Potential efficacy of fumagillin in intestinal microsporidiosis due to Enterocytozoon bieneusi in patients with HIV infection: results of a drug screening study. The French Microsporidiosis Study Group

Current Therapy and Therapeutic Targets for Microsporidiosis

Microsporidia are obligate intracellular, spore-forming parasitic fungi which are grouped with the Cryptomycota. They are both opportunistic pathogens in humans and emerging veterinary pathogens. In humans, they cause chronic diarrhea in immune-compromised patients and infection is associated with increased mortality. Besides their role in pébrine in sericulture, which was described in 1865, the prevalence and severity of microsporidiosis in beekeeping and aquaculture has increased markedly in recent decades. Therapy for these pathogens in medicine, veterinary, and agriculture has become a recent focus of attention. Currently, there are only a few commercially available antimicrosporidial drugs. New therapeutic agents are needed for these infections and this is an active area of investigation. In this article we provide a comprehensive summary of the current as well as several promising new agents for the treatment of microsporidiosis including: albendazole, fumagillin, nikkomycin, orlistat, synthetic polyamines, and quinolones. Therapeutic targets which could be utilized for the design of new drugs are also discussed including: tubulin, type 2 methionine aminopeptidase, polyamines, chitin synthases, topoisomerase IV, triosephosphate isomerase, and lipase. We also summarize reports on the utility of complementary and alternative medicine strategies including herbal extracts, propolis, and probiotics. This review should help facilitate drug development for combating microsporidiosis.

Safety and efficacy of fumagillin for the treatment of intestinal microsporidiosis. A French prospective cohort study

BACKGROUND

Intestinal microsporidiosis due to Enterocytozoon bieneusi is a cause of chronic diarrhoea in immunocompromised patients. Fumagillin has been approved in France for its treatment.

OBJECTIVES

To investigate the efficacy and safety of fumagillin in a real-life setting.

METHODS

As required by the French Medicine Agency, all patients receiving fumagillin were enrolled in a prospective study to evaluate its efficacy and safety. Stool examination with identification of E. bieneusi by PCR was performed at baseline, end of treatment and monthly thereafter for 6 months. Safety was monitored up to 6 months and full blood counts were monitored up to 42 days after treatment initiation. The primary endpoint was safety. Parasite clearance and relapses were secondary endpoints.

RESULTS

From 2007 to 2018, 166 patients received fumagillin, including 6 children. Patients were transplant recipients (84%), HIV-infected patients (13%) or had another cause of immunosuppression (5%). Serious adverse events were reported in 41 patients (25%), mainly thrombocytopenia (15%) and neutropenia (5%), with two haemorrhagic events leading to one death. Severe thrombocytopenia (<50 G/L) developed in 50 patients (29.6%), neutropenia (<1 G/L) in 20 patients (11.8%) and severe anaemia (<8 g/dL) in 21 patients (12.4%). At the end of treatment, 94% of patients with available stool examination (n = 132) had no spores detected. Among 99 patients with available follow-up after the end of treatment, three parasite relapses were documented.

CONCLUSIONS

E. bieneusi microsporidiosis was mainly diagnosed in transplant recipients. Fumagillin was associated with haematological toxicity but showed high efficacy with a low relapse rate.

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.

Ecological and public health significance of Enterocytozoon bieneusi

Enterocytozoon bieneusi, a fungus-like protist parasite, causes symptomatic and asymptomatic intestinal infections in terrestrial animals and is also abundant in the environment. This parasite has been isolated from a variety of host types including humans, livestock, companion animals, birds, and wildlife, as well as the natural and urban environments including drinking source water, coastal water, recreational water, wastewater, vegetables in retail markets, and raw milk on farms. E. bieneusi exhibits high genetic diversity among host species and environmental sources and at least 500 genotypes have been identified thus far. Since its discovery in AIDS patients in 1985, scientists across the world have worked to demonstrate the natural history and public health potential of this pathogen. Here we review molecular typing studies on E. bieneusi and summarize relevant data to identify the potential sources of human and nonhuman infections and environmental contamination. This review also discusses the possible transmission routes of E. bieneusi and the associated risk factors, and advocates the importance of the One Health approach to tackle E. bieneusi infections.

