Diagnosis of Encephalitozoon cuniculi infection by western blot and the use of cross-reactive antigens for the possible detection of microsporidiosis in humans

Therapeutic targets for the treatment of microsporidiosis in humans

INTRODUCTION

Microsporidia have been increasingly reported to infect humans. The most common presentation of microsporidiosis is chronic diarrhea, a significant mortality risk in immune-compromised patients. Albendazole, which inhibits tubulin, and fumagillin, which inhibits methionine aminopeptidase type 2 (MetAP2), are the two main therapeutic agents used for treatment of microsporidiosis. In addition, to their role as emerging pathogens in humans, microsporidia are important pathogens in insects, aquaculture, and veterinary medicine. New therapeutic targets and therapies have become a recent focus of attention for medicine, veterinary, and agricultural use. Areas covered: Herein, we discuss the detection and symptoms of microsporidiosis in humans and the therapeutic targets that have been utilized for the design of new drugs for the treatment of this infection, including triosephosphate isomerase, tubulin, MetAP2, topoisomerase IV, chitin synthases, and polyamines. Expert opinion: Enterocytozoon bieneusi is the most common microsporidia in human infection. Fumagillin has a broader anti-microsporidian activity than albendazole and is active against both Ent. bieneusi and Encephaliozoonidae. Microsporidia lack methionine aminopeptidase type 1 and are, therefore, dependent on MetAP2, while mammalian cells have both enzymes. Thus, MetAP2 is an essential enzyme in microsporidia and new inhibitors of this pathway have significant promise as therapeutic agents.

Production and characterization of monoclonal antibodies against Encephalitozoon intestinalis and Encephalitozoon sp. spores and their developmental stages

Background

Microsporidia are intracellular obligate parasites traditionally associated with immunosuppressed patients; their detection in immunocompetent patients has increased, highlighting their possible importance as emerging pathogens. Detection of spores in stools, urine, body fluids and tissues is difficult and immunological techniques such as immunofluorescence have proved to be a useful and reliable tool in the diagnosis of human microsporidiosis. For this reason, we have produced and characterized monoclonal antibodies (MAbs) specific for Encephalitozoon intestinalis (the second most frequent microsporidian infecting humans), and other Encephalitozoon species, that can be used in different diagnostic techniques.

Results

Seven MAbs were selected in accordance with their optical density (OD). Four (4C4, 2C2, 2E5 and 2H2) were isotype IgG2a; two (3A5 and 3C9) isotype IgG3, and one Mab, 1D7, IgM isotype. The selected monoclonal antibody-secreting hybridomas were characterized by indirect immunofluorescence antibody test (IFAT), enzyme-linked immunosorbent assay (ELISA), Western blot, immunoelectron microscopy (Immunogold) and in vitro cultures. The study by IFAT showed different behavior depending on the MAbs studied. The MAbs 4C4, 2C2, 2E5 and 2H2 showed reactivity against epitopes in the wall of the spore (exospore and endospore) epitopes located in Encephalitozoon sp. spores, whereas the MAbs 3A5, 1D7 and 3C9 showed reactivity against internal epitopes (cytoplasmic contents or sporoplasm) of E. intestinalis spores. All MAbs recognized the developing parasites in the in vitro cultures of E. intestinalis. Additionally, 59 formalin-fixed stool samples that had been previously analyzed were screened, with 26 (44%) presenting microsporidian spores (18 samples with E. intestinalis and 8 samples with Enterocytozoon bieneusi). Detection of microsporidian spores by microscopy was performed using Calcofluor stain, Modified Trichrome, Quick-Hot Gram Chromotrope, as well as IFAT using MAbs 4C4, 2C2, 2E5 and 2H2. The 4 MAbs tested clearly recognized the larger spores corresponding to E. intestinalis, but showed no reactivity with Enterocytozoon bieneusi spores. The mass spectrometry and proteomic study revealed that the Mabs 4C4, 2C2, 2E5 and 2H2 recognized the Spore Wall Protein 1 (SWP1) as the antigenic target.

Conclusions

The IFAT-positive MAbs exhibited excellent reactivity against spores and developmental stages, permitting their use in human and animal diagnosis. The epitopes recognized (exospore, endospore and cytoplasmic contents) by the different MAbs developed need further study, and may reveal potential targets for vaccine development, immunotherapy and chemotherapy.

Surveillance for an outbreak of Encephalitozoon cuniculi infection in rabbits housed at a zoo and biosecurity countermeasures

An outbreak of encephalitozoonosis occurred in a rabbit colony at a zoo in Japan. Throughout the two years after the onset, all 42 rabbits were investigated clinically, pathologically and serologically for prevention and control of the disease. Eleven rabbits (11/42, 26.2%) showed clinical symptoms. Of 38 rabbits examined to detect specific antibodies against Encephalitozoon cuniculi, 71.1% (n=27) were found seropositive; 20 out of 30 clinically healthy rabbits (except for 8 clinical cases) were seropositive. The infection rate was 76.2% (32/42), including 5 pathologically diagnosed cases. The results of serological survey revealed that asymptomatic infection was widespread, even among clinically healthy rabbits. However, encephalitozoonosis was not found by pathological examination in any other species of animals kept in the same area within the zoo. Isolation and elimination of the rabbits with suspected infection based on the results of serological examination were carried out immediately; however, encephalitozoonosis continued to occur sporadically. Therefore, all the remaining rabbits were finally slaughtered. Then, the facility was closed, and all the equipment was disinfected. After a two-month interval, founder rabbits were introduced from encephalitozoonosis-free rabbitries for new colony formation. Since then, encephalitozoonosis has not been seen in any animals at the zoo. In this study, biosecurity countermeasures including staff education, epidemiological surveillance and application of an "all-out and all-in" system for rabbit colony establishment based on serological examination were successfully accomplished with regard to animal hygiene and public health for the eradication of E. cuniculi.

