Pathology of symptomatic microsporidial (Encephalitozoon hellem) bronchiolitis in the acquired immunodeficiency syndrome: a new respiratory pathogen diagnosed from lung biopsy, bronchoalveolar lavage, sputum, and tissue culture

Encephalitozoon spp. as a potential human pathogen

Encephalitzoon spp. are microsporidia, and intracellular opportunistic pathogens. The hosts of these pathogens include vertebrates, invertebrates, and certain protozoa. In people microsporidia may be opportunistic pathogens for immunocompromised patients (with AIDS or after organ transplantation). Infection with these microorganisms was also described in persons with diarrhea and corneal diseases.

The species causing rare infections in humans, Encephalitozooncuniculi, had previously been described from animal hosts. However, several new microsporidial species, including E. intestinalis and E. hellem, have been discovered in humans, raising the question of their natural origin. Vertebrate animals are now identified as hosts for all three microsporidial species infecting humans, implying a zoonotic nature of these microorganisms. Molecular studies have identified phenotypic and/or genetic variability within these species, indicating that they are not uniform, and have allowed the question of their zoonotic potential to be addressed. The focus of this review is to present the zoonotic potential of E. intestinalis, E. cuniculi, and E. hellem.

A new microsporidian parasite, Ordospora pajunii sp. nov (Ordosporidae), of Daphnia longispina highlights the value of genomic data for delineating species boundaries

Speciation is a complex and continuous process that makes the delineation of species boundaries a challenging task in particular in species with little morphological differentiation, such as parasites. In this case, the use of genomic data is often necessary, such as for the intracellular Microsporidian parasites. Here we characterize the genome of a gut parasite of the cladoceran Daphnia longispina (isolate FI-F-10), which we propose as a new species within the genus Ordospora: O. pajunii sp. nov (Ordosporidae). FI-F-10 closest relative, O. colligata is only found in D. magna. Both microsporidian species share several morphological features. Although it is not possible to estimate divergence times for Microsporidia due to the lack of fossil records and accelerated evolutionary rates, we base our proposal on the phylogenomic and genomic distances between both microsporidian lineages. Phylogenomic reconstruction shows that FI-F-10 forms an early diverging branch basal to the cluster that contains all known O. colligata strains. Whole-genome comparisons show that FI-F-10 presents a greater divergence at the sequence level than observed among O. colligata strains, and its genomic Average Nucleotide Identity (ANI) values against O. colligata are beyond the intra-specific range previously established for yeast and prokaryotes. Our data confirm that the ANI metrics are useful for fine genetic divergence calibration across Microsporidia taxa. In combination with phylogenetic and ecological data, genome-based metrics provide a powerful approach to delimitate species boundaries.

Chronic Infections in Mammals Due to Microsporidia

Microsporidia are pathogenic organism related to fungi. They cause infections in a wide variety of mammals as well as in avian, amphibian, and reptilian hosts. Many microsporidia species play an important role in the development of serious diseases that have significant implications in human and veterinary medicine. While microsporidia were originally considered to be opportunistic pathogens in humans, it is now understood that infections also occur in immune competent humans. Encephalitozoon cuniculi, Encephalitozoon intestinalis, and Enterocytozoon bieneusi are primarily mammalian pathogens. However, many other species of microsporidia that have some other primary host that is not a mammal have been reported to cause sporadic mammalian infections. Experimental models and observations in natural infections have demonstrated that microsporidia can cause a latent infection in mammalian hosts. This chapter reviews the published studies on mammalian microsporidiosis and the data on chronic infections due to these enigmatic pathogens.