Fumagillin, a Mycotoxin of Aspergillus fumigatus: Biosynthesis, Biological Activities, Detection, and Applications

Fumagillin is a mycotoxin produced, above all, by the saprophytic filamentous fungus Aspergillus fumigatus. This mold is an opportunistic pathogen that can cause invasive aspergillosis, a disease that has high mortality rates linked to it. Its ability to adapt to environmental stresses through the production of secondary metabolites, including several mycotoxins (gliotoxin, fumagillin, pseurotin A, etc.) also seem to play an important role in causing these infections. Since the discovery of the A. fumigatus fumagillin in 1949, many studies have focused on this toxin and in this review we gather all the information currently available. First of all, the structural characteristics of this mycotoxin and the different methods developed for its determination are given in detail. Then, the biosynthetic gene cluster and the metabolic pathway involved in its production and regulation are explained. The activity of fumagillin on its target, the methionine aminopeptidase type 2 (MetAP2) enzyme, and the effects of blocking this enzyme in the host are also described. Finally, the applications that this toxin and its derivatives have in different fields, such as the treatment of cancer and its microsporicidal activity in the treatment of honeybee hive infections with Nosema spp., are reviewed. Therefore, this work offers a complete review of all the information currently related to the fumagillin mycotoxin secreted by A. fumigatus, important because of its role in the fungal infection process but also because it has many other applications, notably in beekeeping, the treatment of infectious diseases, and in oncology.

Intestinal microsporidiosis in Strasbourg from 2014 to 2016: emergence of an Enterocytozoon bieneusi genotype of Asian origin

Microsporidia cause opportunistic infections in highly immunodeficient individuals. Few studies on the epidemiology of these infections have been conducted in France. Between 2014 and 2016, we undertook a study to estimate the prevalence and circulating genotypes of this fungus-related micro-organism among the population of Strasbourg University Hospital. Samples were collected from hospitalized patients and analyzed using microscopy and molecular assays. Strains from positive subjects were sequenced for genotyping. Only 7/661 patients (1.1%) were positive for microsporidia, and the only species identified was Enterocytozoon bieneusi. Two patients presented immunodeficiency linked to AIDS, and five transplant recipients presented immunodeficiency linked to immunosuppressive therapies. Only five patients received specific antimicrosporidial treatment, but clinical outcomes were good in all cases. We identified four genotypes: A and D in patients with AIDS, and C and S9 in transplant recipients. To date, genotype S9 has been described only once. This genotype is similar to those found in farm animals in China. Because some of these animals have been introduced to Central Europe, we postulate that this genotype might be of Asian origin. Thus, genotyping microsporidial strains may be of epidemiological and clinical interest to identify potential outbreak sources depending on the infecting strains.

Effects of selected Indonesian plant extracts on E. cuniculi infection in vivo

The present study was conducted to evaluate the methanolic extracts from several plant leaves widely used in traditional medicine to cure digestive tract disorders and in the self-medication of wild animals such as non-human primates, namely Archidendron fagifolium, Diospyros sumatrana, Shorea sumatrana, and Piper betle leaves, with regard to their antimicrosporidial activity against Encephalitozoon cuniculi in immunocompetent BALB/c mice determined using molecular detection of microsporidial DNA (qPCR) in various tissues and body fluids of infected, treated mice. Of the plant extracts tested, Diospyros sumatrana provided the most promising results, reducing spore shedding by 88% compared to untreated controls. Moreover, total burden per 1 g of tissue in the D. sumatrana extract-treated group reached 87% reduction compared to untreated controls, which was comparable to the effect of the standard drug, Albendazole. This data represents the baseline necessary for further research focused on determining the structure, activity and modes of action of the active compounds, mainly of D. sumatrana, enabling subsequent development of antimicrosporidial remedies.

