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

Sexually transmitted infections and HIV in ophthalmology

The ocular and periocular manifestations of sexually transmitted infections are heterogeneous in etiology, manifestations, and complications. Etiologic agents include bacteria, viruses, parasites, and protozoa, which are most frequently transmitted via direct ocular contact with an active lesion or infected bodily fluid, autoinoculation, or dissemination from a distant site. Vertical transmission most commonly occurs perinatally during vaginal delivery. The complications of ophthalmia neonatorum can be severe, with the potential for permanent blindness or life-threatening systemic involvement if untreated. Clinical features, diagnostic modalities, and therapeutic regimens vary based on etiology and are summarized in this review. Prompt diagnosis is imperative, given the severe sequelae that may result from ocular involvement in these infections, including permanent vision loss. A multidisciplinary approach, involving both ophthalmology and dermatology, to diagnosis and management is essential to mitigate the risk of morbidity associated with sexually transmitted infections resulting in eye disease.

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.

Efficacy of fumagillin bicyclohexylamine on experimental corneal neovascularization in rat model

PURPOSE

Fumagillin has been previously used to treat corneal microsporidial keratitis and also identified as an angiogenesis inhibitor. This study aimed to evaluate efficacy of fumagillin bicyclohexylamine on the rat model of corneal neovascularization induced by silver nitrate cauterization.

METHODS

Twenty-four Albino Wistar rats (n = 24) were divided into three groups. Following silver nitrate-induced corneal injury, eyes in Group 1 received one drop of 5 mg/mL topical fumagillin bicyclohexylamine four times daily for 10 days. Group 2 received subconjunctival injection of 0.1 mL fumagillin bicyclohexylamine (2.5 mg/mL) on day 1 and day 5. Group 3 received artificial tears and lubricants four times daily for 10 days as control. On day 10, animals were sacrificed. Corneal specimens were obtained and prepared to assess vascular endothelial growth factor (VEGF-C) levels and corneal angiogenic microvessel density.

RESULTS

There was no significant difference in VEGF-C levels between the groups (P = 0.994). Assessment of angiogenic microvessel density for peripheral corneal zone also did not reveal significant difference between the groups (P = 0.113). However, mean vascular density in Group 1 and Group 2 was significantly higher for both midperipheral and central corneal zones in comparison with Group 3 (P = 0.003, P = 0.015).

CONCLUSIONS

Previously proved to be effective for treatment of microsporidial keratitis in humans, topical and subconjunctival concentration or dosing of fumagillin bicyclohexylamine failed to reduce corneal neovascularization induced by silver nitrate in this study. Further studies comparing different concentrations and dosing may detect inhibitory effects of fumagillin on corneal neovascularization without inducing toxicity.

Therapeutic targets for the treatment of microsporidiosis in humans

INTRODUCTION

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

Ophthalmic parasitosis: a review article

Ocular parasitosis in human is more prevalent in geographical areas where environmental factors and poor sanitary conditions favor the parasitism between man and animals. Lesions in the eye can be due to damage directly caused by the infectious pathogen, indirect pathology caused by toxic products, or the immune response incited by infections or ectopic parasitism. The epidemiology of parasitic ocular diseases reflects the habitat of the causative parasites as well as the habits and health status of the patient. An ocular examination may provide clues to the underlying disease/infection, and an awareness of the possibilities of travel-related pathology may shed light on an ocular presentation. This paper is a comprehensive review of the parasitic diseases of the eye. The majority of the clinically important species of parasites involved in eye infection are reviewed in this paper. Parasites are discussed by the disease or infection they cause.

Clinical trial of 0.02% polyhexamethylene biguanide versus placebo in the treatment of microsporidial keratoconjunctivitis

PURPOSE

To evaluate the efficacy of 0.02% polyhexamethylene biguanide (PHMB) in the treatment of keratoconjunctivitis caused by microsporidia.

DESIGN

Prospective, double-masked, randomized, placebo-controlled clinical trial.

METHODS

One hundred forty-five patients in a single-center, institutional setting were recruited. Patients with superficial keratoconjunctivitis and corneal scrapings with positive results for microsporidial spores were included. Patients with any known allergy to PHMB, and clinically suspected bacterial, viral, or fungal infection were excluded from the study. One hundred forty-five patients were treated at 4-hour intervals with either topical 0.02% PHMB (n = 72) or placebo (n = 73). The patients were followed-up on day 3 +/- 1, day 7 +/- 1, and weekly thereafter, until complete resolution of the corneal lesions. Patients with deterioration of clinical symptoms and signs were removed from the study and were treated with PHMB. Main outcome measures included resolution time, cure time, and final visual outcome.