Microsporidiosis in Humans

Microsporidia are obligate intracellular pathogens identified ∼150 years ago as the cause of pébrine, an economically important infection in silkworms. There are about 220 genera and 1,700 species of microsporidia, which are classified based on their ultrastructural features, developmental cycle, host-parasite relationship, and molecular analysis. Phylogenetic analysis suggests that microsporidia are related to the fungi, being grouped with the Cryptomycota as a basal branch or sister group to the fungi. Microsporidia can be transmitted by food and water and are likely zoonotic, as they parasitize a wide range of invertebrate and vertebrate hosts. Infection in humans occurs in both immunocompetent and immunodeficient hosts, e.g., in patients with organ transplantation, patients with advanced human immunodeficiency virus (HIV) infection, and patients receiving immune modulatory therapy such as anti-tumor necrosis factor alpha antibody. Clusters of infections due to latent infection in transplanted organs have also been demonstrated. Gastrointestinal infection is the most common manifestation; however, microsporidia can infect virtually any organ system, and infection has resulted in keratitis, myositis, cholecystitis, sinusitis, and encephalitis. Both albendazole and fumagillin have efficacy for the treatment of various species of microsporidia; however, albendazole has limited efficacy for the treatment of Enterocytozoon bieneusi. In addition, immune restoration can lead to resolution of infection. While the prevalence rate of microsporidiosis in patients with AIDS has fallen in the United States, due to the widespread use of combination antiretroviral therapy (cART), infection continues to occur throughout the world and is still seen in the United States in the setting of cART if a low CD4 count persists.

Lung Infections

A review of pulmonary infections of all types with diagnostic and morphological features.

Fatal Pulmonary Microsporidiosis Due toEncephalitozoon cuniculiFollowing Allogeneic Bone Marrow Transplantation for Acute Myelogenous Leukemia

Microsporidia are ubiquitous obligate eukaryotic intracellular parasites that are now felt to be more akin to degenerate fungi than to protozoa. Microsporidia can be highly pathogenic, causing a broad range of symptoms in humans, especially individuals who are immunocompromised. The vast majority of human cases of microsporidiosis have been reported during the past 20 years, in patients with HIV/AIDS, while only relatively rare cases have been described in immunocompetent individuals. However, microsporidia infections are being increasingly reported in patients following solid-organ transplanation, where the main symptom has been diarrhea. The authors report the first case of pulmonary microsporidial infection in an allogeneic bone marrow transplant recipient in the United States and only the second case in the world. The patient, with a history of Hodgkin disease followed by acute myelogenous leukemia received a T-cell-depleted graft, but succumbed to respiratory failure 63 days post transplantation. An open lung biopsy, taken just before death, was originally thought to show toxoplasmosis. The correct diagnosis of microsporidiosis was made postmortem by light and electron microscopy. DNA polymerase chain reaction analysis confirmed the diagnosis and furthermore revealed it to be the dog strain of the microsporidia species Encephalitozoon cuniculi. Although to date rarely diagnosed, microsporidial infection should also be considered in the differential diagnosis of, e.g., unexplained pulmonary infection in bone marrow transplant patients.

Uptake of Encephalitozoon spp. and Vittaforma corneae (Microsporidia) by different cells

Microsporidia are obligate intracellular parasites infecting a broad range of vertebrates and invertebrates. Various microsporidian species induce different clinical pictures in humans. The reason for this is not clear. It has been speculated that the different microsporidian species are transmitted by various routes, thus causing infections in different organs. Another possibility is that the diverse microsporidia have different tropisms to organ-specific cells, thus causing various diseases. In this study, we investigated the uptake of microsporidian spores by different cells with an immunofluorescence staining technique to investigate whether there is a difference between microsporidian species as well as between different cells. Using this technique, we were able to distinguish between intra- and extracellular microsporidian spores. All examined cell lines were able to internalize microsporidian spores, but the extent of internalization differed significantly between the cells. Although the results showed some patterns that correlate with the distribution of the parasites in humans, the different clinical pictures cannot be sufficiently explained by this phenomenon, so it seems more likely that the various clinical manifestations caused by the different microsporidian species are a consequence of different infection routes rather than of different affinities of the microsporidian species to different cells.

The microsporidian polar tube: a highly specialised invasion organelle

All of the members of the Microsporidia possess a unique, highly specialised structure, the polar tube. This article reviews the available data on the organisation, structure and function of this invasion organelle. It was over 100 years ago that Thelohan accurately described the microsporidian polar tube and the triggering of its discharge. In the spore, the polar tube is connected at the anterior end, and then coils around the sporoplasm. Upon appropriate environmental stimulation the polar tube rapidly discharges out of the spore pierces a cell membrane and serves as a conduit for sporoplasm passage into the new host cell. The mechanism of germination of spores, however, remains to be definitively determined. In addition, further studies on the characterisation of the early events in the rupture of the anterior attachment complex, eversion of the polar tube as well as the mechanism of host cell attachment and penetration are needed in order to clarify the function and assembly of this structure. The application of immunological and molecular techniques has resulted in the identification of three polar tube proteins referred to as PTP1, PTP2 and PTP3. The interactions of these identified proteins in the formation and function of the polar tube remain to be determined. Data suggest that PTP1 is an O-mannosylated glycoprotein, a post-translational modification that may be important for its function. With the availability of the Encephalitozoon cuniculi genome it is now possible to apply proteomic techniques to the characterisation of the components of the microsporidian spore and invasion organelle.

