Naegleria (sp.) identified in amebic encephalitis

Differential Growth Rates and In Vitro Drug Susceptibility to Currently Used Drugs for Multiple Isolates of Naegleria fowleri

The free-living amoeba Naegleria fowleri, which typically dwells within warm, freshwater environments, can opportunistically cause primary amoebic meningoencephalitis (PAM), a disease with a mortality rate of >97%. The lack of positive treatment outcomes for PAM has prompted the discovery and development of more effective therapeutics, yet most studies utilize only one or two clinical isolates. The inability to assess possible heterogenic responses to drugs among isolates from various geographical regions hinders progress in the discovery of more effective drugs. Here, we conducted drug efficacy and growth rate determinations for 11 different clinical isolates by applying a previously developed CellTiter-Glo 2.0 screening technique and flow cytometry. We found significant differences in the susceptibilities of these isolates to 7 of 8 drugs tested, all of which make up the cocktail that is recommended to physicians by the U.S. Centers for Disease Control and Prevention. We also discovered significant variances in growth rates among isolates, which draws attention to the differences among the amoeba isolates collected from different patients. Our results demonstrate the need for additional clinical isolates of various genotypes in drug assays and highlight the necessity for more targeted therapeutics with universal efficacy across N. fowleri isolates. Our data establish a needed baseline for drug susceptibility among clinical isolates and provide a segue for future combination therapy studies as well as research related to phenotypic or genetic differences that could shed light on mechanisms of action or predispositions to specific drugs.

IMPORTANCENaegleria fowleri, also known as the brain-eating amoeba, is ubiquitous in warm freshwater and is an opportunistic pathogen that causes primary amoebic meningoencephalitis. Although few cases are described each year, the disease has a case fatality rate of >97%. In most laboratory studies of this organism, only one or two well-adapted lab strains are used; therefore, there is a lack of data to discern if there are major differences in potency of currently used drugs for multiple strains and genotypes of the amoeba. In this study, we found significant differences in the susceptibilities of 11 N. fowleri isolates to 7 of the 8 drugs currently used to treat the disease. The data from this study provide a baseline of drug susceptibility among clinical isolates and suggest that new drugs should be tested on a larger number of isolates in the future.

Naegleria fowleri after 50 years: is it a neglected pathogen?

It has been 50 years since the first case of primary amoebic meningoencephalitis (PAM), an acute and rapidly fatal disease of the central nervous system (CNS), was reported in Australia. It is now known that the aetiological agent of PAM is Naegleria fowleri, an amoeba that is commonly known as 'the brain-eating amoeba'. N. fowleri infects humans of different ages who are in contact with water contaminated with this micro-organism. N. fowleri is distributed worldwide and is found growing in bodies of freshwater in tropical and subtropical environments. The number of PAM cases has recently increased, and the rate of recovery from PAM has been estimated at only 5 %. Amphotericin B has been used to treat patients with PAM. However, it is important to note that there is no specific treatment for PAM. Moreover, this amoeba is considered a neglected micro-organism. Researchers have exerted great effort to design effective drugs to treat PAM and to understand the pathogenesis of PAM over the past 50 years, such as its pathology, molecular and cellular biology, diagnosis and prevention, and its biological implications, including its pathogenic genotypes, its distribution and its ecology. Given the rapid progression of PAM and its high mortality rate, it is important that investigations continue and that researchers collaborate to gain better understanding of the pathogenesis of this disease and, consequently, to improve the diagnosis and treatment of this devastating infection of the CNS.

Acanthamoeba spp. as agents of disease in humans

Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and water environments. However, these amebae can also act as opportunistic as well as nonopportunistic pathogens. They are the causative agents of granulomatous amebic encephalitis and amebic keratitis and have been associated with cutaneous lesions and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate against Acanthamoeba have not been well characterized, but it has been proposed that both innate and acquired immunity play a role. The ameba's life cycle includes an active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria, yeast, and algae. However, both trophozoites and cysts can retain viable bacteria and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent dye staining, PCR, and analysis of DNA sequence variation also have been employed for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed results. However, chlorhexidine gluconate, alone or in combination with propamidene isethionate, is effective in some patients. Furthermore, effective treatment is complicated since patients may present with underlying disease and Acanthamoeba infection may not be recognized. Since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.