RESULTS

Resolution time was defined as the amount of time until disappearance of corneal epithelial infiltrates. Cure time was defined as the interval until absence of conjunctival congestion, corneal epithelial lesion, and superficial punctate keratitis. Baseline characteristics showed no relevant difference between the groups. The mean resolution time was 4.9 +/- 2.2 days and 4.6 +/- 2.3 days in the PHMB and placebo groups, respectively (P = .49). The mean time for cure was 13.5 +/- 6.6 days and 9.4 +/- 5.1 days in PHMB and placebo groups, respectively (P = .004). There was no significant difference in the final visual outcome between the groups (P = .10). No serious adverse effects were noted.

CONCLUSIONS

Treatment of microsporidial keratoconjunctivitis with PHMB does not offer any significant advantage over placebo, suggesting self-limiting nature of the disease.

Testing intra-hemocelic injection of antimicrobials against Encephalitozoon sp. (Microsporidia) in an insect host

Encephalitozoon spp. are the primary microsporidial pathogens of humans and domesticated animals. In this experiment, we test the efficacy of four commercial antimicrobials against an Encephalitozoon sp. in an insect host by intra-hemocelic injection. All four antimicrobials, viz., thiabendazole, quinine, albendazole, and fumagillin, significantly reduced but did not eliminate microsporidia spore counts in the grasshopper host. Among these four drugs, thiabendazole was most effective in reducing the microsporidia spore level up to 90%, followed by quinine (70%), albendazole (62%), and fumagillin (59%). No control or quinine-treated animals died, whereas 45% of albendazole animals died. Despite the high mortality induced by albendazole, this drug significantly reduced spore counts, a result not seen in previous per os trials. Among the treatment groups, grasshoppers injected with thiabendazole lost a significant mass. Our study suggests that quinine and related alkaloids should be further examined for antimicrosporidial activity.

Anterior segment manifestations of human immunodeficiency virus/acquired immune deficiency syndrome

Ocular complications are known to occur as a result of human immunodeficiency virus (HIV) disease. They can be severe leading to ocular morbidity and visual handicap. Cytomegalovirus (CMV) retinitis is the commonest ocular opportunistic infection seen in acquired immune deficiency syndrome (AIDS). Though posterior segment lesions can be more vision-threatening, there are varied anterior segment manifestations which can also lead to ocular morbidity and more so can affect the quality of life of a HIV-positive person. Effective antiretroviral therapy and improved prophylaxis and treatment of opportunistic infections have led to an increase in the survival of an individual afflicted with AIDS. This in turn has led to an increase in the prevalence of anterior segment and adnexal disorders. Common lesions include relatively benign conditions such as blepharitis and dry eye, to infections such as herpes zoster ophthalmicus and molluscum contagiosum and malignancies such as squamous cell carcinoma and Kaposi′s sarcoma. With the advent of highly active antiretroviral therapy, a new phenomenon known as immune recovery uveitis which presents with increased inflammation, has been noted to be on the rise. Several drugs used in the management of AIDS such as nevirapine or indinavir can themselves lead to severe inflammation in the anterior segment and adnexa of the eye. This article is a comprehensive update of the important anterior segment and adnexal manifestations in HIV-positive patients with special reference to their prevalence in the Indian population.

Effect of four antimicrobials against an Encephalitozoon sp. (Microsporidia) in a grasshopper host

Encephalitozoon spp. are the primary microsporidial pathogens of humans and domesticated animals. In this experiment, we test the efficacy of 4 commercial antimicrobials against an Encephalitozoon sp. infecting a grasshopper (Romalea microptera) host. Oral treatment with fumagillin or thiabendazole significantly reduced pathogen spore counts (93% and 88% respectively), whereas spore counts of grasshoppers fed quinine produced a non-significant 53% reduction in spores, and those fed streptomycin a non-significant 29% increase in spores, compared to the control. We observed a moderate dose-response effect for thiabendazole, whereby spore count decreased as drug consumption increased. No thiabendazole-treated animals died, whereas 27% of streptomycin-treated animals died, suggesting that thiabendazole was not toxic at the doses administered. The deaths among streptomycin-treated animals may have been caused by drug toxicity, parasite burden, or both. Although fumagillin and thiabendazole significantly reduced spore counts, in no individual was the pathogen totally eliminated. Our data confirm that microsporidia are difficult to control and that fumagillin and thiabendazole are partially effective antimicrobials against this group. Our study suggests that quinine and related alkaloids should be further examined for antimicrosporidial activity, and streptomycin should be examined as a possible enhancer of microsporidiosis.