Enterocytozoon bieneusi Identification Using Real-Time Polymerase Chain Reaction and Restriction Fragment Length Polymorphism in HIV-Infected Humans from Kinshasa Province of the Democratic Republic of Congo

Objective. To determine the prevalence and the genotypes of Enterocytozoon bieneusi in stool specimens from HIV patients. Methods. This cross-sectional study was carried out in Kinshasa hospitals between 2009 and 2012. Detection of microsporidia including E. bieneusi and E. intestinalis was performed in 242 HIV-infected patients. Typing was based on DNA polymorphism of the ribosomal DNA ITS region of E. bieneusi. PCRRFLP generated with two restriction enzymes (Nla III and Fnu 4HI) in PCR-amplified ITS products for classifying strains into different lineages. The diagnosis performance of the indirect immune-fluorescence-monoclonal antibody (IFI-AcM) was defined in comparison with real-time PCR as the gold standard. Results. Out of 242 HIV-infected patients, using the real-time PCR, the prevalence of E. bieneusi was 7.9% (n = 19) among the 19 E. bieneusi, one was coinfected with E. intestinalis. In 19 E. bieneusi persons using PCR-RFLP method, 5 type I strains of E. bieneusi (26.3%) and 5 type IV strains of E. bieneusi (26.3%) were identified. The sensitivity of IFI-AcM was poor as estimated 42.1%. Conclusion. Despite different PCR methods, there is possible association between HIVinfection, geographic location (France, Cameroun, Democratic Republic of Congo), and the concurrence of type I and type IV strains.

Fumagillin for treatment of intestinal microsporidiosis in renal transplant recipients

We report 10 cases of intestinal microsporidiosis due to Enterocytozoon bieneusi in renal transplant (RT) recipients who were treated with fumagillin. All patients presented with afebrile subacute diarrhea (median of 2 weeks), associated with abdominal cramps (n = 5), and weight loss (n = 6), a mean of 68 months after RT. The diagnosis was made by the identification of microsporidial spores in stools with the use of appropriate staining and confirmed by a specific polymerase chain reaction assay for E. bieneusi in 7 patients. Median CD4 cell count was 292 cells/mm(3). All patients received a median of 14 days of oral fumagillin (20 mg tid), and four patients also discontinued or tapered their immunosuppressive regimen (mycophenolate mofetil in 3, and azathioprine in 2). Clinical symptoms resolved rapidly with the clearance of microsporidial spores from stools in all patients. A severe but reversible thrombocytopenia was observed in one patient during fumagillin therapy, and another patient presented with abdominal cramps. Trough levels of tacrolimus measured in seven patients dropped below 5 ng/mL in six of them after 7-14 days of fumagillin. Intestinal microsporidiosis can cause subacute diarrhea in RT recipients. Fumagillin is an effective treatment with an acceptable safety profile, but monitoring of tacrolimus levels is warranted.

Clinical significance of enteric protozoa in the immunosuppressed human population

Globally, the number of immunosuppressed people increases each year, with the human immunodeficiency virus (HIV) pandemic continuing to spread unabated in many parts of the world. Immunosuppression may also occur in malnourished persons, patients undergoing chemotherapy for malignancy, and those receiving immunosuppressive therapy. Components of the immune system can be functionally or genetically abnormal as a result of acquired (e.g., caused by HIV infection, lymphoma, or high-dose steroids or other immunosuppressive medications) or congenital illnesses, with more than 120 congenital immunodeficiencies described to date that either affect humoral immunity or compromise T-cell function. All individuals affected by immunosuppression are at risk of infection by opportunistic parasites (such as the microsporidia) as well as those more commonly associated with gastrointestinal disease (such as Giardia). The outcome of infection by enteric protozoan parasites is dependent on absolute CD4(+) cell counts, with lower counts being associated with more severe disease, more atypical disease, and a greater risk of disseminated disease. This review summarizes our current state of knowledge on the significance of enteric parasitic protozoa as a cause of disease in immunosuppressed persons and also provides guidance on recent advances in diagnosis and therapy for the control of these important parasites.