[Immunological approach for classification of free-living amoeba in Korea]

Acanthamoeba spp., free-living amoebae inhabited in moist soil, pond, freshwater, sewage, atmosphere and swimming pool, may be causative protozoa of the fatal primary amoebic meningoencephalitis in experimental animals and humans. In this study, Acanthamoeba spp., including Acanthamoeba sp. YM-4 (isolated strain from Korea) had been compared by the two-dimensional electrophoresis and hybridoma technique as well as the difference of morphological characteristics. Trophozoite of Acanthamoeba sp. YM-4 is usually uninucleate and show the hyaline filamentous projections (acanthopoda). No flagellate stage observed. Cysts have two walls, the outer wall is nearly circular, but inner wall is oval or some irregular. As results of SDS-PAGE for lysate of Acanthamoeba sp. YM-4, 16 major protein fractions are similar to those of A. culbertsoni, but different to A. royreba and A. polyphaga. Findings of two-dimensional electrophoretic patterns of Acanthamoeba sp. YM-4 are almost same to those of A. culbertsoni, The isotype of monoclonal antibodies produced from McAY 6, McAY 7, McAY 8, McAY 13 and McAY 16 clones were IgG1, and McAY 10 and McAY 11 clones were IgM. As results of the cross-reactivity among various amoebae using ELISA with monoclonal antibodies, McAY 7 monoclonal antibody (molecular weight 43 kDa by EITB) was only reacted with Acanthamoeba sp. YM-4, but McAY 6 and McAY 10 monoclonal antibodies were reacted to A. culbertsoni as well as Acanthamoeba sp. YM-4.

[The protective effects of monoclonal antibodies in mice from Naegleria fowleri infection]

Protective effects of monoclonal antibodies against N. fowleri were comparatively studied. BALB/c mice were treated with two types of monoclonal antibodies, Nf 2 and Nf 154, before and after the infection with N. fowleri. The mortality and mean survival times were then compared. Also, direct effect of the monoclonal antibodies on the N. fowleri trophozoites in vitro were observed. In vitro protective effects of the monoclonal antibodies were also studied in cells infected with N. fowleri. The observed results are summarized as follows: 1. Among mice pretreated twice before the infection with monoclonal antibody Nf 2(McAb Nf 2), only 15.8% were killed, and the mean survival time was 17.7 days. This was not much different from the mice pretreated once, as the mortality and mean survival time were 16.7% and 17 days. Those effects were compatible with monoclonal antibody Nf 154(McAb Nf 154). The above findings contrast with the mortality and mean survival time of the control mice, which were 22.7% and 14.6 days respectively. 2. Mice which received twice the McAb Nf 2 following N. fowleri infection incurred a 19.4% mortality rate with 13.6 days survival time; 17.9% and 15.8 days with on time administration, in contrast to the 25% and 14.6 days in the control group. 3. Marked agglutination effect of McAb Nf 2 or McAb Nf 154 were observed on N. fowleri trophozoites. 4. When N. fowleri trophozoites were treated with McAb Nf 2 or McAb Nf 154 combined with comments, the proliferation rate was more significantly suppressed than in that the control. 5. N. fowleri trophozoites treated with McAb Nf 2 or McAb Nf 154 showed an increased number of swollen mitochondria, disfigured cisternae, lipid droplets, and osmiophilic granules in the cytoplasm. 6. A remarkable protective effect of monoclonal antibodies was noticed in CHO cells infected with N. fowleri. More than 90.6% of the infected CHO cells survived, contrasted with 27% of untreated cells. The overall results in this study suggest that N. fowleri treated with monoclonal antibodies against N. fowleri reduce the mortality and prolong the survival time of the mice when the antibodies are administered before the infection. The protective effect of the monoclonal antibodies is surmised being caused by agglutination of the trophozoites.

Free-living amoebae: pathogenicity and immunity

Free-living amoebae causes three well-defined disease entities: (i) primary amoebic meningoencephalitis, caused by Naegleria fowleri, (ii) granulomatous amoebic encephalitis and (iii) chronic amoebic keratitis, caused by species of Acanthamoeba. Both Naegleria infections and chronic amoebic keratitis occur in healthy individuals while granulomatous amoebic encephalitis is often associated with patients with acquired immunodeficiencies. The different pathogenic behaviour of these organisms is associated with differences in life cycle, amoeboidal locomotion, enzyme composition (such as phospholipase A), and cytotoxins, as well as natural host immunity. Immunity against these amoebae (whether acquired or natural) involves a combination of complement, antibody and cell-mediated immunity. Evidence suggests that the major mechanisms of immunity against these amoebae is activation of phagocytic cells, especially neutrophils, by lymphokines and opsonization of the amoebae by antibody which promote an antibody dependent cellular destruction of the organism.

