Ultrastructural examination of two cases of stromal microsporidial keratitis

Encephalitis and myositis caused by Trachipleistophora hominis diagnosed by metagenomic next-generation sequencing-a case report

Background

Myositis is the main manifestation of Trachipleistophora hominis (T. hominis) infection and other microsporidians infection in immunocompromised patients. Clinical differential diagnosis of different microsporidians can be challenging, as the standard technique to distinguish various microsporidia species, transmission electron microscopy (TEM), is time-consuming and relies on equipment and experienced staffs who can perform the test and interpret the results.

Case presentation

We report a 37-year-old Chinese man with acquired immune deficiency syndrome (AIDS) developed headache and muscle pain in the extremities. Tramadol was used to relieve his pain. Infectious lesions in his brain were detected by cerebral magnetic resonance imaging (MRI). Oval-shaped pathogens was observed by biopsy of right gastrocnemius. Finally, T. hominis was identified by metagenomic next-generation sequencing (mNGS) in the gastrocnemius tissue and cerebrospinal fluid. After a 12-week course of antifungal treatment and antiretroviral therapy, the patient recovered from the encephalitis and myositis caused by T. hominis.

Conclusion

This report described the diagnosis and treatment of the first case of encephalitis caused by T. hominis. And mNGS is recommended for the rapid diagnosis of uncommon pathogens.

Trachipleistophora hominis: molecular characterization of a rare pathogen causing microsporidial stromal keratitis

The authors report the clinical and microbiological findings of a unique case of stromal keratitis caused by a rare microsporidium, Trachipleistophora hominis. This case of stromal keratitis was in a 49-year-old male with a history of COVID-19 infection and diabetes mellitus. Corneal scraping specimens revealed numerous microsporidia spores upon microscopic examination. PCR of the corneal button revealed the presence of T. hominis infection, which could be controlled by penetrating keratoplasty surgery. The graft was clear with no recurrence of infection until the last follow-up 6 weeks postsurgery. This is the first case of human stromal keratitis caused by this organism in a post-COVID infection, confirmed by molecular diagnosis.

[Ophthalmic findings caused by Encephalitozoon cuniculi (strain III) in a dog]

A 2-year-old female mixed-breed canine patient from Namibia presented originally with chronic uveitis. A serum antibody titer and a PCR test performed on the aqueous humor were positive for encephalitozoon cuniculi. The left eye showed an immature anterior focal cortical cataract in the periphery with suspected lens capsule rupture and signs of chronic uveitis. An incipient anterior focal cortical cataract was also perceivable in the patient's right eye. Despite local treatment as well as systemic administration of carprofen, prednisolone, and fenbendazol recurrent uveitis occurred. The patient then underwent bilateral extracapsular lensextraction via phacoemulsification. A PCR test of the lens material was positive for encephalitozoon cuniculi strain III. Recurring uveitis and secondary glaucoma 10 months post-op resulted in permanent blindness of the left eye. The patient then continued to receive local anti-inflammatory treatment. The last recheck examination of both eyes, 31 month post-op, revealed no signs of uveitis. This is the first case reported of a cataract in a canine patient caused by encephalitozoon cuniculi strain III.

Microsporidia, a Highly Adaptive Organism and Its Host Expansion to Humans

Emerging infectious disease has become the center of attention since the outbreak of COVID-19. For the coronavirus, bats are suspected to be the origin of the pandemic. Consequently, the spotlight has fallen on zoonotic diseases, and the focus now expands to organisms other than viruses. Microsporidia is a single-cell organism that can infect a wide range of hosts such as insects, mammals, and humans. Its pathogenicity differs among species, and host immunological status plays an important role in infectivity and disease severity. Disseminated disease from microsporidiosis can be fatal, especially among patients with a defective immune system. Recently, there were two Trachipleistophora hominis, a microsporidia species which can survive in insects, case reports in Thailand, one patient had disseminated microsporidiosis. This review gathered data of disseminated microsporidiosis and T. hominis infections in humans covering the biological and clinical aspects. There was a total of 22 cases of disseminated microsporidiosis reports worldwide. Ten microsporidia species were identified. Maximum likelihood tree results showed some possible correlations with zoonotic transmissions. For T. hominis, there are currently eight case reports in humans, seven of which had Human Immunodeficiency Virus (HIV) infection. It is observed that risks are higher for the immunocompromised to acquire such infections, however, future studies should look into the entire life cycle, to identify the route of transmission and establish preventive measures, especially among the high-risk groups.