Outbreak of microsporidiosis caused by Enterocytozoon bieneusi in falcons

Four falcons from a private collection of 137 falcons in Abu Dhabi (UAE) died suddenly in summer 2005. In order to screen for a possible disease among the remaining falcons in the aviary, all other birds were caught, examined and treated if necessary. Most of the falcons suffered from massive lice infestation and 74 falcons additionally from a heavy Caryospora sp. burden. Endoscopy revealed yellowish plaques on intestines, livers or kidneys in 70 birds (51.1% morbidity). Proliferative serositis was seen in 17 out of 24 necropsied birds with plaques on intestines, livers or kidneys, which did not resemble any known disease in falcons. However, apart from 20 falcons, which died within a 6-week period after the initial examinations due to advanced disease stages, all other falcons responded well to the treatment with dimetridazole (Emtryl), indicating protozoal disease. Immunohistochemistry confirmed the presence of microsporidial antigen. The final diagnosis of Enterocytozoon (E.) bieneusi genotype D was confirmed with materials from 6 birds by PCR and sequencing. To our knowledge this is the first report of microsporidiosis caused by E. bieneusi in raptors in general and in falcons in particular. However, it is still unclear for how long E. bieneusi was present in the falcon flock, and which role it played in the development of the disease. Predisposing factors such as high temperature and overcrowding in the aviary induced immune suppression causing massive lice infestation as well as coccidiosis, thus paving the way for invasion with microsporidial spores.

Carbohydrate moieties of microsporidian polar tube proteins are targeted by immunoglobulin G in immunocompetent individuals

Microsporidia of the Encephalitozoon species are frequently found as opportunistic pathogens of immunocompromised patients, but very little is known about the prevalence and significance of Encephalitozoon infection in immunocompetent individuals. It was reported previously that 8% of Dutch blood donors and 5% of pregnant French women had an immunoglobulin G (IgG) immune response against specific organelles of Encephalitozoon intestinalis. These organelles, the so-called polar tube and anchoring disk, are used to penetrate membranes of host cells during infection. The unexpectedly high percentage of immunocompetent individuals with IgG against these organelles suggested that infection of humans with microsporidia might be more common than previously recognized. In the present study, we analyzed this anti-Encephalitozoon IgG response by using indirect immunofluorescence, Western blotting, two-dimensional gel electrophoresis, and chemical deglycosylation. Our results show that the antibody response is directed against the posttranslational carbohydrate modification of the major polar tube protein (polar tube protein 1) and carbohydrate moieties of proteins in the anchoring region of the polar tube of Encephalitozoon. In addition, the antibodies were found to decrease the infectivity of E. intestinalis in vitro. The significance and possible origin of these prevalent antibodies are discussed.

Sensitivity and specificity of a monoclonal antibody-based fluorescence assay for detecting Enterocytozoon bieneusi spores in feces of simian immunodeficiency virus-infected macaques

Enterocytozoon bieneusi is clinically the most significant among the microsporidia causing chronic diarrhea, wasting, and cholangitis in individuals with human immunodeficiency virus/AIDS. Microscopy with either calcofluor or modified trichrome stains is the standard diagnostic test for microsporidiosis and does not allow species identification. Detection of E. bieneusi infection based on PCR is limited to a few reference laboratories, and thus it is not the standard diagnostic assay. We have recently reported the development and characterization of a panel of monoclonal antibodies against E. bieneusi, and in this publication we evaluated the specificity and sensitivity of an immunofluorescence assay (IFA), compared with PCR, in simian immunodeficiency virus-infected macaques. The IFA, which correlated with the primary PCR method, with a detection limit of 1.5 x 10(5) spores per gram of feces, will simplify considerably the detection of E. bieneusi spores in clinical and environmental specimens and in laboratory and epidemiological investigations.

Monoclonal antibodies for specific detection of Encephalitozoon cuniculi

Seven species-specific monoclonal antibodies (MAbs) were produced against Encephalitozoon cuniculi and characterized. The MAbs were immunoglobulin G, and when used for indirect microimmunofluorescence microscopy and Western immunoblot assays, they detected E. cuniculi originating from clinical samples. They did not cross-react with other Encephalitozoon species (E. intestinalis and E. hellem) or with a collection of gram-negative bacteria, yeast, and other parasites. The MAbs reacted primarily with 121-, 56-, 45-, 43-, and 41-kDa protein epitopes of E. cuniculi. These epitopes were demonstrated to be E. cuniculi species specific by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We developed MAbs to strains of E. cuniculi that can be used successfully to distinguish E. cuniculi from other microsporidial species in cultures established from clinical specimens. These MAbs may provide a specific, simple, rapid, and low-cost tool for the identification and diagnosis of infections due to microsporidia.