Pathogenic free-living amoebae

Studies on pathogenic free-living amoebae performed in Korea were briefly reviewed. One strain of Naegleria fowleri was isolated from the sewage, and 3 strains of Acanthamoeba culbertsoni from a reservoir and the gill of fish. They were identified by morphological characteristics. Three strains among the 4 were experimentally proved pathogenic to cause primary amoebic meningoencephalitis in mice. The virulence of N. fowleri depended upon various factors such as strain, weight and sex of mice, and number of the inoculated amoebae. A. culbertsoni was found to retain cytolytic activities which were related to the pathogenicity. Also these amoebae were demonstrated to harbour the activities of acid phosphatase, peroxidase and ATPase. There is one case record of systemic Acanthamoeba infection in Korea, proved at autopsy. Cellular or humoral responses to these amoebae have been studied in vitro or in vivo. Immunization could reduce the mortality of experimentally infected mice.

[A comparative study on hydrolase activities in Acanthamoeba culbertsoni and A. royreba]

Specific or non-specific cytolytic processes of free-living amoebae causing meningoencephalitis have been emphasized and the cytolytic ability related to hydrolases in Entamoeba sp. and Naegleria sp. has also been reported since the latter half of 1970's. However, no information on hydrolase activities in Acanthamoeba sp. is available. Hydrolases in Acanthamoeba culbertsoni, a pathogenic species of free-living amoebae, were assayed and compared with those in a non-pathogenic species, A. royreba. Pathogenicity of these two species was confirmed through experimental infection to BALB/c mice. Hydrolase activities and cytotoxic effects between pathogenic and non-pathogenic species were compared in the trophozoites cultured in CGV media and in CHO cell line, respectively. The results are summarized as follows: The mice infected with A. culbertsoni were all dead 15 days after nasal inoculation, and the mean survival time was 8.5 days. Also the mice infected with this pathogenic species mani fested typical meningoencephalitis, whereas the mice infected with A. royreba did not. Hydrolases detected both in the cell extracts and culture media were acid phosphatase, beta-N-acetyl galactosaminidase, beta-N-acetyl glucosaminidase, alpha-mannosidase, neutral proteinase and acid proteinase, all of which were detected with remarkably higher rate in A.culbertsoni than in A. royreba. A. culbertsoni revealed strong cytotoxicity for the target CHO cells, whereas A. royreba did not show any specific cytotoxicity. About 80% of the target cells mixed with A. culbertsoni were dead 48 hours after cultivation, and more than 95% of the target cells were dead 72 hours after cultivation. Hydrolase activities in A. culbertsoni cultured with the target cell line were assayed according to the culture time. The activities of acid phosphatase, beta-N-acetyl glucosaminidase, beta-N-acetyl glucosaminidase, alpha-mannosidase and acid proteinase in this pathogenic amoeba were detected higher in amoeba extracts than in culture media up to 120 hours after cultivation, but after 120 hours of cultivation those activities were detected higher in culture media than in the amoeba lysates. Neutral proteinase activity in A. culbertsoni increased more in EBSS medium than in the lysate specimens although the activity in the extracts was generally steady according to the cultivation time. Summarizing the above results, it is concluded that there were differences in hydrolase activities between pathogenic A. culbertsoni and non-pathogenic A. royreba, and that some hydrolase activities were detected remarkably higher in A. culbertsoni which revealed strong cytotoxicity to the target CHO cell line.

Biology of Naegleria spp

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Seasonal distribution of thermotolerant free-living amoebae. I. Willard's Pond