Anterior Segment and External Ocular Disorders Associated with Human Immunodeficiency Virus Disease

The eye is a common site for complications of human immunodeficiency virus (HIV) infection. Although cytomegalovirus retinitis remains the most prevalent of the blinding ocular disorders that can occur in individuals with the acquired immunodeficiency syndrome (AIDS), several important HIV-associated disorders may involve the anterior segment, ocular surface, and adnexae. Some of these entities, such as Kaposi sarcoma, were well described, but uncommon, before the HIV epidemic. Others, like microsporidial keratoconjunctivitis, have presentations that differ between affected individuals with HIV disease and those from the general population who are immunocompetent. The treatment of many of these diseases is challenging because of host immunodeficiency. Survival after the diagnosis of AIDS has increased among individuals with HIV disease because of more effective antiretroviral therapies and improved prophylaxis against, and treatment of, opportunistic infections. This longer survival may lead to an increased prevalence of anterior segment and external ocular disorders. In addition, the evaluation and management of disorders such as blepharitis and dry eye, which were previously overshadowed by more severe, blinding disorders, may demand increased attention, as the general health of this population improves. Not all individuals infected with HIV receive potent antiretroviral therapy, however, because of socioeconomic or other factors, and others will be intolerant of these drugs or experience drug failure. Ophthalmologists must, therefore, still be aware of the ocular findings that develop in the setting of severe immunosuppression. This article reviews the spectrum of HIV-associated anterior segment and external ocular disorders, with recommendations for their evaluation and management.

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).

Ultrastructural examination of two cases of stromal microsporidial keratitis

Two cases with chronic stromal keratitis are described in immunocompetent hosts where the diagnosis was originally thought to be herpetic or adenoviral disease. Light microscopy and ultrastructural examination of corneal tissue by electron microscopy were performed following penetrating keratoplasty (case 1) and corneal biopsy (case 2). Specimens from both cases were analysed for viral identification by PCR. Two different species of Microsporidia were identified. Case 1 represents the fourth reported case of corneal stromal Vittaforma corneae where the spores measured 3.3 x 1.4 microm, arranged in characteristic linear groups of about four to eight. Each spore contained a diplokaryotic nucleus and a single row of ten polar tube coils. By contrast, case 2 is the first reported case of stromal keratitis caused by Trachipleistophora hominis. In this case, spores measured 4 x 2.4 microm, located typically within packets. In this species, the polar tube was arranged as a single row of about 10-13 profiles. Viral DNA could not be amplified by PCR. In conclusion, microsporidial stromal keratitis should be considered in culture-negative cases refractory to medical therapy. As microbiological culture techniques are unsuccessful, diagnosis may only be established following histopathological and ultrastructural examination of corneal tissue.

Microsporidial keratoconjunctivitis in healthy individuals: a case series

PURPOSE

To present a series of 6 cases of microsporidial keratoconjunctivitis in healthy, nonimmunocompromised individuals.

DESIGN

Retrospective, noncomparative case series.

PARTICIPANTS

Six individuals with unilateral keratoconjunctivitis.

METHODS

Cornea epithelial scrapings were taken and evaluated by modified trichome staining. Blood was taken for human immunodeficiency virus (HIV) enzyme-linked immunosorbent assay in all cases and for CD4 and CD8 T-lymphocyte counts in 5 cases.

MAIN OUTCOME MEASURES

The individuals were evaluated based on symptoms, visual acuity, slit-lamp biomicroscopy, and pathologic examination of the corneal scrapings.

RESULTS

All cases occurred in men whose ages ranged from 16 to 37 years. Initial symptoms included unilateral pain and redness. All experienced subsequent worsening of symptoms and blurring of vision after using topical steroids prescribed by general practitioners. Slit-lamp biomicroscopy revealed coarse, multifocal, punctate epithelial keratitis in all 6 cases, anterior stromal infiltrates in 2 cases, with accompanying conjunctivitis in all cases. Modified trichrome staining of corneal epithelial scrapes revealed pinkish to red spores characteristic of microsporidia in all cases. Results of an HIV enzyme-linked immunosorbent assay were negative in all cases, and CD4 and CD8 T-lymphocyte counts and ratios were normal in all 5 tested cases. On diagnosis, topical steroid therapy was stopped in all cases. Treatment with topical Fumidil B (bicyclohexylammonium fumagillin; Leiter's Park Ave Pharmacy, San Jose, CA) together with oral albendazole was given in 3 cases, oral albendazole alone in a single case, and broad-spectrum antibiotic treatment with topical norfloxacin or chloramphenicol in two cases. Two cases had keratic precipitates with mild cellular activity in the anterior chamber and one such case was restarted subsequently on topical steroids. All six cases showed resolution of epithelial keratitis but with residual visually inconsequential subepithelial scars by the end of 1 month of treatment.