Purification of Enterocytozoon bieneusi from stools and production of specific antibodies

Enterocytozoon bieneusi is clinically the most significant of the microsporidia in humans, causing chronic diarrhea wasting and cholangitis in individuals with human immunodeficiency virus infection and AIDS. Little progress on this infection has been made because of the inability to propagate E. bieneusi in vitro and in vivo, which limits the source of parasite spores to the stools of infected human patients. Given the size and shape of the E. bieneusi spores (1.1 to 1.6 by 0.7 to 1.0 microm) and the lack of specific immune reagents, the identification and purification of large quantities of spores from feces are technically challenging. Consequently, diagnosis relies entirely on PCR, a labor-intensive approach that requires highly skilled personnel. We describe a method for the purification of E. bieneusi spores from human stools and the production of rabbit-specific antisera. Spores were purified by a combination of isopycnic Percoll gradient centrifugation and continuous sucrose gradient centrifugation. Specific polyclonal antibodies raised in mice and rabbits reacted by indirect immunofluorescence with E. bieneusi but not with Encephalitozoon spp., Candida albicans, Staphylococcus aureus, Escherichia coli, or other forms present in human stools.

Antigenic diversity of Encephalitozoon hellem demonstrated by subspecies-specific monoclonal antibodies

Encephalitozoon hellem is a unicellular, obligate intracellular microsporidian species detected and isolated in HIV-infected patients presenting with keratoconjunctivitis, sinusitis, tracheobronchitis, nephritis, cystitis, and disseminated infection. A total of 24 monoclonal antibodies were produced against E. hellem and characterized. The monoclonal antibodies were of the immunoglobulin (Ig) G and Ig M subclasses, and, when incorporated into indirect immunofluorescence and immunoblotting assays, reacted against 13 isolates of E. hellem originating from three geographic regions. These monoclonal antibodies did not react with one strain each of either Encephalitozoon intestinalis or Encephalitozoon cuniculi, demonstrating their specificity. Two monoclonal antibodies reacted with all karyotype B-E. hellem isolates but did not react with karyotype A-isolates from North America and the Netherlands, thus demonstrating antigenic diversity among E. hellem isolates. These results add to the increasing evidence for diversity among E. hellem, which therefore may be reclassified into subspecies.

An indirect ELISA for detection of Encephalitozoon cuniculi infection in farmed blue foxes (Alopex lagopus)

Infection with the intracellular microsporidium Encephalitozoon cuniculi can cause serious disease, encephalitozoonosis, in the blue fox (Alopex lagopus). The disease diagnosis is based on clinical signs and pathological findings, and detection of E. cuniculi or circulating antibodies directed against the parasite. Indirect immunofluorescence (IFAT) and carbon immunoassay (CIA) are the most commonly used serological methods for diagnosis in this species. In the present study, an indirect ELISA (enzyme linked immunosorbent assay) was established and evaluated against IFAT by testing of 205 field samples from blue foxes. There was high agreement between the results of the ELISA and CIA (kappa=0.99), and the ELISA and IFAT (kappa=0.958). There was no significant statistical difference between the tests (p>0.05). It was concluded that the ELISA could be used to identify seropositive farmed blue foxes. The advantage of the ELISA lies in the potential of screening large numbers of animals with the goal of eradicating E. cuniculi infection in the farms.

Microsporidia: emerging pathogenic protists

Microsporidia are eukaryotic spore forming obligate intracellular protozoan parasites first recognized over 100 years ago. These organisms infect all of the major animal groups and are now recognized as opportunistic pathogens of humans. Microsporidian spores are common in the environment and microsporidia pathogenic to humans have been found in water supplies. The genera Nosema, Vittaforma, Brachiola, Pleistophora, Encephalitozoon, Enterocytozoon, Septata (reclassified to Encephalitozoon) and Trachipleistophora have been found in human infections. These organisms have the smallest known eukaryotic genomes. Microsporidian ribosomal RNA sequences have proven useful as diagnostic tools as well as for phylogenetic analysis. Recent phylogenetic analysis suggests that Microsporidia are related to the fungi. These organisms are defined by the presence of a unique invasion organelle consisting of a single polar tube that coils around the interior of the spore. All microsporidia exhibit the same response to stimuli, that is, the polar tube discharges from the anterior pole of the spore in an explosive reaction. If the polar tube is discharged next to a cell, it can pierce the cell and transfer its sporoplasm into the cell. A technique was developed for the purification of polar tube proteins (PTPs) using differential extraction followed by reverse phase HPLC. This method was used to purify the PTPs from Glugea americanus, Encephalitozoon cuniculi, Enc. hellem and Enc. intestinalis. These PTPs demonstrate conserved characteristics such as solubility, hydrophobicity, mass, proline content and immunologic epitopes. The major PTP gene from Enc. cuniculi and Enc. hellem has been cloned and expressed in vitro. The gene sequences support the importance of ER and in the formation of the polar tube as suggested by morphologic studies. Analysis of the cloned proteins also indicates that secondary structural characteristics are conserved. These characteristics are probably important in the function of this protein during the eversion/assembly of the polar tube and in providing elasticity and resiliency for sporoplasm passage.