Novel paradigms for drug discovery: computational multitarget screening

An established paradigm in current drug development is (i) to identify a single protein target whose inhibition is likely to result in the successful treatment of a disease of interest; (ii) to assay experimentally large libraries of small-molecule compounds in vitro and in vivo to identify promising inhibitors in model systems; and (iii) to determine whether the findings are extensible to humans. This complex process, which is largely based on trial and error, is risk-, time- and cost-intensive. Computational (virtual) screening of drug-like compounds simultaneously against the atomic structures of multiple protein targets, taking into account protein-inhibitor dynamics, might help to identify lead inhibitors more efficiently, particularly for complex drug-resistant diseases. Here we discuss the potential benefits of this approach, using HIV-1 and Plasmodium falciparum infections as examples. We propose a virtual drug discovery 'pipeline' that will not only identify lead inhibitors efficiently, but also help minimize side-effects and toxicity, thereby increasing the likelihood of successful therapies.

Therapeutic strategies for human microsporidia infections

Over the past 20 years, microsporidia have emerged as a cause of infectious diseases in AIDS patients, organ transplant recipients, children, travelers, contact lens wearers and the elderly. Enterocytozoon bieneusi and the Encephalitozoon spp., Encephalitozoon cuniculi, Encephalitozoon hellem and Encephalitozoon intestinalis, are the most frequently identified microsporidia in humans, and are associated with diarrhea and systemic disease. The microsporidia are small, single-celled, obligately intracellular parasites that have been identified in water sources, as well as in wild, domestic and food-producing farm animals, thereby raising concerns for waterborne, foodborne and zoonotic transmission. Current therapies for microsporidiosis include albendazole, a benzimidazole that inhibits microtubule assembly and is effective against several microsporidia, including the Encephalitozoon spp., although it is less effective against Encephalitozoon bieneusi. Fumagillin, an antibiotic and antiangiogenic compound produced by Aspergillus fumigatus, is more broadly effective against Encephalitozoon spp. and E. bieneusi; however, is toxic when administered systemically to mammals. Recent studies are also focusing on compounds that target the microsporidia polyamines (e.g., polyamine analogs), methionine aminopeptidase 2 (e.g., fumagillin-related compounds), chitin inhibitors (e.g., nikkomycins), topoisomerases (e.g., fluoroquinolones) and tubulin (e.g., benzimidazole-related compounds).

Pulmonary localization of Enterocytozoon bieneusi in an AIDS patient: case report and review

Enterocytozoon bieneusi is an agent of intestinal microsporidiosis leading to malabsorption syndrome and diarrhea in AIDS patients. Respiratory tract microsporidiosis due to Encephalitozoon spp. has been reported. To date, however, only two cases of pulmonary involvement of E. bieneusi have been documented for patients with intestinal microsporidiosis. We report here another pulmonary localization of E. bieneusi in a human immunodeficiency virus-infected patient. Clinical features of these three cases are reviewed. E. bieneusi can colonize the respiratory tract but could be considered a simple carriage associated with an intestinal infection.

HIV1 and the gut in the era of highly active antiretroviral therapy

The gut and its gut-associated lymphoid tissue serve as a preferential site for HIV1 entry, active viral replication, reservoir, and HIV-mediated CD4 cell apoptosis. The widespread use of highly active antiretroviral therapy (HAART) has resulted in a significant decrease in the incidence of opportunistic enteric pathogens as a consequence of immune recovery. Nonetheless, patients with advanced HIV1 disease who were recently diagnosed or have poor response to HAART can still suffer from opportunistic infections with pathogens such as Cryptosporidium, microsporidia, Isospora belli, Cyclospora cayetanensis, Mycobacterium avium complex, and cytomegalovirus, among others. This review describes the impact of HIV1 infection on gut immune function, the salient features of the most common opportunistic enteric pathogens and HIV-associated enteropathy, and the effects of immune reconstitution after introduction of HAART.

