Human microsporidial infections

Opportunistic properties of Nosema algerae (Microspora), a mosquito parasite, in immunocompromised mice

In the last ten years microsporidia have been recognized as opportunistic pathogens in AIDS patients. The sources of infection and the mechanisms of transmission of these organisms in humans are mostly uncertain. Transmission of invertebrate microsporidia to mammals is normally considered impossible, temperature being a limiting factor for development. Mice treated with cortisone acetate and with cyclosporin A, respectively, as well as athymic nice were injected intravenously, intranasally, perorally and subcutaneously with spores of Nosema algerae, a microsporidian species of culicine mosquitoes. No infection could be detected in tissue samples of cortisone acetate and cyclosporin A treated mice. However, the experimental inoculation of spores into the tail and foot of athymic mice caused severe infection in skeletal muscles and the connective tissue. In some tails, nerve tissue and bone marrow were also infected. Vegetative stages and spores were seen in direct contact to host cell cytoplasma. For the first time the prolonged and progressive development of an invertebrate microsporidium in a mammalian host is shown. The possibility of invertebrate microsporidia as a source of human microsporidiosis should now be taken into consideration.

Identification of an Enterocytozoon bieneusi-like microsporidian parasite in simian-immunodeficiency-virus-inoculated macaques with hepatobiliary disease

Enterocytozoon bieneusi is a common opportunistic pathogen of human patients with acquired immune deficiency syndrome (AIDS) causing significant morbidity and mortality. In a retrospective analysis utilizing conventional histochemical techniques, in situ hybridization, polymerase chain reaction, and ultrastructural examination, we identified 18 simian-immunodeficiency-virus-infected macaques (16 Macaca mulatta, 1 M. nemestrina, and 1 M. cyclopis) with Enterocytozoon infection of the hepatobiliary system and small intestine. The organisms were readily identified in the bile ducts and gall bladder by special stains and by in situ hybridization using a probe directed against the small subunit ribosomal RNA of human origin E. bieneusi. Infection of the biliary system was associated with a nonsuppurative and proliferative cholecystitis and choledochitis. Hepatic involvement was characterized by bridging portal fibrosis and nodular hepatocellular regeneration accompanied by marked bile ductular and septal duct hyperplasia. Ultrastructurally, all developmental stages of the organism were found in direct contact with the host cell cytoplasm; spores and sporoblasts contained a double layer of polar tubes. Sequencing of a 607-bp segment of the small subunit ribosomal RNA revealed 97 and 100% identity to two clones of small subunit ribosomal RNA derived from E. bieneusi of human origin. Extensive morphological and genetic similarities between the simian and human enterocytozoons suggest that experimentally infected macaques may serve as a useful model of microsporidial infection in AIDS.

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.

Pulmonary microsporidiosis due to Encephalitozoon hellem in a patient with AIDS

The microsporidian Encephalitozoon hellem is being reported with increasing frequency in HIV-positive subjects, as an agent of disseminated microsporidiosis without involving the gastrointestinal tract. We describe a case of pulmonary microsporidiosis in a 27-year-old Italian man with AIDS who developed fever, cough, and dyspnea. A chest X-ray showed multiple bilateral pulmonary opacities and mediastinal lymph-node enlargement. Stained smears of bronchoalveolar lavage sediment showed oval structures consistent with microsporidian spores. Viral, bacterial and fungal cultures were repeatedly negative, whereas microsporidia were successfully cultured in human and bovine fibroblast cell lines. Analysis of electron micrographs indicated that the isolate belonged to the genus Encephalitozoon. Based on further immunological, biochemical and molecular studies it was characterized as E. hellem. Even though a temporary improvement with albendazole therapy was noticed, the patient deteriorated clinically and died of severe respiratory distress.

Parasites and Diarrhea. I: Protozoans and Diarrhea

Intestinal parasitism is extremely common, with approximately 70% of all people harboring one or more intestinal parasite. Parasitism and diarrhea are both hyperendemic in areas where sanitation is suboptimal. Many clinicians assume that the identification of intestinal parasites in patients with diarrhea implies that the parasites are the cause. This approach is frequently misguided. Some intestinal parasites such as Giardia lamblia and Entamoeba histolytica certainly do cause diarrhea. Others, for example Entamoeba coli and Ascaris lumbricoides, almost certainly do not. In addition, there are a number of other organisms that have been associated with diarrheal illness in some cases, which may or may not be important pathogens. In this article, we will review the role of protozoans as definite and possible causes of diarrhea. In Part II, we review the role of helminths in diarrhea.