Discrimination between viable and dead Encephalitozoon cuniculi (Microsporidian) spores by dual staining with sytox green and calcofluor white M2R

Microsporidia are obligate intracellular parasites, recognized as causing chronic diarrhea and systemic disease in AIDS patients, organ transplant recipients, travelers, and malnourished children. Species of microsporidia that infect humans have been detected in drinking-water sources, and methods are needed to ascertain if these microsporidia are viable and capable of causing infections. In this study, Calcofluor White M2R and Sytox Green stains were used in combination to differentiate between live (freshly harvested) and dead (boiled) Encephalitozoon cuniculi spores. Calcofluor White M2R binds to chitin in the microsporidian spore wall. Dual-stained live spores appeared as turquoise-blue ovals, while dead spores appeared as white-yellow ovals at an excitation wavelength of 395 to 415 nm used for viewing the Calcofluor stain. Sytox Green, a nuclear stain, is excluded by live spores but penetrates compromised spore membranes. Dual-stained dead spores fluoresced bright yellow-green when viewed at an excitation wavelength of 470 to 490 nm, whereas live spores failed to stain with Sytox Green. After live and dead spores were mixed at various ratios, the number of viably stained spores detected in the dual-staining procedure correlated (P = 0.0025) with the expected numbers of viable spores. Spore mixtures were also assayed for infectivity in a focus-forming assay, and a correlation (P = 0.0002) was measured between the percentage of focus-forming microsporidia and the percentage of expected infectious spores in each mixture. By analysis of variance, no statistically significant differences were measured between the percentage of viably stained microsporidia and the percentage of infectious microsporidia (P = 0.964) in each mixture. These results suggest that Calcofluor White M2R and Sytox Green stains, when used together, may facilitate studies to identify viable microsporidia.

Production of monoclonal antibodies directed against the microsporidium Enterocytozoon bieneusi

Several hybridomas producing antibodies detected by indirect immunofluorescence antibody test (IFAT) were established by fusion of mouse myeloma SP2/O with spleen cells from BALB/c mice immunized against whole spores (protocol 1) or chitinase-treated spores (protocol 2) of Enterocytozoon bieneusi and were cloned twice by limiting dilutions. Two monoclonal antibodies (MAbs), 3B82H2 from protocol 1, isotyped as immunoglobulin M (IgM), and 6E52D9 from protocol 2, isotyped as IgG, were expanded in both ascites and culture. IFAT with the MAbs showed that both MAbs reacted exclusively with the walls of the spores of E. bieneusi, strongly staining the surface of mature spores, and produced titers of greater than 4,096. Immunogold electron microscopy confirmed the specific reactivities of both antibodies. No cross-reaction, either with the spores of the other intestinal microsporidium species Encephalitozoon intestinalis or with yeast cells, bacteria, or any other intestinal parasites, was observed. The MAbs were used to identify E. bieneusi spores in fecal specimens from patients suspected of having intestinal microsporidiosis. The IFAT was validated against standard staining methods (Chromotrope 2R and Uvitex 2B) and PCR. We report here the first description and characterization of two MAbs specific for the spore wall of E. bieneusi. These MAbs have great potential for the demonstration and species determination of E. bieneusi, and their application in immunofluorescence identification of E. bieneusi in stool samples could offer a new diagnostic tool for clinical laboratories.

Detection by an immunofluorescence test of Encephalitozoon intestinalis spores in routinely formalin-fixed stool samples stored at room temperature

Of the several microsporidia that infect humans, Enterocytozoon bieneusi is known to cause a gastrointestinal disease whereas Encephalitozoon intestinalis causes both a disseminated and an intestinal disease. Although several different staining techniques, including the chromotrope technique and its modifications, Uvitex 2B, and the quick-hot Gram-chromotrope procedure, detect microsporidian spores in fecal smears and other clinical samples, they do not identify the species of microsporidia. A need for an easily performed test therefore exists. We reevaluated 120 stool samples that had been found positive for microsporidia previously, using the quick-hot Gram-chromotrope technique, and segregated them into two groups on the basis of spore size. We also screened the smears by immunofluorescence microscopy, using a polyclonal rabbit anti-E. intestinalis serum at a dilution of 1:400. Spores in 29 (24.1%) of the 120 samples fluoresced brightly, indicating that they were E. intestinalis spores. No intense background or cross-reactivity with bacteria, yeasts, or other structures in the stool samples was seen. Additionally, the numbers of spores that fluoresced in seven of these samples were substantially smaller than the numbers of spores that were present in the stained smears, indicating that these samples were probably derived from patients with mixed infections of Enterocytozoon bieneusi and E. intestinalis. Because a 1:400 dilution of this serum does not react with culture-grown Encephalitozoon hellem, Encephalitozoon cuniculi, or Vittaforma corneae or with Enterocytozoon bieneusi spores in feces, we concluded that an immunofluorescence test using this serum is a good alternative for the specific identification of E. intestinalis infections.