CONCLUSIONS

Microsporidial keratoconjunctivitis can occur more commonly than expected in healthy, nonimmunocompromised individuals. Topical steroids seem to contribute to the persistence of this infection and may be a predisposing factor in these cases by creating a localized immunocompromised state. The clinical course is variable and may be self-limiting with cessation of topical steroid use.

Bilateral microsporidial keratoconjunctivitis in an immunocompetent non-contact lens wearer

PURPOSE

To describe an immunocompetent male with bilateral microsporidial keratoconjunctivitis who responded to treatment with albendazole, propamidine, and fumagillin.

METHODS

Corneal and conjunctival epithelial scrapings from a man with bilateral keratoconjunctivitis previously treated with topical corticosteroids were evaluated by Gram stain and by fluorescence microscopy.

RESULTS

Gram stain and fluorescence microscopy of corneal epithelial scraping revealed organisms characteristic of microsporidia. Results of human immunodeficiency virus antibody testing were reported as nonreactive. Symptoms of ocular discomfort and clinical signs of keratoconjunctivitis resolved after five weeks of treatment that included systemic albendazole and topical propamidine isethionate 0.1% and fumagillin bicyclohexylammonium salt. A follow-up conjunctival scraping failed to detect any residual organisms 2 weeks after cessation of all treatment.

CONCLUSION

Microsporidial ocular infection occurred in an immunocompetent non-contact lens wearer. Microsporidial keratoconjunctivitis should be considered in any individual with atypical multifocal diffuse epithelial keratitis, regardless of immune status or recent history of contact lens wear.

Disseminated infection with encephalitozoon intestinalis in AIDS patients: report of 2 cases

Microsporidiosis must be regarded as a late opportunistic infection when HIV is advanced. In this article we describe 2 cases of disseminated infection with Encephalitozoon intestinalis. The first case had a local intestinal infection for > 1 y before it disseminated and microsporidia were found intracellularly in sputum. In the second case, spores were initially found in conjunctival cells, sinus lavage, sputum and urine. This patient had clinical symptoms and radiological findings from the central nervous system. Signs of cerebral lymphoma developed after treatment of the opportunistic microsporidial infection.

In vitro cultivation of microsporidia of clinical importance

Although attempts to develop methods for the in vitro cultivation of microsporidia began as early as 1937, the interest in the culture of these organisms was confined mostly to microsporidia that infect insects. The successful cultivation in 1969 of Encephalitozoon cuniculi, a microsporidium of mammalian origin, and the subsequent identification of these organisms as agents of human disease heightened interest in the cultivation of microsporidia. I describe the methodology as well as the cell lines, the culture media, and culture conditions used in the in vitro culture of microsporidia such as Brachiola (Nosema) algerae, Encephalitozoon cuniculi, E. hellem, E. intestinalis, Enterocytozoon bieneusi, Trachipleistophora hominis, and Vittaforma corneae that cause human disease.

Microsporidial keratoconjunctivitis in a healthy contact lens wearer without human immunodeficiency virus infection

PURPOSE

To present a rare case of microsporidial keratoconjunctivitis in an otherwise healthy contact lens wearer without human immunodeficiency virus infection who responded to treatment with systemic albendazole and topical fumagillin.

DESIGN

Interventional case report.

METHOD

A cornea epithelial scraping from a man with unilateral keratoconjunctivitis previously treated with topical steroids was evaluated by modified trichome staining.

MAIN OUTCOME MEASURES

The patient was evaluated for his symptoms, visual acuity, clinical observations, and pathologic examination of corneal scrapes.

RESULTS

Modified trichome staining of an epithelial corneal scraping revealed pinkish to red organisms characteristic of microsporidia. Results of a human immunodeficiency virus (HIV) enzyme-linked immunosorbent assay test were negative. The symptoms of ocular discomfort and clinical signs of keratoconjunctivitis resolved after 2 months of treatment with albendazole and topical fumagillin.