A case of stromal microsporidiosis: medical strategies employed for successful resolution

We describe the diagnosis and successful management of a case of stromal microsporidiosis, an important emerging ocular disease. Stromal microsporidiosis is recalcitrant and very often requires therapeutic keratoplasty for effective eradication. We successfully managed a steroid-treated case diagnosed only after 9 months, with a combination of polyhexamethyl biguanide 0.04%, chlorhexidine 0.04% and fluconazole 0.3% eye drops supplemented with tablet albendazole. However, complete resolution was achieved only after epithelial debridement. Toxicity due to the drugs was not noted. Diagnostic delays, steroid use and inappropriate therapy are commonly observed in stromal microsporidiosis. In spite of these potential disadvantages, our case responded well with complete eradication of the infection. The disease being fairly indolent and slowly progressive, medical therapy should be continued, in the absence of progression or other complications. Epithelial debridement may facilitate healing.

Microsporidial Stromal Keratitis: Epidemiological Features, Slit-Lamp Biomicroscopic Characteristics, and Therapy

PURPOSE

Microsporidial stromal keratitis is a rare form of infectious keratitis, with only 7 cases reported in the United States to date. This study was performed to evaluate risk factors, clinical features, and response to therapy.

METHODS

A retrospective review of the medical records of all patients diagnosed with microsporidial stromal keratitis seen in the practices of the authors between 1999 and 2020 was performed. Diagnosis was determined by cytology or histopathology in corneal specimens. Risk factors, presence or absence of distinctive clinical features, and response to medical and surgical therapies were recorded.

RESULTS

Nine patients-7M:2F, aged 7 to 99 years-with microsporidial stromal keratitis were identified. Exposures to recreational water and hymenopteran insect bites, both epidemiologically linked risk factors for systemic microsporidial infection, were identified in our patients. Presence of stromal edema with features of disciform keratitis and a distinctive granular keratitis were observed in 6 of 9 and 5 of 9 patients, respectively. Poor response to medical therapy was noted. Penetrating keratoplasty was effective in curing the infection. Final visual acuity was 20/40 or better in 6 of 9 patients.

CONCLUSIONS

In patients with slowly progressive keratitis, history of exposure to recreational water or hymenopteran insects should be sought. In patients with corneal edema consistent with disciform keratitis, with evolution to a granular keratitis, microsporidia should be considered in the differential diagnosis. In cases of established microsporidial stromal keratitis, penetrating keratoplasty should be considered if prompt response to medical therapy is not noted.

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.

Acute stromal keratitis in clinics - are we missing microsporidia?

Purpose: To report 3 cases of microsporidial stromal keratitis presenting as a diagnostic dilemma to a tertiary eye care center in north India.

Methods: Three eyes of 3 patients underwent therapeutic keratoplasty for microsporidial stromal keratitis. A decision for early surgery was taken as the patients were not responding to conventional medical management and were worsening clinically. The diagnosis of microsporidia was made by corneal scraping and confirmed on histopathological evaluation of the corneal button.

Results: Out of the 3 patients, one maintained a clear graft, one had a recurrence and one had graft rejection, 6 months postoperatively. The patients were not started on steroids in the postoperative period and were given topical antibiotics and polyhexamethylene biguanide (PHMD). Oral Albendazole 400 mg was also given twice a day for a month.

Conclusion: Many questions remained unanswered about the management protocol of stromal keratitis caused by microsporidia. The role of topical steroids, antifungal agents, oral Albendazole needs to be discussed. Clinicians should be aware of recurrences which may mimic as rejections. There needs to be more awareness regarding microsporidia as a cause of acute stromal keratitis, so that its not overlooked or underdiagnosed.

Microsporidial keratopathy in two dogs

A microsporidial keratopathy is described in two dogs. Both dogs presented with a unilateral stromal keratopathy characterized by multifocal coalescing opacities, and the diagnosis was made on histopathologic examination of keratectomy specimens. Transmission electron microscopy (TEM) on formalin-fixed, paraffin-embedded corneal tissue was performed in one dog, and the morphologic features were consistent with Nosema species infection. Both dogs were initially diagnosed and treated by superficial keratectomy. One dog received additional antifungal medication and underwent a penetrating keratoplasty following local recurrence two years later. No other systemic lesions attributable to the microsporidial infection were identified clinically. The clinical and diagnostic pathology findings, treatment, and follow-up are discussed.