Criterion-related validity of a diarrhea questionnaire in HIV-infected patients

Clinical trials evaluating HIV-related diarrhea have used varied unidimensional end points to assess diarrhea severity. We hypothesized that a self-reported measure of diarrhea that assesses stool form, stool frequency, and diarrhea morbidity would accurately portray the severity of HIV-related diarrhea. During a clinical trial for HIV-related diarrhea, we evaluated the instrument among 17 patients, comparing survey results with objective measures of diarrhea morbidity recorded concurrently. The survey scores demonstrated consistently high Spearman correlations with nursing assessment of stool form (0.6693), observed stool frequency (0.7023), and cumulative stool weight (0.8216), all recorded over six days of intensive inpatient observation (P < 0.01 for each). Of the three components of the survey, only the stool form assessment, which uses pictorial representations of stool consistency, correlated significantly across all three objective measures (0.8069-0.8792). In demonstrating the concurrent, criterion-related validity of this survey, we found it helpful for evaluating HIV-related diarrhea and suggest its utility for HIV-seronegative subjects as well.

Fumagillin treatment of intestinal microsporidiosis

BACKGROUND

Intestinal microsporidiosis due to Enterocytozoon bieneusi is a cause of chronic diarrhea, malabsorption, and wasting in immunocompromised patients. Currently, there is no effective treatment.

METHODS

We conducted a randomized, double-blind, placebo-controlled trial of fumagillin (60 mg per day orally for two weeks) in patients with chronic E. bieneusi infection. Efficacy was assessed primarily by the clearance of microsporidia, as evidenced by analysis of stool specimens. Patients in whom microsporidia were not cleared received treatment for two weeks with open-label fumagillin. After clearance of the parasite, follow-up stool examinations were performed monthly to detect relapses.

RESULTS

Twelve patients were enrolled in this study, 10 with the acquired immunodeficiency syndrome and 2 who had received organ transplants. Clearance of microsporidia occurred in all six of the patients in the fumagillin group, as compared with none of the six in the placebo group (P=0.002). Treatment with fumagillin was also associated with increases in absorption of D-xylose (P=0.003) and in Karnofsky performance scores (P<0.001) and with decreases in loperamide use (P=0.01) and total stool weight (P=0.04). There were serious adverse events (neutropenia and thrombocytopenia) in three patients in the fumagillin group; one patient in the placebo group had severe diarrhea. All six controls subsequently had clearance of microsporidia after open-label treatment with fumagillin. Relapses of the infection were identified in two patients during follow-up (median follow-up, 10 months).

CONCLUSIONS

Fumagillin is an effective treatment for chronic E. bieneusi infection in immunocompromised patients.

Novel synthetic polyamines are effective in the treatment of experimental microsporidiosis, an opportunistic AIDS-associated infection

Microsporidia are eukaryotic obligate intracellular protists that are emerging pathogens in immunocompromised hosts, such as patients with AIDS or patients who have undergone organ transplantation. We have demonstrated in vitro and in vivo that synthetic polyamine analogs are effective antimicrosporidial agents with a broad therapeutic window. CD8-knockout mice or nude mice infected with the microsporidian Encephalitozoon cuniculi were cured when they were treated with four different novel polyamine analogs at doses ranging from 1.25 to 5 mg/kg of body weight/day for a total of 10 days. Cured animals demonstrated no evidence of parasitemia by either PCR or histologic staining of tissues 30 days after untreated control animals died.

Gastrointestinal infections in the immunocompromised host

The gastrointestinal tract is a common site of infection in the opportunistic host. Pathogens range from highly virulent organisms, which infect people with well functioning immune systems as well as people with poorly functioning immune systems, to opportunistic organisms, which infect only those with impaired immune systems. Viruses, bacteria, fungi, and protozoa lead to disease that can be especially severe, debilitating, and difficult to treat in the immunocompromised host. Yet in this era of highly active antiretroviral therapy for HIV-infected patients and strategies to reduce immunosuppression in transplant and oncology patients, appropriate diagnostic tests and treatment can both improve the quality of life and decrease mortality. In this article, I review the changing pathogenesis, epidemiology, clinical presentation, diagnosis, and treatment of gastrointestinal infections in the immunocompromised host.

