreated group.

Pathogenic and free-living protozoa cultured from the nasopharyngeal and oral regions of dental patients

Protozoa of nose, mouth, and pharynx of 30 randomly chosen female caries patients at an odontological clinic of the National Autonomous University of Mexico, were surveyed by culture from swabs. Culture tubes of swabs from each patient were observed every other day during 5 weeks. Pathogenic protozoa found included Entamoeba histolytica Schaudinn, 1903; Naegleria fowleri Carter, 1970; Acanthamoeba castelanii Douglas, 1930; Acanthamoeba culbertsoni Singh & Das, 1970; and Balantidium coli (Malmsten, 1857) Stein, 1862. This isolation of pathogens suggests that healthy patients may be healthy carriers of cysts of protozoa, mainly amoebae, responsible for several diseases, including primary amoebic meningoencephalitis. Small pathogenic free-living amoebae have not been isolated before from females in Mexico. Many species of free-living protozoa were also cultured from swabs from the patients.

[Changes In The Pathogenicity Of Naegleria Fowleri By Several Brain Passage In Mice]

The pathogenicity of free-living amoeba, Naegleria fowleri, is influenced according to the strain, cultural condition and host (Culbertson et al., 1968; Carter, 1970; Wong et al., 1975). Phillips (1973) demonstrated that Entamoeba histolytica became avirulent after more than 2 year maintenance in axenic culture in vitro. This study was carried out to compare the difference in pathogenicity between two strains of N. fowleri, one of a prolonged maintenance in axenic medium and the other one obtained by serial brain passage in mice. The 0 strain was that N. fowleri had cultivated axenically more than 7 years in CGVS medium. The 2-1 strain was obtained from the brain of mouse inoculated intranasally with a strain, which was from the mouse brain infected with 0 strain, and cultured for 15 weeks until the beginning of this experiment. White male mice weighing 18-22 g were used. Mice were anesthetized by an intraperitoneal injection of about 1 mg secobarbital, and inoculated intranasally with 10 x 10(4) live N. fowleri trophozoites in a 5 microliter cell suspension. Sluggish behaviour, nervousness, rotation and leg paralysis were developed earlier and more frequently in the 2-1 experimental group than the control 0 group. Pathological changes such as inflammatory and necrotic lesion were observed in the olfactory and anterior portion of brain, and these changes were more extensive in the 2-1 group. The edematous and inflammatory changes in lung were demonstrated in mice died after 13th day post-inoculation. The experimental mice of 2-1 group began to die suddenly from 7th day post-inoculation, and the survival time in 2-1 group mice was shorter than 0 group mice. The typical primary amoebic meningoencephalitis was developed in the mice inoculated intranasally with N. fowleri. The prolonged maintenance of N. fowleri amoebae in axenic CGVS medium was observed to have lost their original pathogenicity for mice, but their pathogenicity was restored by serial brain passage in mice.

A survey of pathogenic and free-living amoebae inhabiting swimming pool water in Mexico City

A survey of pathogenic and free-living amoebae in swimming pool waters of Mexico City was performed. Among the organisms isolated those which have public health importance were Naegleria fowleri Carter and Acanthamoeba castellanii Douglas. Amoebae of the genera Acanthamoeba, Naegleria, and Vahlkampfia were recovered in their cystic stage while those specimens of the genera Amoeba, Entamoeba, Thecamoeba, and Vanella were recovered only in their trophic stage during this study. Amoebae were concentrated through filtration procedures and subsequently cultured in different culture media. Nonpathogenic amoebae also isolated by culture included: Amoeba proteus (Pallas) Leidy, Amoeba striata Penard, Paratetramitus jugosus Page, Acanthamoeba astronyxis Ray and Hayes, Vahlkampfia avara Page, Vahlkampfia inornata Page, Thecamoeba verrucosa Ehrenberg, and Vanella mira Schaeffer. Trophozoites of Entamoeba gingivalis Gros, were also recovered, both directly and by culture. Most commonly found were amoebae of the species Naegleria gruberi Schardinger (59.02%), N. fowleri (16.77%), and A. castellanii (7.64%). Least-frequently found amoebae belonged to the species Thecamoeba verrucosa (0.12%). All isolated strains of N. fowleri and A. castellanii were thermophilic at 45 and 40 degrees C, respectively, and also pathogenic when inoculated into white mice. More populated by amoebae were those swimming pools of the indoor type with an inner side garden. It was also shown that the free residual chloride values of 0.50 to 1.5 mg/liter, ordinarily used in pool waters, are not adequate for elimination of amoebae.