Zoonotic potential of the microsporidia

Microsporidia are long-known parasitic organisms of almost every animal group, including invertebrates and vertebrates. Microsporidia emerged as important opportunistic pathogens in humans when AIDS became pandemic and, more recently, have also increasingly been detected in otherwise immunocompromised patients, including organ transplant recipients, and in immunocompetent persons with corneal infection or diarrhea. Two species causing rare infections in humans, Encephalitozoon cuniculi and Brachiola vesicularum, had previously been described from animal hosts (vertebrates and insects, respectively). However, several new microsporidial species, including Enterocytozoon bieneusi, the most prevalent human microsporidian causing human immunodeficiency virus-associated diarrhea, have been discovered in humans, raising the question of their natural origin. Vertebrate hosts are now identified for all four major microsporidial species infecting humans (E. bieneusi and the three Encephalitozoon spp.), implying a zoonotic nature of these parasites. Molecular studies have identified phenotypic and/or genetic variability within these species, indicating that they are not uniform, and have allowed the question of their zoonotic potential to be addressed. The focus of this review is the zoonotic potential of the various microsporidia and a brief update on other microsporidia which have no known host or an invertebrate host and which cause rare infections in humans.

Pulmonary infection with microsporidia after allogeneic bone marrow transplantation

Microsporidia are obligate, intracellular protozoal parasites that can be pathogenic in immunocompromised individuals. The majority of cases of microsporidiosis have been documented in patients with HIV, and only a few case reports exist of infection in solid organ transplant patients. We report the first case of pulmonary microsporidial infection in an allogeneic bone marrow transplant recipient in the US. The patient was a recipient of a T-cell-depleted graft who succumbed to complications from respiratory failure 63 days post transplant. The diagnosis was made post mortem by electron microscopy and confirmed with PCR. Although rare, microsporidial infection should be considered in the differential diagnosis of unexplained pulmonary infection in bone marrow transplant patients.

Microsporidia and acquired immunodeficiency syndrome

Microsporidia is a common term that has been used to refer to a group of eukaryotic, obligate intracellular protozoan parasites belonging to the phylum Microspora. They are important agricultural parasites, contaminating commercial insects; they are also important by infecting laboratory rodents, rabbits and primates. Ever since the early cases found by Magarino Torres, who reported the presence of Encephalitozoon in a patient suffering of a meningoencephalomyelitis, some human pathology caused by microsporidia has been described. However, only after the acquired immunodeficiency syndrome outbreak have these organisms appeared as significant etiological agents in different pathologies. Even so, they remain underestimated. In the present article, the importance of microsporidia for the human pathology in immunocompromised host has been stressed.

Mammalian microsporidiosis

The phylum Microspora contains a diverse group of single-celled, obligate intracellular protozoa sharing a unique organelle, the polar filament, and parasitizing a wide variety of invertebrate and vertebrate animals, including insects, fish, birds, and mammals. Encephalitozoon cuniculi is the classic microsporidial parasite of mammals, and encephalitozoonosis in rabbits and rodents has been and continues to be recognized as a confounding variable in animal-based biomedical research. Although contemporary research colonies are screened for infection with this parasite, E. cuniculi remains a cause of morbidity and mortality in pet and conventionally raised rabbits. In addition, E. cuniculi is a potential pathogen of immature domestic dogs and farm-raised foxes. The recent discovery and identification of Encephalitozoon intestinalis, Encephalitozoon hellem, and Enterocytozoon bieneusi, in addition to E. cuniculi, as opportunistic pathogens of humans have renewed interest in the Microspora. Veterinary pathologists, trained in the comparative anatomy of multiple animal species and infectious disease processes, are in a unique position to contribute to the diagnosis and knowledge of the pathogenesis of these parasitic diseases. This review article covers the life cycle, ultrastructure, and biology of mammalian microsporaidia and the clinical disease and lesions seen in laboratory and domestic animals, particularly as they relate to Encephalitozoon species. Human microsporidial disease and animal models of human infection are also addressed. Often thought of as rabbit pathogens of historical importance, E. cuniculi and the related mammalian microsporidia are emerging as significant opportunistic pathogens of immunocompromised individuals.