CONCLUSIONS

Ocular infection with microsporidia, although classically occurring in patients with HIV infection, may occur rarely in healthy individuals, especially if previously treated with systemic immune suppression or topical steroids. Microsporidial keratoconjunctivitis should be considered in the differential diagnosis of a contact lens wearer with atypical multifocal diffuse epithelial keratitis.

Fungal and parasitic infections of the eye

The unique structure of the human eye as well as exposure of the eye directly to the environment renders it vulnerable to a number of uncommon infectious diseases caused by fungi and parasites. Host defenses directed against these microorganisms, once anatomical barriers are breached, are often insufficient to prevent loss of vision. Therefore, the timely identification and treatment of the involved microorganisms are paramount. The anatomy of the eye and its surrounding structures is presented with an emphasis upon the association of the anatomy with specific infection of fungi and parasites. For example, filamentous fungal infections of the eye are usually due to penetrating trauma by objects contaminated by vegetable matter of the cornea or globe or, by extension, of infection from adjacent paranasal sinuses. Fungal endophthalmitis and chorioretinitis, on the other hand, are usually the result of antecedent fungemia seeding the ocular tissue. Candida spp. are the most common cause of endogenous endophthalmitis, although initial infection with the dimorphic fungi may lead to infection and scarring of the chorioretina. Contact lens wear is associated with keratitis caused by yeasts, filamentous fungi, and Acanthamoebae spp. Most parasitic infections of the eye, however, arise following bloodborne carriage of the microorganism to the eye or adjacent structures.

Fungal and parasitic infections of the eye

The unique structure of the human eye as well as exposure of the eye directly to the environment renders it vulnerable to a number of uncommon infectious diseases caused by fungi and parasites. Host defenses directed against these microorganisms, once anatomical barriers are breached, are often insufficient to prevent loss of vision. Therefore, the timely identification and treatment of the involved microorganisms are paramount. The anatomy of the eye and its surrounding structures is presented with an emphasis upon the association of the anatomy with specific infection of fungi and parasites. For example, filamentous fungal infections of the eye are usually due to penetrating trauma by objects contaminated by vegetable matter of the cornea or globe or, by extension, of infection from adjacent paranasal sinuses. Fungal endophthalmitis and chorioretinitis, on the other hand, are usually the result of antecedent fungemia seeding the ocular tissue. Candida spp. are the most common cause of endogenous endophthalmitis, although initial infection with the dimorphic fungi may lead to infection and scarring of the chorioretina. Contact lens wear is associated with keratitis caused by yeasts, filamentous fungi, and Acanthamoebae spp. Most parasitic infections of the eye, however, arise following bloodborne carriage of the microorganism to the eye or adjacent structures.

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.

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.

Effects of albendazole, fumagillin, and TNP-470 on microsporidial replication in vitro

Presently, the two most commonly used drugs for treating microsporidiosis in persons with AIDS are albendazole and fumagillin. Albendazole is effective for treating disseminated infections due to Encephalitozoon spp. but is variably effective against Enterocytozoon bieneusi infections. Fumagillin is highly effective when used topically to treat ocular infections with Encephalitozoon hellem or Encephalitozoon intestinalis but is too toxic for systemic use. In this study, the fumagillin analog TNP-470 was assayed for antimicrosporidial activity in vitro. The MICs of TNP-470 at which 50% of isolates were killed (MIC50s) were 0.35 +/- 0.21 and 0.38 +/- 0.11 ng/ml for E. intestinalis and Vittaforma corneae, respectively, and were similar to the MIC50s of fumagillin for these organisms, which were 0.515 +/- 0.002 and 0.81 +/- 0.014 ng/ml, respectively. The MIC50 of albendazole for E. intestinalis was 8.0 +/- 4.23 ng/ml, significantly less (P < 0.01) than its MIC50 for V. corneae, which was 55.0 +/- 7.07 ng/ml. TNP-470 inhibited replication of E. intestinalis in RK-13 cells if it was given at the same time as infection or if treatment was initiated 7 days later. In addition, treatment of the infected cultures with TNP-470 at a dose of 10 ng/ml for 2 weeks, followed by discontinuation of the drug treatment, resulted in no significant increase in E. intestinalis shedding during the following 3 weeks in culture. Because TNP-470 acts against both E. intestinalis and V. corneae, and because TNP-470 was found by others to be less toxic in vivo, TNP-470 may be a promising new drug for the treatment of microsporidiosis.