Molecular techniques for detection, species differentiation, and phylogenetic analysis of microsporidia

Microsporidia are obligate intracellular protozoan parasites that infect a broad range of vertebrates and invertebrates. These parasites are now recognized as one of the most common pathogens in human immunodeficiency virus-infected patients. For most patients with infectious diseases, microbiological isolation and identification techniques offer the most rapid and specific determination of the etiologic agent. This is not a suitable procedure for microsporidia, which are obligate intracellular parasites requiring cell culture systems for growth. Therefore, the diagnosis of microsporidiosis currently depends on morphological demonstration of the organisms themselves. Although the diagnosis of microsporidiosis and identification of microsporidia by light microscopy have greatly improved during the last few years, species differentiation by these techniques is usually impossible and transmission electron microscopy may be necessary. Immunfluorescent-staining techniques have been developed for species differentiation of microsporidia, but the antibodies used in these procedures are available only at research laboratories at present. During the last 10 years, the detection of infectious disease agents has begun to include the use of nucleic acid-based technologies. Diagnosis of infection caused by parasitic organisms is the last field of clinical microbiology to incorporate these techniques and molecular techniques (e.g., PCR and hybridization assays) have recently been developed for the detection, species differentiation, and phylogenetic analysis of microsporidia. In this paper we review human microsporidial infections and describe and discuss these newly developed molecular techniques.

Polar tube proteins of microsporidia of the family encephalitozoonidae

Encephalitozoonidae are microsporidia associated with human infections including hepatitis, encephalitis, conjunctivitis, and disseminated disease. Microsporidia produce a small resistant spore containing a polar tube which serves as a unique vehicle of infection. Polar tube proteins (PTPs) from Encephalitozoon hellem. Encephalitozoon (Septata) intestinalis, and Encephalitozoon cuniculi were purified to homogeneity by HPLC. By SDS-PAGE, the Mr of E. hellem PTP was 55 kDa, while the Mr of E. intestinalis and E. cuniculi PTP was 45 kDa. Polyclonal rabbit antiserum to these purified PTPs localized to polar filaments by immunogold electron microscopy and immunofluorescence, and demonstrated cross-reactivity by both immunoblotting and immunogold electron microscopy. These PTPs have similar solubility properties, hydrophobicity, and proline content to a 43-kDa PTP we have previously purified from Glugea americanus, a fish microsporidium. As the polar tube is critical in the transmission of this organism, further study of PTPs may lead to the development of new therapeutic strategies and diagnostic tests.

The molecular characterization of the major polar tube protein gene from Encephalitozoon hellem, a microsporidian parasite of humans

The microsporidia are obligate intracellular protozoan parasites of increasing importance as human pathogens, which are characterized by a small resistant spore with a single polar filament that coils around the sporoplasm. When stimulated, the polar filament rapidly everts out of the spore to form a hollow polar tube through which the sporoplasm passes, thus serving as a unique mechanism of transmission. A genomic library of the human microsporidium Encephalitozoon hellem was screened using a polyclonal rabbit antibody (anti-PTP Eh55) produced to the major HPLC purified polar tube protein (PTP) of E. hellem. This antibody localized to intrasporal polar filaments and extrasporal polar tubes of E. hellem by immunogold electron microscopy confirming the polar tube specificity of the antibody. A total of 14 anti-PTP Eh55 reactive genomic clones were identified and purified. A PTP gene was identified consisting of 1362 bp coding for 453 amino acids. The N-terminus of the translated protein consists of aputative N-terminal signal sequence of 22 amino acids, which when cleaved results in a mature protein of 431 amino acids with a predicted molecular mass of 43 kDa. The protein has a high proline content (14.6%) and contains a central domain of six alternating tandem repeats of 20 amino acids. After ligation of the gene into a glutathione S-transferase (GST) expression vector, a fusion protein was produced that reacted by immunoblotting with the polar tube specific anti-PTP Eh55. The gene was present as a single copy in the genome and there was no homology with other known genes. As the polar tube is a critical structure for the transmission of this organism to a new host cell, further study of PTPs may lead to the development of new therapeutic strategies and diagnostic tests.

Natural pathogens of laboratory mice, rats, and rabbits and their effects on research

Laboratory mice, rats, and rabbits may harbor a variety of viral, bacterial, parasitic, and fungal agents. Frequently, these organisms cause no overt signs of disease. However, many of the natural pathogens of these laboratory animals may alter host physiology, rendering the host unsuitable for many experimental uses. While the number and prevalence of these pathogens have declined considerably, many still turn up in laboratory animals and represent unwanted variables in research. Investigators using mice, rats, and rabbits in biomedical experimentation should be aware of the profound effects that many of these agents can have on research.

Immunocytochemical identification of spore proteins in two microsporidia, with emphasis on extrusion apparatus

Microsporidia can form small spores with a unique invasive apparatus featuring a long polar tube whose extrusion allows entry of infectious sporoplasm into a host cell. The reactivity of mouse polyclonal antibodies raised against sporal proteins from two microsporidian species belonging to different genera (Glugea atherinae and Encephalitozoon cuniculi) was studied by western blotting and indirect immunofluorescence. Whole protein antisera provided a few cross-reactions relatable to some proteins of the spore envelope or polar tube. Ultrastructural immunocytochemistry with murine antibodies against protein bands separated by sodium dodecylsulphate polyacrylamide gel electrophoresis allowed the assignment of several proteins to the polar tube (34, 75 and 170 kDa in Glugea, 35, 55 and 150 kDa in Encephalitozoon). Antigenic similarities were detected for the Glugea 34 kDa and Encephalitozoon 35 kDa polar tube proteins. Species-specific proteins were shown to be located in either the lamellar polaroplast of Glugea or the spore envelope of Encephalitozoon.