Drug treatment of microsporidiosis

Microsporidia are ubiquitous organisms that are emerging pathogens in humans. These are most likely zoonotic and/or waterborne infections. In the immunosuppressed host, such as those treated with immunosuppressive drugs or infected with human immunodeficiency virus particularly at advanced stages of the disease, microsporidia can produce a wide range of clinical diseases. The most common manifestation is gastrointestinal tract infection; however, encephalitis, ocular infection, sinusitis, myositis and disseminated infection have also been described. In addition, these organisms have been reported in immune competent individuals. Multiple genera are involved in these infections and different organisms can result in distinct clinical pictures. Differences in clinical and parasitologic response to various therapeutic agents have emerged from clinical, as well as in vitro and in vivo studies. Currently there are no precisely defined guidelines for the optimal treatment of microsporidial infections. This article reviews the available data on compounds with in vitro activity and/or in vivo efficacy for microsporidial infections. Copyright 2000 Harcourt Publishers Ltd.

Trial of oral fumagillin for the treatment of intestinal microsporidiosis in patients with HIV infection. ANRS 054 Study Group. Agence Nationale de Recherche sur le SIDA

OBJECTIVE

Intestinal microsporidiosis caused by Enterocytozoon bieneusi is a cause of chronic diarrhoea in patients with HIV infection for which there is no current therapy. This study was designed to assess the safety and efficacy of oral fumagillin in this infection.

DESIGN

A dose-escalation trial.

METHODS

Twenty-nine HIV-infected patients with E. bieneusi infection were consecutively enrolled in the trial. Oral doses of fumagillin were given to four groups of patients for 14 days: 10 mg/day (group 1), 20 mg/day (group 2), 40 mg/day (group 3), and 60 mg/day (group 4). Patients were seen at weeks 1, 2, 4 and 6 to assess safety and efficacy. Efficacy was assessed primarily by the clearance of microsporidia from stools and follow-up duodenal biopsies.

RESULTS

Thirteen patients complained of abdominal cramps, vomiting or diarrhoea during the study, and three patients had fumagillin withdrawn because of adverse events. Thrombocytopenia, neutropenia and hyperlipasaemia were the most frequent biological adverse events. Twenty-one out of 29 patients transiently cleared microsporidia from their stools during the study. By week 6, however, all patients in groups 1, 2 and 3 had parasitic relapse. Interestingly, eight out of 11 (72%) patients treated with 60 mg/day (group 4) apparently cleared microsporidia from their gastrointestinal tract and gained weight. No parasitic relapse was documented in these eight patients during a mean follow-up of 11.5 months.

CONCLUSION

Treatment with fumagillin at 60 mg/day for 14 days has promise as an effective oral treatment for E. bieneusi infections.

Microsporidiosis in mammals

Microsporidia are small, single-celled, obligately intracellular parasites that have caused significant agricultural losses and interference with biomedical research. Interest in the microsporidia is growing, as these organisms are recognized as agents of opportunistic infections in persons with AIDS and in organ transplant recipients. Microsporidiosis is also being recognized in children and travelers, and furthermore, concern exists about the potential of zoonotic and waterborne transmission of microsporidia to humans. This article reviews the basic biology and epidemiology of microsporidiosis in mammals.

Electron microscopy as a tool for identifying new pathogens

Electron microscopy (EM) is still an important tool for the investigation of infectious diseases, despite the introduction of powerful new methods, mainly involving the polymerase chain reaction. Particularly in the field of parasitic protozoology associated with AIDS, where many new species of human pathogens have been recognized in tissue biopsies, EM remains an essential 'catch-all' diagnostic method. The resolved ultrastructural details of these newly recognized parasites allows a unique insight into the biology of these organisms. The information produced by EM is different, but complementary, to that provided by alternative methods.

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.

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.

Microsporidiosis in travelers with diarrhea from the tropics

BACKGROUND

Microsporidia are protozoa which mainly affect severely immunodepressed AIDS patients in developed countries as well as those in developing ones. Traveler's diarrhea affects approximately 40% of people traveling from industrialized countries to developing ones, and no pathogens are identified in many of those patients on their returning, suggesting that known enteropathogens escape detection or entirely new ones could be responsible. Very few reports of travel-related microsporidiosis have been described.