A quantitative study of the seasonal distribution of thermotolerant (37 degrees C and 45 degrees C), small free-living amoebae (FLA) was conducted in Willard's Pond, a warm, monomictic lake in the Piedmont region of South Carolina. Correlation of physical and chemical parameters with the seasonal distribution was facilitated by partitioning the aquatic ecosystem into benthic, planktonic, and neustonic habitats. Population densities of FLA peaked in late summer in each habitat; however, species composition varied between habitats. Littoral sediment appeared to be the major habitat for FLA, with peaks in populations of Acanthamoeba and Naegleria in August, Hartmannella in July, and Vahlkampfia in May. Populations in profundal sediment underwent dramatic seasonal shifts, apparently in response to the seasonal chemical changes in the hypolimnion. Acanthamoeba was most prevalent in late summer, representing as much as 82% of the FLA in profundal sediment. Distribution patterns and species composition of FLA from surface water were similar to those from littoral sediment; however, a greater percentage of Naegleria was found in surface water. Numerous FLA were isolated from the neustonic community (surface film), and the number of FLA isolated in the surface film at the deep water station was found to be significantly (P less than 0.05) greater than the number from subsurface (5-10 cm) samples. In the water column, FLA populations consistently were highest in the detrital layer, which persisted at a depth of 3.0-3.4 m throughout the summer period. The large percentage of Naegleria contributing to FLA in the detrital layer suggests that Naegleria amoeboflagellates sink through the layer, flagellate, and swim back up, such migrations possibly being triggered by a reduction of nutrients below the layer or by the presence of anoxic, reducing conditions in the hypolimnion. In addition, weather events were found to play a major role in the redistribution of FLA between various habitats in the aquatic ecosystem, with such changes probably due to resuspension of FLA from littoral sediment by wind action and input from the watershed via runoff.

[Protective immunity against Naegleria meningoencephalitis in mice]

This study is to verify the protective ability against experimental Naegleria meningoencephalitis by immunization with Naegleria fowleri in mice. Naegleria fowleri, strain 0359, and Naegleria gruberi, strain EGB, were used in this study, and cultured in CGVS medium axenically. Inbred BALB/c mice, weighing about 20g, were immunized by three intraperitoneal injection of 1 x 10(6) N. fowleri trophozoites at the interval of one week. This N. fowleri trophozoites antigen was fixed with 5 percent formaldehyde. N. fowleri trophozoites from culture were homogenized with sonicator at 4 degrees C as monitored by phase contrast microscopy, and their membrane and cell content preparations were made for the immunization of mice. Their inoculation dose in volume was equivalent to the 1 x 10(6) trophozoites in each injection for immunization. And N. gruberi trophozoites, which was fixed with 5 percent formaldehyde, were also used for immunization. Mice were inoculated intranasally with 5 x 10(4) N. fowleri trophozoites in a 5 microliter suspension under anesthesia by as intraperitoneal injection of about l mg secobarbiturate. Nervousness, rotation or sluggish behaviour were observed in the mice which were infected with N. fowleri. Necrotic lesion was demonstrated in the anterior portion of brain, especially in the olfactory lobe. The inflammatory cell infiltration with numerous N. fowleri trophozoites was noticed. This pathological changes were more extensive in the control than in the experimental groups. Mice were dead due to experimental primary amoebic meningoencephalitis that developed between 8 days and 23 days after inoculation. Mortality rate of the mice was low in the immunized experimental group. Mean survival time, which is the survival duration of mice from the infection to death, was prolonged significantly in the immunized mice except in the mice immunized with N. fowleri membrane. Even in the mice immunized with N. gruberi, survival time was delayed. In summary, the effectiveness of immunization is demonstrated in terms of protective immunity against Naegleria meningoencephalitis in mice.

[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.

[Experimental meningoencephalitis by Naegleria fowleri in mice]

Experimentally, primary amoebic meningoencephalitis (PAM) is induced by Naegleria fowleri in mouse and development of PAM may be influenced by the strain, weight and sex of mouse, and inoculum size of N. fowleri trophozoite. In this paper, the effect of these factors on PAM development of mouse was studied. N. fowleri trophozoites, strain 0359, were introduced into mouse intranasally under secobarbital anesthesia (0.05 mg/g). PAM was developed more frequently in BALB/c mouse than ICR mouse. The survival time of mouse with PAM was influenced by the weight, that is, it was shorter in 15 g mouse than in the heavier groups. No difference was observed on PAM development according to sex. In case of inoculated amoeba, PAM incidence of 0.5 x 10(4) was markedly decreased.

[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.

Naegleria australiensis: experimental meningoencephalitis in mice

Naegleria australiensis was recently described as a new species of free-living amoeba pathogenic for mice. Infections of human brain by the free-living amoebae N. fowleri and Acanthamoeba spp. are well known. We here describe the clinicopathological features of experimental infection of the central nervous system of mice by N. australiensis. Weanling mice were inoculated intranasally and intracerebrally. The involvement of the nasal mucosa, olfactory neuroepithelium and lobes, cerebrum and cerebellum was detected in haematoxylin-eosin stained paraffin-embedded sections. Amoebic trophozoites sparsely located throughout the central nervous system were shown better by the immunoperoxidase method. Cysts were not detected. The histopathological changes differ from those produced by N. fowleri, especially in the degree of severity. They may be confused with those caused by Acanthamoeba spp. which usually produced subacute and chronic encephalitis with a prolonged clinical course.