[Trichome staining method applied to stools from HIV-infected patients with diarrhea, for microsporidia investigation]

The microsporidia have been involved in several clinical manifestations in patients with AIDS, of whom diarrhoea is the commonest. The diagnosis of microsporidiasis depended on invasive procedures and the identification of the organisms is made by electron microscopy. The modified trichrome staining method allows that the diagnosis be made without such procedures by using light microscopy. In the present work, the modified trchrome method was applied in stools from 62 patients with diarrhoea, who had asymptomatic HIV infection or AIDS. Of the 62 samples analyzed, there was detection of microsporidial spores in one. This work confirms the existence of such protozoans in our patients, associated with manifestations of chronic diarrhoea in patients with AIDS who have severe immunodeficiency and ascertains that this staining method allows satisfactory identification of microsporidia from faeces, as well points out some directions to further studies.

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.

Flow cytometric analysis of microsporidia belonging to the genus Encephalitozoon

Flow cytometry was used in the identification of human microsporidia belonging to the genus Encephalitozoon. Microsporidian spores of Encephalitozoon hellem, E. cuniculi, and E. intestinalis were propagated in axenic cultures of monkey kidney E6 cells, purified with Percoll, and exposed to homologous and heterologous rabbit antiserum and monoclonal antibody prepared against E. hellem spores. After reaction to goat anti-rabbit immunoglobulin G (IgG) or goat anti-mouse IgG conjugated to fluorescein isothiocyanate, fluorescence histograms from gated data on light-scatter profiles showed that rabbit anti-E. hellem serum was reactive to E. hellem spores but also had cross-reactivity to spores of E. cuniculi and E. intestinalis. On the other hand, fluorescence histograms showed that rabbit anti-E. cuniculi and rabbit anti-E. intestinalis sera were reactive with homologous spores only. Monoclonal antibody prepared against E. hellem reacted only with spores of E. hellem. Neither the polyclonal antibodies nor the monoclonal antibodies reacted with Cryptosporidium parvum oocysts. Fluorescence histograms of spores treated with 10% formalin also showed reactivity, but the number of events in the most intense peaks of fluorescence was fewer (7 to 42%, depending on species) than the number of events in the most intense peaks of fluorescence for nontreated spores. By flow cytometry, formalin-treated and nontreated spores of Encephalitozoon were identified to the species level by using gated data on light-scatter profiles and analyzing the fluorescence histograms from the indirect immunofluorescence of the spores. Once a procedure is established for the isolation of Encephalitozoon spores from clinical specimens, identification of spores by flow cytometry may be useful not only for diagnosis but also for epidemiologic studies.

Disseminated Encephalitozoon (Septata) intestinalis infection in a patient with AIDS: novel diagnostic approaches and autopsy-confirmed parasitological cure following treatment with albendazole

Encephalitozoon intestinalis is a recently described microsporidian which causes intestinal and disseminated infections in severely immunocompromised patients with AIDS. Preliminary data suggest that albendazole can be an effective therapy for patients with E. intestinalis infection. However, relapses have been reported following treatment in some cases. These results were based upon examination of cytologic, biopsy, or stool samples with an inherent sampling bias. This report documents the first postmortem evaluation of a patient with E. intestinalis infection treated with albendazole. Antemortem microsporidial diagnosis was performed on nasal mucosal smear and duodenal biopsy specimens by electron microscopy and a newly developed indirect fluorescent-antibody method based upon in vitro cultivation of the organism. This case represents the initial report of using nasal cytologic specimens for ultrastructural and antibody-based species-level diagnosis of microsporidiosis. Following successful treatment of this infection with albendazole, the patient died of other causes. A thorough autopsy examination failed to reveal the presence of E. intestinalis in any tissue, providing confirmatory evidence for a complete parasitological cure with albendazole.

Short-term in vitro culture and molecular analysis of the microsporidian, Enterocytozoon bieneusi

The microsporidium, Enterocytozoon bieneusi, causes a severe, debilitating, chronic diarrhea in patients with the acquired immunodeficiency syndrome. Specific diagnosis of intestinal microsporidiosis, especially due to Enterocytozoon, is difficult and there is no known therapy that can completely eradicate this parasite. Preliminary studies indicate that a short term (about 6 months) in vitro culture of this parasite yielding low numbers of spores, may be established by inoculating human lung fibroblasts and/or monkey kidney cell cultures with duodenal aspirates and or biopsy from infected patients. The cultures may subsequently be used for the isolation and molecular analysis of parasite DNA.