Agents of diarrhea

Diarrhea is a common problem for AIDS patients, and is chronic and debilitating. A thorough evaluation will reveal a pathogen in the majority of patients, and the organisms most frequently identified in AIDS patients with chronic diarrhea are Cryptosporidium, microsporidia, and Mycobacterium avium complex. Bacterial pathogens are more common in AIDS patients than in the general population and may present in different ways from infections in immunocompetent hosts. Other pathogens, including Cryptosporidium and microsporidia, are difficult to diagnose and have no effective therapy. Moreover, enteric viruses and HIV itself may contribute to the diarrhea. In addition to microbes, other factors such as medication, immune dysregulation, automatic dysfunction, and nutritional supplementation play a substantial role in diarrhea of AIDS patients.

A new acid-fast trichrome stain for simultaneous detection of Cryptosporidium parvum and microsporidial species in stool specimens

The detection in stool specimens of Cryptosporidium parvum and microsporidia, the most frequent parasitic pathogens causing diarrhea in AIDS patients, until now has depended on two different staining methods. However, since double infections occur and minimization of laboratory costs is mandatory, development of a method for simultaneous detection of these parasites appeared desirable. We report on a new, inexpensive, and easy-to-perform staining procedure to demonstrate both acid-fast oocysts of C. parvum and other coccidia, as well as microsporidial spores. This acid-fast trichrome stain yields results comparable to those obtained by the Kinyoun and modified trichrome methods and considerably reduces the time necessary for microscopic examination.

Gastrointestinal manifestations

Gastrointestinal disease is a common problem in the setting of HIV-1 infection. As patients live longer and other opportunistic pathogens are suppressed, these problems are becoming even more important in the quality of life.

A microsporidian isolated from an AIDS patient corresponds to Encephalitozoon cuniculi III, originally isolated from domestic dogs

The ribosomal DNA internal transcribed spacer (ITS) region of a recently cultured human Encephalitozoon cuniculi isolate was analyzed by gene amplification and DNA sequencing. Restriction endonuclease digestion (FokI) and double-stranded DNA heteroduplex mobility shift analysis were performed to determine their utility for strain differentiation. The human E. cuniculi isolate was identical to E. cuniculi III, which had been isolated only from domestic dogs until now. The patient providing the isolate owned a pet dog, but no microsporidia were detected in the pet's urine.

Detection of infection or infectious agents by use of cytologic and histologic stains

A wide variety of stains are useful for detection of different organisms or, for viruses, the cytopathologic changes they induce, in smears prepared directly from clinical specimens and in tissue sections. Other types of stains, such as hematoxylin and eosin, are used routinely to stain tissue sections and are most valuable for assessing the immunologic response of the host to the invading pathogen. In many cases, the pattern of inflammation provides important clues to diagnosis and helps to guide the selection of additional "special" stains used predominantly for diagnosis of infectious diseases. A stain may be nonspecific, allowing detection of a spectrum of organisms, as do the Papanicolaou stain and silver impregnation methods, or detection of only a limited group of organisms, as do the different acid-fast techniques. Some nonspecific stains, such as the Gram stain, are differential and provide valuable preliminary information concerning identification. Immunohistochemical stains, on the other hand, are specific for a particular organism, although in some cases cross-reactions with other organisms occur. Despite the wealth of information that can be gleaned from a stained smear or section of tissue, however, the specific etiology of an infection often cannot be determined on the basis of only the morphology of the organisms seen; culture data are essential and must be considered in the final diagnosis.

Microsporidial keratoconjunctivitis caused by Septata intestinalis in a patient with acquired immunodeficiency syndrome

PURPOSE

To examine and treat a patient with acquired immunodeficiency syndrome (AIDS) who had mildly hyperemic conjunctiva and epithelial keratopathy in both eyes.

METHODS

The patient underwent conjunctival biopsy. The specimen was examined by transmission electron microscopy.

RESULTS

Septata intestinalis was demonstrated to be the cause of keratoconjunctivitis in the patient. The keratoconjunctivitis resolved after three weeks of therapy with topical fumagillin. No organisms were seen on repeat conjunctival biopsy.

CONCLUSIONS

Microsporidial keratoconjunctivitis in patients with AIDS can be caused by S. intestinalis. This condition appears to respond to topical fumagillin.