Identification of Encephalitozoon intestinalis in travelers with chronic diarrhea by specific PCR amplification

With the use of Weber's modified trichrome and Uvitex 2B techniques, spores of microsporidia were detected in the stools of four travelers presenting clinically with chronic diarrhea. The general health of these patients was not impaired, and human immunodeficiency virus screening was negative. Immune evaluation, including the study of lymphocytic subpopulations, assay of serum immunoglobulins, and an intradermal multitest, showed normal results. Molecular identification of microsporidian species was based on the PCR amplification of a small-subunit rRNA sequence followed by HinfI endonuclease restriction. Encephalitozoon intestinalis microsporidiosis was thus shown in two of the four patients examined. In two patients, therapy based on albendazole made stools devoid of microsporidian spores without influence on the intestinal disorders. The pathogenic role of E. intestinalis in immunocompetent individuals remains to be demonstrated.

Simple diagnosis of Encephalitozoon sp. microsporidial infections by using a panspecific antiexospore monoclonal antibody

Microsporidia (phylum Microsproa) have recently become recognized as common opportunistic protozoans in the United States and worldwide, particularly affecting immunodeficient patients. Microsporidian organisms within the genus Encephalitozoon are the cause of nephrologic, ophthalmic, pneumologic, gastroenteric, and systemic infections. However, diagnosis of the small spores by light microscopy is difficult, even with newly developed and improved staining techniques. We have developed an anti-Encephalitozoon species monoclonal antibody-based immunoassay for easy diagnosis. A hybridoma was produced and selected following one main criterion: recognition by immunofluorescence of all known Encephalitozoon spores affecting humans. The selected monoclonal antibody-secreting hybridomas were characterized by enzyme-linked immunosorbent assay, immunofluorescence, Western blot, and immunoelectron microscopy using Encephalitozoon species from fresh and fixed samples from patients and from in vitro cultures. In the immunofluorescence assay, one monoclonal antibody, termed 3B6, strongly recognized Encephalitozoon cuniculi, E. hellem, and E. intestinalis. Monoclonal antibody 3B6 bound to other microsporidia (Nosema and Vairimorpha spp.) without cross-reacting with any other parasite, including Enterocytozoon bieneusi, fungus, or bacterium tested. In immunoelectron microscopy assays, monoclonal antibody 3B6 bound to the exospore of Encephalitozoon species, while in Western blot assays, it recognized three to seven antigens with molecular masses ranging from 34 to 117 kDa. We have developed a sensitive and specific monoclonal antibody-based immunoassay to diagnose common microsporidian infections, particularly with Encephalitozoon species. This is a new tool for identifying spores in bodily fluids and biopsy samples and is an efficient diagnostic test. Additionally, monoclonal antibody 3B6 can serve to assess the prevalence of microsporidial infections in immunodeficient and immunocompetent patients.

Waterborne protozoan pathogens

Protozoan parasites were the most frequently identified etiologic agents in waterborne disease outbreak from 1991 to 1994. The waterborne parasites Giardia lamblia, Naegleria fowleri, Acanthamoeba spp., Entamoeba histolytica, Cryptosporidium parvum, Cyclospora cayetanesis, Isospora belli, and the microsporidia are reviewed. For each parasite, the review includes history, life cycle, incidence, symptoms, and therapy. Clinical detection methods are compared, and emerging technologies are discussed. Information on the association of these parasites with waterborne outbreaks is reviewed. Current information on protozoan parasites identified as etiological agents in waterborne outbreaks is discussed. Water industry issues related to recent disease outbreaks are examined in the context of water quality testing regulations for G. lamblia and those proposed for C. parvum. The review identifies the limitations of the American Society of Testing and Materials water-testing method for these parasites. An overview of federal regulations affecting the water industry and laboratories that test for water quality is also provided. The article highlights the importance of the clinical laboratory as a frontline defense for the detection of infectious organisms. The review points to the need for clinical laboratories, physicians, and public health personnel to cooperatively plan and assess the challenge of meeting this potential public health threat.

Diagnosis of disseminated microsporidian Encephalitozoon hellem infection by PCR-Southern analysis and successful treatment with albendazole and fumagillin

A 37-year old AIDS patient presented with foreign body sensation. Microsporidia were detected in smears from a conjunctival swab and urine sediment stained with calcofluor and a modified trichrome blue stain and by indirect fluorescent-antibody staining with murine polyclonal antiserum raised against Encephalitozoon hellem. This antiserum cross-reacted with other Encephalitozoon species, so PCR was performed to amplify the microsporidian ribosomal DNA (rDNA) with pan-Encephalitozoon primers. The PCR DNA products from the urine and conjunctival clinical specimens, along with the tissue culture-derived microsporidian controls, were assayed by Southern analysis with oligonucleotide probes specific for Encephalitozoon cuniculi, E. hellem, and Encephalitozoon (Septata) intestinalis. The PCR product amplified from the urine specimen hybridized with the E. hellem probe only, while insufficient DNA was amplified from the conjunctiva specimen for detection by Southern analysis. For corroboration of the PCR-Southern analysis results, aliquots of the urine and conjunctiva specimens were seeded onto RK-13 cell monolayers. The rDNA extracts of the cultured microsporidia were amplified by PCR with pan-Encephalitozoon primers, and the PCR DNA products were subjected to digestion with restriction endonuclease FokI. The amplified rDNA of both the urine and conjunctiva isolates generated digestion patterns that were identified to the E. hellem PCR rDNA digestion pattern. In addition, double-stranded heteroduplex mobility shift analysis with these PCR products indicated that the urine and conjunctiva isolates were identical to each other and to E. hellem. The patient was treated with albendazole and topical fumagillin and responded rapidly, with no recurrence of ophthalmologic signs. The results of this study demonstrate that PCR-Southern analysis provides a basis for distinguishing E. cuniculi, E. hellem, and E. intestinalis in clinical specimens.