METHODS

Between January, 1996 and January, 1998, a total of 40 European travelers from the tropics with a clinical picture of protected diarrhea (three or more loose stools per day lasting for more than 3 weeks) were evaluated. Weber's trichrome modified by Kokoskin stain for microsporidial spores were performed in stool samples of every patient. Microsporidial DNA extraction and PCR amplification were attempted in every stool sample where microsporidial spores were observed.

RESULTS

Four cases of imported Enterocytozoon bieneusi were detected: one HIV-infected short term traveler, a pregnant long term traveler, and two immunocompetent short term travelers. Diarrhea was self-limited, and the spores cleared from the stools in all HIV-non infected travelers, but showed a chronic course in the HIV-infected one.

CONCLUSIONS

Available data is too limited to affirm that residence or travel in tropical countries increases the risk for microsporidial infection, but the cases presented here suggest that E. bieneusi could be a cause of self-limited diarrhea in immunocompetent travelers returning from the tropics or could chronically affect immunocompromised HIV-infected travelers.

Intestinal microsporidiosis occurring in two renal transplant recipients treated with mycophenolate mofetil

BACKGROUND

Intestinal microsporidiosis is a major cause of chronic diarrhea and malabsorption in patients with human immunodeficiency virus. Its occurrence in transplant recipients has exceptionally been reported to date.

METHODS

We report what we believe are the first two cases of intestinal microsporidiosis in renal transplant recipients. The patients were treated with mycophenolate mofetil.

RESULTS

The clinical presentation was chronic diarrhea with massive weight loss. Stool analysis revealed microsporidian spores, identified as Enterocytozoon bieneusi spores by polymerase chain reaction. The onset of this opportunistic infection in these two patients is believed to be secondary to an increase in immunosuppression after azathioprine replacement by mycophenolate mofetil. The withdrawal of mycophenolate mofetil led to clinical recovery.

CONCLUSION

The incidence of microsporidiosis will probably increase in transplant recipients treated with powerful immunosuppressants. Therefore, we recommend a systematic search for microsporidian spores in stool specimens in cases of unexplained diarrhea in these patients.

Cryptosporidia and microsporidia--waterborne diseases in the immunocompromised host

Cryptosporidia and microsporidia are emerging parasitic pathogens in immunocompetent and immunocompromised individuals. Cryptosporidium infects several wild and domestic animals that excrete oocysts into the environment and contaminated water represents the major source of infection for humans. Waterborne transmission of Cryptosporidium is a major risk for humans and appropriate measures have to be taken to protect immunocompetent and immunocompromised individuals to become infected. For microsporidia, the sources and ways of transmission are not well documented. Although several animal hosts have been identified recently, the relevant reservoirs of human microsporidia are still unknown. Also, the routes of spreading are unknown. Is microsporidiosis a zoonotic disease that will be transmitted through close contact with infected animals or is contaminated surface water responsible for transmission and represents a relevant reservoir? This review is designed to give information on these two emerging intestinal parasites in a format that will be useful to clinical microbiologists, physicians interested in infectious diseases, and public health personnel.

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.

Intestinal parasitic infections

Our understanding of the biology of several intestinal parasites has progressed considerably in the past year, especially in the area of molecular biology. Information from molecular and genetic analyses has been used increasingly to improve understanding of pathogenesis, to apply improved diagnostic methods, and to seek new vaccination strategies. There were fewer relevant clinical studies than in previous years, but some are notable. Control of helminth infections by mass chemotherapy in school age children appears an achievable goal in many communities. Vaccine trials against some protozoan infections continue to show promise in animal models.

Persistent damage to Enterocytozoon bieneusi, with persistent symptomatic relief, after combined furazolidone and albendazole in AIDS patients

AIM

To investigate morphological changes in Enterocytozoon bieneusi and the duration of symptomatic relief after combination treatment with furazolidone and albendazole in AIDS patients.