Microsporidian spore wall: ultrastructural findings on Encephalitozoon hellem exospore

A study of the spore wall of Encephalitozoon hellem was performed on thin sections, freeze-fracture, and deep-etched samples to obtain information on spore wall organization and composition. Our observations demonstrate that the spore wall is formed by an inner 30-35 nm electron-lucent endospore and an outer 25-30 nm electron-dense exospore. The exospore is a complex of three layers: an outer spiny layer, an electron-lucent intermediate lamina and an inner fibrous layer. Freeze-fracture and deep-etching techniques reveal that the intermediate lamina and the inner fibrous layer result from the different spatial disposition of the same 4-nm thick fibrils. In thin sections the endospore reveals a scattered electron-dense material that appears in the form of trabecular structures when analyzed in deep-etched samples. The presence of chitin in the exospore is discussed.

Infectious gastroenterocolitides in children: an update on emerging pathogens

The recognition that bacterial infections induce signal transduction responses in infected epithelial cells also provides new avenues to consider as novel forms of therapy. For example, the chemokine interleukin-8, which attracts neutrophils to sites of mucosal infection, is produced by epithelial cells of gastric and intestinal origin in response to bacterial infection. Inhibitors of chemokine production or inhibition of the biologic effects of neutrophil chemoattractants have the potential to reduce both mucosal inflammatory responses and the attendant clinical sequelae. Eukaryotic cells also respond to infection with elevations in cytosolic second messengers, including inositol triphosphate (IP3) and calcium ([Ca2+]i). In intestinal epithelium, these second messengers can mediate the diarrheal response to infection. Calcium/calmodulin inhibitors may have a beneficial effect in treating those gastrointestinal infections mediated through changes in the level of cytosolic free calcium. DuPont and colleagues showed, for example, that oral therapy with zaldaride maleate relieves symptoms of disease and shortens the duration of diarrhea in travelers with ETEC-induced diarrhea. Evaluation of additional signal transduction responses to microbial infections should provide both new insights into the pathogenesis of gastrointestinal infectious diseases and novel approaches to consider for the prevention and therapy for these human illnesses.

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.

Sensitive PCR diagnosis of Infections by Enterocytozoon bieneusi (microsporidia) using primers based on the region coding for small-subunit rRNA

Enterocytozoon bieneusi is the most common microsporidian infecting patients with AIDS. We have developed a PCR primer pair, named EBIEF1/EBIER1, based on the small-subunit rRNA sequence of this microsporidian. Compared with other PCR-based methods, this primer pair shows a higher efficiency of detection in diagnostic applications than does another previously described primer pair, V1/EB450.

Intestinal microsporidiosis in HIV-positive patients with chronic unexplained diarrhea in Rio de Janeiro, Brazil: diagnosis, clinical presentation and follow-up

After the diagnosis of two cases of microsporidial intestinal infection in 1992, in Rio de Janeiro, we have started looking for this parasite in HIV-infected patients with chronic unexplained diarrhea. We have studied 13 patients from Hospital Evandro Chagas, IOC-FIOCRUZ. Fecal specimens from these patients were examined for the presence of Cryptosporidia and Microsporidia, in addition to routine examination. Spores of Microsporidia were found in the stools of 6 (46.1%) of the 13 patients studied, with 2 histological jejunal confirmations. The Microsporidia-infected patients presented chronic diarrhea with about 6 loose to watery bowel movements a day. Five infected patients were treated with Metronidazole (1.5 g/day). They initially showed a good clinical response, but they never stopped eliminating spores. After about the 4th week of therapy, their diarrhea returned. Two patients utilized Albendazole (400 mg/day-4 weeks) with a similar initial improvement and recurrence of the diarrhea. Intestinal Microsporidiosis seems to be a marker of advanced stages of AIDS, since 5 of our 6 infected patients were dead after a 6 month period of follow-up. The present study indicates that intestinal microsporidiosis may be a burgeoning problem in HIV-infected patients with chronic diarrhea in Brazil, which deserves further investigation.

Application of molecular techniques to the diagnosis of microsporidial infection

Microsporidia are now recognized as important pathogens of AIDS patients; the ability of these parasites to cause disease in immunocompetent persons is still being elucidated. Improved diagnostic tests for microsporidial infection are continually being sought for establishing diagnosis in order to avoid laborious electron microscopy studies that require invasively acquired biopsy specimens. Modified trichrome or chemofluorescent stains are useful for detecting microsporidia in bodily fluids and stool specimens, but they do not allow for speciation of microsporidia. Polymerase chain reaction with specific primers will allow the detection and speciation of microsporidia in biopsy tissue, bodily fluids, and stool specimens.