In vitro culture and serologic and molecular identification of Septata intestinalis isolated from urine of a patient with AIDS

Microsporidian spores were identified, on the basis of Weber's staining, in urine, stool, nasal, and saliva samples of an AIDS patient with diarrhea, hematuria, dysuria, and dementia. Urine and stool samples contained numerous spores, whereas few spores were seen in the nasal and saliva samples. Spores were concentrated from urine samples and inoculated into monkey kidney cell (E6) monolayers. After 6 to 8 weeks of culture, infected E6 cells filled with spores as well as spores free in the culture supernatants were seen daily. Transmission electron microscopy revealed that all stages of the parasite (CDC:V297) developed within septated, honeycomb-shaped parasitophorous vacuoles. Indirect immunofluorescence and immunoblotting studies using rabbit anti-Encephalitozoon cuniculi, anti-Encephalitozoon hellem, and anti-CDC:V297 sera revealed that CDC:V297 reacted intensely with the homologous serum but minimally with the heterologous sera. DNA isolated from CDC:V297, when PCR amplified with E. hellem and E. cuniculi primers, did not produce the diagnostic bands of approximately 547 and approximately 549 bp characteristic of E. hellem and E. cuniculi, respectively. On the basis of these studies, we concluded that CDC:V297 fits the description of Septata intestinalis (A. Cali, D. P. Kotler, and J. M. Orenstein, J. Eukaryot, Microbiol. 40:101-112, 1993).

Human microsporidiosis: Clinical, diagnostic and therapeutic aspects of an increasing infection

Human microsporidiosis is a parasitic infection due to species of four different genera: Encephalitozoon; Enterocytozoon; Nosema; and Pleistophora. Although well known as a cause of disease in animals, microsporidiosis was only occasionally reported in humans. Recently, in human immunodeficiency virus (HIV)-infected patients, microsporidia belonging to Encephalitozoon and Enterocytozoon species have proved to be important opportunistic pathogens. Enterocytozoon bieneusi is associated with chronic intermittent diarrhea, cholangiopathy and sinusitis whereas Encephalitozoon intestinalis, Encephalitozoon hellem and Encephalitozoon cuniculi, the three Encephalitozoon species found in humans, are associated with diarrhea, rhinosinusitis, keratoconjunctivitis, nephritis and hepatitis. Diagnosis of microsporidial infections in humans was until recently an invasive, laborious procedure including electron microscopy of small intestine biopsies. However, new simple staining methods using Uvitex 2B or modified trichrome stain for feces and other body fluids have facilitated clinical diagnosis as well as drug evaluation and epidemiological studies. The application of monoclonal antibodies and molecular techniques such as the polymerase chain reaction have further improved microsporidial diagnosis. Treatment of Entero. bieneusi has, until now, been unsuccessful whereas albendazole has proved to be an effective treatment for Encephalitozoon species infection. Identification of effective treatment for Entero. bieneusi infections and further study of the pathogenicity of these microsporidial infections in immunocompetent hosts are important future challenges.

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.

Bronchoscopic diagnosis of pneumonia

Lower respiratory tract infections are characterized by significant morbidity and mortality but also by a relative inability to establish a specific etiologic agent on clinical grounds alone. With the recognized shortcomings of expectorated or aspirated secretions toward establishing an etiologic diagnosis, clinicians have increasingly used bronchoscopy to obtain diagnostic samples. A variety of specimen types may be obtained, including bronchial washes or brushes, protected specimen brushings, bronchoalveolar lavage, and transbronchial biopsies. Bronchoscopy has been applied in three primary clinical settings, including the immunocompromised host, especially human immunodeficiency virus-infected and organ transplant patients; ventilator-associated pneumonia; and severe, nonresolving community- or hospital-acquired pneumonia in nonventilated patients. In each clinical setting, and for each specimen type, specific laboratory protocols are required to provide maximal information. These protocols should provide for the use of a variety of rapid microscopic and quantitative culture techniques and the use of a variety of specific stains and selective culture to detect unusual organism groups.

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.