METHODS

Four severely immunocompromised AIDS patients with symptomatic E bieneusi infection of the gut received an 18 day course of combined furazolidone and albendazole (500 + 800 mg daily). All patients were monitored for parasite shedding in stool by light microscopy at the end of treatment and monthly during follow up. At the end of treatment, duodenal biopsy specimens obtained from three patients were studied by transmission electron microscopy by two pathologists blind to the patients' treatment or clinical outcome. Duodenal biopsy specimens obtained from one of the patients two months after completion of treatment were also studied electronmicroscopically.

RESULTS

All patients had long lasting symptomatic relief, with a major decrease--or transient absence--of spore shedding in stools from completion of treatment. After treatment, changes in faecal spores were persistently found by light microscopy in all cases, and there was evidence of both a substantial decrease in the parasite load and ultrastructural damage in the parasite in all biopsy specimens. The treatment was well tolerated, and no patient had clinical or parasitological relapse during follow up (up to 15 months).

CONCLUSIONS

The long lasting symptomatic relief observed in all four treated patients correlated with the persistent decrease in parasite load both in tissue and in stool, and with the morphological changes observed in the life cycle of the protozoan. These data suggest that combined treatment with furazolidone and albendazole is active against E bieneusi and may result in lasting remission even in severely immunocompromised patients.

Determination of types of Enterocytozoon bieneusi strains isolated from patients with intestinal microsporidiosis

To determine the types of Enterocytozoon bieneusi strains associated with intestinal microsporidiosis, we developed a rapid and efficient approach for typing parasites obtained from stool specimens by PCR-restriction fragment length polymorphism (PCR-RFLP). Typing was based on DNA polymorphism of the ribosomal DNA internal transcribed spacer (ITS) region of E. bieneusi. RFLPs generated with two restriction enzymes (NlaIII and Fnu4HI) in PCR-amplified ITS products were used to classify strains into different lineages. This approach was successfully used to differentiate 78 strains that had been obtained from the stools of 65 patients with intestinal microsporidiosis. Among the 78 strains, we found four genetically unrelated lineages, showing the genetic diversity of E. bieneusi. Type I strains of E. bieneusi were found in a majority of the samples, accounting for 51 (78%) of the 65 microsporidiosis cases. In contrast, type II, III, and IV strains were found in only 8 (12%), 3 (5%), and 3 (5%) cases, respectively. All strains of E. bieneusi we have tested so far fall into one of four different lineages, and this study shows that human intestinal microsporidiosis is most often associated with type I strains. PCR-RFLP analysis of the ITS region of E. bieneusi should be useful for epidemiological studies.

Potential efficacy of fumagillin in intestinal microsporidiosis due to Enterocytozoon bieneusi in patients with HIV infection: results of a drug screening study. The French Microsporidiosis Study Group

OBJECTIVE

Intestinal microsporidiosis due to Enterocytozoon bieneusi is a frequent cause of chronic diarrhoea in patients with HIV infection for which there is no available therapy. This study was designed to search for a drug with activity against this organism.

DESIGN

Prospective open-labelled Phase II multicentre study.

SETTING

University hospitals.

PATIENTS

Sixty HIV-infected men with intestinal E. bieneusi infection.

INTERVENTIONS

Ten drug regimens were consecutively tested orally for 3 weeks: albendazole plus metronidazole, sulphadiazine plus pyrimethamine, atovaquone, doxycycline plus nifuroxazide, itraconazole, flubendazole, chloroquine, paromomycin, sparfloxacin and fumagillin. Nine evaluable patients per regimen were required, but each patient could be enrolled up to three times in the study.

OUTCOME MEASURE

Efficacy was assessed primarily by the clearance of E. bieneusi from stools and intestinal biopsies. The safety of each regimen was also assessed.

RESULTS

Only purified fumagillin was able to clear E. bieneusi from stools as well as intestinal biopsies, whereas all other regimens failed to show antiparasitic efficacy. However, only four patients received fumagillin because of drug-induced thrombocytopenia. The four patients who received fumagillin remained free of E. bieneusi infection after a mean follow-up of 10 months.

CONCLUSION

Eradication of E. bieneusi from the intestinal tract of patients with HIV infection and persistent immunosuppression is an achievable goal. Our study allowed the identification of oral fumagillin as a potential treatment for intestinal microsporidiosis due to E. bieneusi.