Characterization of Encephalitozoon (Septata) intestinalis isolates cultured from nasal mucosa and bronchoalveolar lavage fluids of two AIDS patients

Microsporidia are obligate intracellular protozoan parasites that can cause opportunistic infections in AIDS patients. Species from five genera of microsporidia are presently known to infect man. One species, Septata intestinalis originally was detected in stool specimens of individuals with chronic diarrhea and subsequently was found to disseminate to the kidneys, lungs, and nasal sinuses. This organism has since been reclassified as Encephalitozoon and in this study, we report the culture of Encephalitozoon intestinalis from a bronchoalveolar lavage specimen and a nasal mucus aspirate of two AIDS patients living in the USA. The bronchoalveolar and nasal microsporidian isolates grew in several continuous cell lines including RK-13, MDCK, HT-29, Caco-2, Vero, and I047. Transmission electron microscopy of the clinical and cell culture specimens revealed that the new isolates appeared to be E. intestinalis based on morphology and growth of organisms in septated membrane-bound parasitophorous vacuoles. The new E. intestinalis isolates were characterized and compared with the first isolated E. intestinalis that was cultured from stool to confirm their identity and to determine if there existed any minor differences, as seen in the closely related Encephalitozoon cuniculi strains. By the methods of sodium dodecyl sulfate-polyacrylamide gel electrophoresis staining for proteins and carbohydrates, Western blot immunodetection, and polymerase chain reaction-based methods with restriction endonuclease digestion, double-stranded DNA heteroduplex mobility shift analysis, and DNA sequencing of the ribosomal DNA intergenic spacer region, the new isolates were identical to each other and to the reference isolate of E. intestinalis. In addition, with any of these methods, the E. intestinalis organisms could be distinguished from the three E. cuniculi strains, Encephalitozoon hellem, and Vittaforma corneae, which is important for diagnostics, therapeutic strategies, and epidemiology.

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.

Identification and characterization of three Encephalitozoon cuniculi strains

Microsporidia are increasingly recognized as causing opportunistic infections in immunocompromised individuals. Encephalitozoon cuniculi is probably the most studied mammalian microsporidian that infects insects and mammals, including man. In this study, 8 E. cuniculi isolates were compared and were found to fall into 3 strains. Strain type I includes the rabbit type isolate, as well as isolates from an additional rabbit, a dwarf rabbit, and a mouse. Strain type II includes 2 murine isolates and strain type III includes 2 isolates obtained from domestic dogs. By SDS-PAGE, the 3 strains differ primarily in the molecular weight range of 54-59 kDa where strain type I displays an apparent broad singlet at 57 kDa, strain type II displays an apparent doublet at 54 and 58 kDa, and strain type III displays an apparent broad band at 59 kDa. Antigenic differences were detected in the molecular weight regions of 54-58 kDa as well as 28-40 kDa by Western blot immunodetection using murine antisera raised against E. cuniculi, Encephalitozoon hellem, and the Encephalitozoon-like Septata intestinalis. Polymerase chain reaction (PCR) products containing only small subunit rDNA sequences from the different E. cuniculi isolates formed homoduplexes whereas PCR products containing intergenic rRNA gene sequences formed heteroduplexes in mobility shift analyses. Fok I digestion of the PCR products containing the intergenic rRNA gene region resulted in unique restriction fragment length polymorphism patterns, and DNA sequencing demonstrated that in the intergenic spacer region, the sequence 5'-GTTT-3' was repeated 3 times in strain type I, twice in strain type II, and 4 times in strain type III. This study indicates that there exist at least 3 E. cuniculi strains which may become important in the epidemiology of human E. cuniculi infections. Furthermore, as additional E. cuniculi isolates are characterized, these strains will be named or reclassified once the criteria for taxonomy and phylogenetic tree construction for microsporidia become better defined.

Tissue diagnosis of intestinal microsporidiosis using a fluorescent stain with Uvitex 2B

AIMS

To detect intestinal microsporidiosis in paraffin wax embedded biopsy specimens using a fluorescence technique incorporating optical brighteners.

METHODS

Eight HIV infected patients with confirmed intestinal microsporidiosis (six with Enterocytozoon bieneusi, one with Encephalitozoon intestinalis and one with Encephalitozoon cuniculi infection) and 10 without infection were studied. Tissue sections of paraffin wax embedded duodenal biopsy specimens were stained with 1% Uvitex 2B, coded and analysed independently by two investigators.

RESULTS

In all eight cases with confirmed intestinal microsporidian infection, spores could be detected easily in tissue sections using the fluorescence technique. Spores or other elements consistent with microsporidiosis were not found in the 10 patients without infection.

CONCLUSION

Staining of tissue sections from paraffin wax embedded intestinal biopsy specimens with stains incorporating Uvitex 2B is a rapid and easy technique for the diagnosis of intestinal microsporidiosis.

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.