Primary amoebic meningoencephalitis: fifteen years later

Primary amoebic meningoencephalitis is a fulminant and rapidly fatal diseases which principally affects children and young adults. The causative organism is Naegleria fowleri, an amoebo-flagellate found in most soil and freshwater habitats. The portal of entry is the nasopharynx from which the amoeba makes its way into the brain by penetration of the olfactory mucosa and cribriform plate. Diagnosis should be suspected in all cases of purulent meningitis and meningoencephalitis in which bacteria are not evident in the cerebrospinal fluid. Diagnosis can be made by microscopic examination of a fresh specimen of cerebrospinal fluid, or a specimen strained with Wright's or Gram's stain. Combination chemotherapy with amphotericin B and tetracycline, or amphotericin B and rifamycin, by intravenous, intrathecal, and when possible, intraventricular instillation, may offer some hope of success. Preventive measures include constant surveillance of domestic water supplies and swimming pools for amoebic contamination, and education of the public to avoid swimming in contaminated areas.

[Immunological Tests By Anti-Free-Living Amoebas Serum Produced In Experimental Animals: II. Indirect Fluorescent Antibody Titer Of Anti-free-living Amoebas Serum Produced In Rabbits]

The indirect fluorescent antibody test was performed to demonstrate the antibody production in the rabbits immunized with free-living amoebas; Acanthamoeba culbertsoni and Naegleria fowleri, and antibody titer changes by immunization duration. Rabbits were immunized with Acanthamoeba culbertsoni and Naegleria fowleri which were cultured axenically in CGVS medium. For experiments, rabbits were divided into two groups; small dose group received 10(4) intravenously with live or dead free-living amoebas trophozoites as an immunizing dose three times with one week interval, and large dose group received 10(6) live or dead trophozoites respectively. The control group received physiologic saline or medium for culture of free-living amoebas intravenously. Antiserum was collected 4 times at interval of 3 days in the first 10 days, and also up to 2 months later. In the group immunized with live Acanthamoeba culbertsoni, fluorescent antibody titer was higher than in the group of dead one, and also in the large dose group than in the small dose group. Antibody titer of anti-Naegleria fowleri serum in the large dose group showed no difference by the source of amoeba antigen; live or dead. But in the small dose group, antibody titer was higher in the immunized with live Naegleria fowleri than in the group with dead one. No cross reactivity was demonstrated between the Acanthamoeba and Naegleria. And no cross reaction was observed when the free-living amoebas antigens were tested against human sera of amoebiasis, paragonimiasis and clonorchiasis.

Isolation and identification of pathogenic Naegleria from Florida lakes

Five cases of primary amoebic meningoencephalitis associated with swimming in freshwater lakes have been recorded in Florida over the past 14 years. The present study demonstrated that pathogenic Naegleria, the causative agent, is relatively widespread. Twelve of 26 lakes sampled only once yielded the amoeba. Populations in three of five lakes sampled routinely reached levels of one amoeba per 25 ml of water tested during the hot summer months. Overwintering in freshwater lake bottom sediments was demonstrated, showing that thermal-discharge pollution of waters plays a miniscule, if any, role in the maintenance of pathogenic Naegleria in nature in this semitropical area.

Delayed type hypersensitivity in guinea pig infected subcutaneously with Naegleria fowleri Carter

A soluble fraction, derived from Naegleria fowleri trophozoites disrupted by freeze-thawing, was tested for antigenic properties. Intradermal injections of this preparation were administered to guinea pigs previously infected subcutaneously with viable N. fowleri. Delayed hypersensitivity to the antigen and loss of weight, the diagnostic symptom of visceral naegleriasis, were observed in the surviving animals. Fifty percent of the guinea pigs, however, did not lose weight and had a reduced reaction to the antigen. The apparent differences in the immunocompetence of guinea pigs inoculated subcutaneously and intranasally with N. fowleri are compared.