Encephalocytozoon intestinalis-specific monoclonal antibodies for laboratory diagnosis of microsporidiosis

Two monoclonal antibodies which can be used for the unambiguous identification by fluorescence microscopy of Encephalitozoon intestinalis spores in clinical specimens are described. Monoclonal antibody Si91 is specific for the extruded polar filament, and Si13 recognizes the surfaces of E. intestinalis spores. No cross-reaction with spores of Encephalitozoon hellem was observed. Immunogold electron microscopy confirmed the specific reactivities of both antibodies. Combined in an indirect immunofluorescence assay, these antibodies are used to identify spores in feces. Although there was some cross-reaction with fecal bacteria and fungi, the typical morphology of the extruded polar filaments enabled proper identification of the E. intestinalis spores. Parasites could also be demonstrated to be present in urine, nasal swabs, lung brush biopsy specimens, and bronchoalveolar lavage fluid from a patient with disseminated infection with E. intestinalis. The use of these monoclonal antibodies facilitates the detection and species determination of E. intestinalis in clinical specimens.

Identification of a microsporidian polar tube protein reactive monoclonal antibody

The microsporidia are characterized by spores containing a single polar tube that coils around the sporoplasm. When triggered by appropriate stimuli, the polar tube rapidly discharges out of the spore forming a hollow tube. The sporoplasm passes out of the spore through this tube serving as a unique vehicle of infection. Due to the unusual functional and solubility properties of the polar tube, the proteins comprising it are likely to be members of a protein family with a highly conserved amino acid composition among the various microsporidia. Polar tube proteins were separated from the majority of other proteins in glass bead disrupted spores of Glugea americanus using sequential 1% sodium dodecyl sulfate (SDS) and 9M urea extractions. The resultant spore pellet demonstrated broken, empty spore coats and numerous polar tubes in straight and twisted formations by negative stain transmission electron microscopy. After subsequent incubation of the pellet with 2% dithiothreitol (DTT), empty spore coats were still observed but the polar tubes were no longer present in the pellet. The DTT supernatant demonstrated four major protein bands by SDS-PAGE: 23, 27, 34 and 43 kDa. Monoclonal antibodies were produced to these proteins using Hunter's Titermax adjuvant. Mab 3C8.23.1 which cross-reacted with a 43-kDa antigen by immunoblot analysis, demonstrated strong reactivity with the polar tube of G. americanus spores by immunogold electron microscopy. This antibody will be useful in further characterization of polar tube proteins and may lead to novel diagnostic and therapeutic reagents.

Comparison of three staining methods for detecting microsporidia in fluids

Calcofluor white 2MR, modified trichrome blue, and indirect immunofluorescent antibody (IFA) staining methods were evaluated and compared for detecting microsporidia in stool. Serial 10-fold dilutions of Encephalitozoon (Septata) intestinalis were prepared in three formalinized stool specimens or in Tris-buffered saline. Ten-microliter aliquots were smeared onto glass slides, fixed with methanol, stained, and read by at least three individuals. The results indicated that the calcofluor stain was the most sensitive method, required approximately 15 min to perform, but did generate some false-positive results due to similarly staining small yeast cells. The modified trichrome blue stain was nearly as sensitive as the calcofluor stain and allowed for easier distinction between microsporidia and yeast cells. This stain, however, required approximately 60 min to perform. The IFA stain with polyclonal murine antiserum against E. intestinalis was the least sensitive of the methods and required approximately 130 min to perform. The lower limit of detection with the calcofluor and modified trichrome stains was a concentration of about 500 organisms in 10 microliters of stool to detect one microsporidian after viewing 50 fields at a final magnification of x1,000. Reliability was also addressed by use of 74 stool, urine, and intestinal fluid specimens, 50 of which were confirmed for the presence of microsporidia by transmission electron microscopy (TEM). All TEM-positive specimens were detected by calcofluor and modified trichrome blue staining. Ten specimens were not detected by the IFA stain. An additional seven TEM-negative specimens were read positive for microsporidia with the calcofluor stain, and of these, five also were read positive with the modified trichrome blue stain. The resulting diagnostic paradigm was to screen specimens with the calcofluor stain and to confirm the results with the modified trichrome stain. IFA, which was less sensitive, may become useful for microsporidian species identification as specific antibodies become available.

Parasitic infections of the central nervous system in children. Part II: Disseminated infections

In the second segment of this three-part review of parasitic infections of the central nervous system in children, we consider parasitic infections which typically involve various tissues and organs in addition to the brain and spinal cord. Parasites capable of dissemination in immunocompetent hosts are discussed first, and, as in Part I, organisms are grouped according to their predominant geographic location. This is followed by a discussion of the unique aspects of toxoplasmosis, strongyloidiasis and infection with microsporidia in immunocompromised patients, with an emphasis on the central nervous system.