Detection of microsporidia (Enterocytozoon bieneusi) in intestinal biopsy specimens from human immunodeficiency virus-infected patients by PCR

Intestinal microsporidiosis has been implicated as a major cause of chronic diarrhea in human immunodeficiency virus (HIV)-infected patients. So far diagnosis depends on direct visualization of the parasites by light and transmission electron microscopy. We evaluated the diagnostic value of microsporidian DNA amplification by PCR on duodenal biopsy specimens obtained from patients with and without intestinal microsporidiosis caused by Enterocytozoon bieneusi. Thirteen HIV-infected patients (all CDC stage C3) were studied. Eight patients had intestinal microsporidiosis caused by E. bieneusi (n = 6), Septata intestinalis (n = 1), and Encephalitozoon cuniculi (n = 1); microsporidioses were diagnosed by light microscopy of stool samples and confirmed by light and electron microscopy of intestinal biopsy specimens. Five patients had no microsporidia in their stool samples or in their intestinal biopsy specimens, as examined by light and electron microscopy. Additionally, DNA prepared from Toxoplasma gondii derived from mouse ascites was used as a further control. A 353-bp DNA fragment of the small-subunit rRNA gene could be amplified from all six biopsy specimens infected with E. bieneusi, and the nature of the PCR products was confirmed by Southern blot hybridization. No amplification of DNA fragments was seen by using DNA extracted from biopsy specimens with S. intestinalis or E. cuniculi infection or without microsporidian infection and with template DNA extracted from T. gondii. The results suggest that PCR testing of intestinal biopsy specimens may be a useful approach to diagnosing microsporidiosis in HIV-infected patients.

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.

Reactive nitrogen intermediates implicated in the inhibition of Encephalitozoon cuniculi (phylum microspora) replication in murine peritoneal macrophages

Encephalitozoon cuniculi (phylum microspora) is a protozoan parasite that can replicate within parasitophorous vacuoles in macrophages. Thioglycollate-elicited BALB/c peritoneal macrophages treated with murine recombinant interferon-gamma (rIFN-gamma; 100 7/ml) in combination with lipopolysaccharide (LPS; 10 ng/ml) for 24 h killed E. cuniculi as determined by significant reductions in the number of parasites and percent of infected macrophages 48 h later compared with cultures treated with medium only. Treatment of the elicited macrophages with murine rIFN-gamma (10 u/ml or 100 u/ml) only, resulted in microbistatic activity. Significantly higher levels of nitrite (NO2) were detected in supernatants from macrophage cultures treated with rIFN-gamma (10 u/ml or 100 u/ml) which induced microbistatic macrophage activity as well as from macrophage cultures treated with LPS + rIFN- when compared with levels of nitrite detected in supernatants of infected macrophages treated with medium only. Addition of the L-arginine analogue, N3 monomethyl-L-arginine (NMMA) at concentrations of 50, 100 or 250 uM significantly inhibited nitrite synthesis and prevented microsporidia killing. Addition of exogenous L-arginine at concentrations of 5 mM or 10 mM reversed the NMMA-induced inhibition of parasite killing. These results indicate that reactive nitrogen intermediates contribute to the killing of E. cuniculi by LPS + rIFN-gamma-activated murine peritoneal macrophages in vitro.

Human antiprotozoal therapy: past, present, and future

Human protozoal infections are ubiquitous and occur worldwide. In many cases, antiprotozoal agents currently in use predate the modern antibiotic era. Despite the relative lag in development of new antiprotozoal agents, the 1990s have witnessed an increasing level of interest in these infections, inspired by international travel and immigration, a growing awareness of antiprotozoal drug resistance, and the significance of acute and recrudescent protozoal infections in immunosuppressed hosts. This review summarizes for nonclinician readers the past, present, and future therapies for common human protozoal infections, as well as pharmacologic mechanisms of action and resistance and common toxicities associated with these agents.

Identification of microsporidia in stool specimens by using PCR and restriction endonucleases

We report the development of a PCR-based assay for the detection of microsporidia in clinical specimens. A single primer pair complementary to conserved sequences of the small-subunit rRNA enabled amplification of DNA from the four major microsporidian pathogens of humans: Encephalitozoon cuniculi, Encephalitozoon hellem, Enterocytozoon bieneusi, and Septata intestinalis. The extraction method allowed PCR amplification of E. bieneusi and S. intestinalis DNA from sodium hypochlorite-treated stool specimens. Differentiation of the microsporidian gastrointestinal pathogens E. bieneusi and S. intestinalis could be accomplished by restriction endonuclease digestion of PCR products using PstI and HaeIII.

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).