Comparative antigenic analysis of pathogenic and free-living Naegleria species by the gel diffusion and immunoelectrophoresis techniques

Antigens prepared from each of five strains (CA, CJ, HB-1, HB-3, and TY) of pathogenic Naegleria and the EG strain of nonpathogenic Naegleria gruberi were compared by the gel diffusion and immunoelectrophoresis techniques. Axenically grown amoebae were used as sources of antigens. Antisera were produced in individual rabbits against three strains (CA, CJ, and HB-1) of pathogenic Naegleria and the EG strain of N. gruberi. In the gel diffusion experiment each of the six antigens was reacted with each of the four antisera in agar gel. The results of these experiments revealed that the antigens of N. gruberi reacted strongly with the homologous antiserum but minimally with each of the three heterologous antisera. The antigens of all five pathogenic strains reacted extensively with the anti-CA, anti-CJ, and anti-HB-1 sera and moderately with the anti-EG serum. In the immunoelectrophoresis test each of the six antigens was separated electrophoretically in agar gel and reacted with each of the four antisera. The EG strain reacted extensively with its homologous antiserum and produced multiple precipitin arcs; it reacted minimally with anti-CA, anti-CJ, and anti-HB-1 sera and produced only three arcs. The antigens of all five strains of Naegleria fowleri reacted very strongly with anti-CA, anti-CJ, and anti-HB-1 sera and produced multiple precipitin arcs. They, however, reacted variably with the anti-EG serum and produced three to six precipitin arcs. Comparative immunoelectrophoretic analysis carried out on the CA and HB-1 strains revealed the antigenic identity of these two strains. Based on these results, together with those from the reciprocal absorption experiments, it was concluded that (i) the pathogenic strains of Naegleria, though they shared three to six common antigens with N. gruberi, were nevertheless distinct from it, and (ii) the five pathogenic strains were antigenically close and belonged in the same species. Antigens of Acanthamoeba castellanii, A. culbertsoni, and Entamoeba histolytica were also reacted with the four anti-Naegleria sera in gel diffusion experiments. Results of these tests indicate that these three organisms are antigenically distinct from Naegleria.

Infectious agent from a free-living soil amoeba, Naegleria gruberi

A subcellular infectious material has been found in a strain of the amoeba Naegleria gruberi, strain EG, which is capable of infecting chick embryo cells and causing them to undergo cytopathic changes with the release of more infectious material. The material is present in two lines of the amoeba which were separated shortly after the isolation of the strain and subsequently maintained in separate laboratories.

Primary amoebic meningoencephalitis in Britain

Meningoencephalitis proved to be due to an amoeba (Naegleria) has been diagnosed in Great Britain for the first time. The first patient (a boy of 2) survived longer than any previously recorded cases, but in spite of early diagnosis and treatment he died 15 days after the onset of meningeal symptoms.Two other children who were exposed to the same possible source of infection (a warm, muddy puddle) had similar symptoms and developed mild meningitis. A naegleria was isolated from the cerebrospinal fluid of one of them. Both recovered after treatment with amphotericin.

Primary amoebic meningoencephalitis in Britain

Primary amoebic meningoencephalitis is caused by amoebae of the genera Naegleria and Hartmannella (Acanthamoeba), which ordinarily are free-living saprophytes. The infection may be acquired from fresh water-for example, while bathing-the amoebae invading the nasal mucosa and reaching the meninges and brain along the olfactory nerve filaments. The disease is designated "primary" to distinguish it from meningocerebral infection caused by the parasitic amoebae, particularly Entamoeba histolytica, which invade the central nervous system only as a result of dissemination in the blood stream from lesions in other parts of the body.During histological reappraisal of old specimens in a medical museum in London an instance of amoebic meningoencephalitis histologically indistinguishable from the published cases has been found. The specimen dates from 1909. The patient was said to be from Essex. What may have been another case, seen in Northern Ireland in 1937, is also described briefly. These observations may indicate that this disease occurs in the British Isles.Primary amoebic meningoencephalitis should be considered in the differential diagnosis of every case of acute meningitis.

Amoebic meningoencephalitis: a new amoeba isolate

A strain of Naegleria sp. was isolated repeatedly from the spinal fluid of a boy who died of acute meningoencephalitis 5 days after the onset of the first symptoms.

Hyperbaric oxygen: toxicity to fish at pressures present in their swimbladders

When juvenile Pacific rock-fish, Sebastodes miniatus, are exposed to oxygen tensions equal to those in their swimbladders, they exhibit symptoms characteristic of oxygen poisoning in mammals and ultimately die. Thus their central nervous system appears to be as sensitive to elevated oxygen pressure as that of higher vertebrates, whereas the cells of the gas gland tissue inside the swimbladder must be insensitive to the partial pressure of oxygen which they help to produce.