Polyclonal and monoclonal antibody and PCR-amplified small-subunit rRNA identification of a microsporidian, Encephalitozoon hellem, isolated from an AIDS patient with disseminated infection

Microsporidia are primitive, spore-forming, mitochondria-lacking, eukaryotic protozoa that are obligate intracellular parasites. They are known to parasitize almost every group of animals including humans. Recently, microsporidia have increasingly been found to infect patients with AIDS. Five genera (Encephalitozoon, Enterocytozoon, Nosema, Septata, and Pleistophora) of microsporidia are known to infect humans. Enterocytozoon organisms cause gastrointestinal disease in a majority of AIDS patients with microsporidiosis. However, a smaller, but an expanding, number of patients with AIDS are being diagnosed with ocular and disseminated infection with Encephalitozoon hellem. Although microsporidial spores can be identified in clinical samples by a staining technique such as one with Weber's chromotrope stain, identification to the species level is dependent on cumbersome and time-consuming electron microscopy. We have recently isolated and established in continuous culture several strains of E. hellem from urine, bronchoalveolar lavage, and sputum samples from AIDS patients with disseminated microsporidiosis. We developed polyclonal and monoclonal antibodies and PCR primers to a strain of E. hellem that can be used successfully to identify E. hellem from other species of microsporidia either in clinical specimens or in cultures established from clinical specimens. Since patients infected with Encephalitozoon spp. are known to respond favorably to albendazole, identification of the parasite to the species level would be invaluable in the treatment of disseminated microsporidiosis.

Human microsporidial infections

Microsporidia are obligate intracellular spore-forming protozoal parasites belonging to the phylum Microspora. Their host range is extensive, including most invertebrates and all classes of vertebrates. More than 100 microsporidial genera and almost 1,000 species have now been identified. Five genera (Enterocytozoon spp., Encephalitozoon spp., Septata spp., Pleistophora sp., and Nosema spp.) and unclassified microsporidia (referred to by the collective term Microsporidium) have been associated with human disease, which appears to manifest primarily in immunocompromised persons. The clinical manifestations of microsporidiosis are diverse and include intestinal, pulmonary, ocular, muscular, and renal disease. Among persons not infected with human immunodeficiency virus, ten cases of microsporidiosis have been documented. In human immunodeficiency virus-infected patients, on the other hand, over 400 cases of microsporidiosis have been identified, the majority attributed to Enterocytozoon bieneusi, an important cause of chronic diarrhea and wasting. Diagnosis of microsporidiosis currently depends on morphological demonstration of the organisms themselves. Initial detection of microsporidia by light microscopic examination of tissue sections and of more readily obtainable specimens such as stool, duodenal aspirates, urine, sputum, nasal discharge, bronchoalveolar lavage fluid, and conjunctival smears is now becoming routine practice. Definitive species identification is made by using the specific fluorescein-tagged antibody (immunofluorescence) technique or electron microscopy. Treatment options are limited, but symptomatic improvement of Enterocytozoon bieneusi infection may be achieved with the anthelmintic-antiprotozoal drug albendazole. Preliminary observations suggest that Septata intestinalis and Encephalitozoon infections may be cured with albendazole. Progress is being made with respect to in vitro propagation of microsporidia, which is crucial for developing antimicrosporidial drugs. Furthermore, molecular techniques are being developed for diagnostic purposes, taxonomic classification, and analysis of phylogenetic relationships of microsporidia.

Detection of microsporidia by indirect immunofluorescence antibody test using polyclonal and monoclonal antibodies

During a screening for monoclonal antibodies (MAbs) to the microsporidian Encephalitozoon hellem, three murine hybridoma cell lines producing strong enzyme-linked immunosorbent assay (ELISA) reactivities were cloned twice, were designated C12, E9, and E11, and were found to secrete MAbs to the immunoglobulin M isotype. On subsequent ELISAs, the three MAbs reacted most strongly to E. hellem, and they reacted somewhat less to Encephalitozoon cuniculi and least to Nosema corneum, two other microsporidian species. The MAbs produced values of absorbance against microsporidia that were at least three times greater than reactivities obtained with control hybridoma supernatants or with uninfected host cell proteins used as antigens. By Western blot immunodetection, the three MAbs detected three E. hellem antigens with relative molecular weights (M(r)s) of 62, 60, and 52 when assayed at the highest supernatant dilutions producing reactivity. At lower dilutions, the MAbs detected additional proteins with M(r)s of 55 and 53. By using indirect immunofluorescence antibody staining, the MAbs, as well as hyperimmune polyclonal murine antisera raised against E. cuniculi and E. hellem, were able to detect formalin-fixed, tissue culture-derived E. cuniculi and E. hellem and two other human microsporidia, Enterocytozoon bieneusi and Septata intestinalis, in formalin-fixed stool and urine, respectively. E. bieneusi, however, stained more intensely with the polyclonal antisera than with the MAbs. Neither the MAbs nor the hyperimmune murine polyclonal antibodies detected Cryptosporidium, Giardia, Trichomonas, or Isospora spp. At higher concentrations, the polyclonal antisera did stain N. corneum and yeast cells. The background staining could be absorbed with Candida albicans. These results demonstrate that polyclonal antisera to E. cuniculi and E. hellem, as well as MAbs raised against E. hellem, can be used for indirect immunofluorescence antibody staining to detect several species of microsporidia known to cause opportunistic infections in AIDS patients.