Demographic and clinical profile of microspodial keratitis in North India: an underreported entity

Ocular microsporidiosis was first described in immunocompromised subjects but recent reports have also shown cases in immunocompetent hosts. The database of existing clinical studies is very limited. The aim of present study was to analyse demographic profile, clinical features, microbiological profile, treatment and outcome of ocular microsporidiosis in northern India. The present study was carried out in the Department of Medical Parasitology, Advanced Eye Center, Postgraduate Institute of Medical Education and Research, and Bharat Vikas Parishad Charitable trust, Chandigarh. A total of 250 patients during year 2013-17 and suspected of microsporidial keratitis (either clinically or after exclusion of bacterial, viral or fungal agents). Corneal scraping were taken and subjected for various staining methods and PCR. 8 patients of microsporidial keratitis were confirmed, based on positivity by at least any two of the above mentioned techniques. None of the patients had history of contact lens wear or exposure to swimming pool. All these patients were systemically healthy and HIV serology was negative except one had history of diabetes mellitus. This study is a reminder to clinicians that when multifocal diffuse epithelial keratitis and culture-negative keratoconjunctivitis not responding to medical therapy, regardless of immune status are found in patients with symptoms suggesting an infectious keratitis, microsporidial keratoconjunctivitis should be included in the differential diagnosis.

Microsporidial Stromal Keratitis: Clinical Features, Unique Diagnostic Criteria, and Treatment Outcomes in a Large Case Series

PURPOSE

To describe the history, clinical features, and outcomes of a large case series of microsporidial stromal keratitis with emphasis on probable predictors of the etiology in this rare and unspecified form of keratitis.

METHODS

Retrospective analysis of cases seen between January, 2002, and December, 2013, diagnosed at LV Prasad Eye Institute as having microsporidial stromal keratitis based on clinical, microbiology, and histopathology examination. Outcomes of medical and surgical management with visual recovery were documented.

RESULTS

There were 34 cases of microsporidial stromal keratitis with a mean age of 43.3 years (range 2-77 years) and male preponderance. The duration of symptoms was chronic in most cases (mean duration of 288 days). Nearly half of the cases had a history of trauma, in the age group of 20 to 50 years. The most common clinical misdiagnosis was herpes simplex virus keratitis (26.5%) followed by fungal keratitis (17.6%). This could be attributed to the nonspecific clinical picture of diffuse multifocal stromal lesions in 82.4% of cases. The organisms were detected in microbiological evaluation of corneal scrapings in 47% cases, and histopathological detection of the organisms showed a positivity rate of 92.3%. Surgical management was necessary in the majority of the cases (73.5% of patients).

CONCLUSIONS

The typical history of trauma with a smoldering, diffuse form of keratitis refractory to conventional medical therapy, responding to surgical removal for recovery is clearly demonstrated as a recurring feature in the majority of the cases. Patients presenting with this characteristic clinical picture should be suspected to harbor this rare pathogen, and early surgical interventions should be considered.

Microsporidia infection of the cornea--a unique and challenging disease

Microsporidia are a diverse group of obligate, intracellular, eukaryotic, spore-forming parasites. Traditionally, these were considered as protozoans but recently have been reclassified as fungi. Microsporidia behave as opportunistic pathogens causing systemic infections. In the eye, Microsporidia cause keratoconjunctivitis, corneal stromal keratitis, scleritis, and endophthalmitis. This review shares our experiences with anterior segment infections caused by this pathogen. Keratoconjunctivitis is a common form of ocular infection caused by the parasite. Although early reports described it as occurring only in immunosuppressed individuals, it can also occur in immunocompetent individuals. The disease shows a seasonal pattern with a peak incidence during the rainy season. Although several drugs have been considered, our experience suggests that keratoconjunctivitis is a self-limiting disease. In contrast to keratoconjunctivitis, stromal keratitis is an ill-defined disease. We collected 30 cases and analyzed the various aspects of this disease. Stromal keratitis is characterized by a slowly progressive course. The corneal picture resembles herpes simplex virus stromal keratitis or fungal keratitis cases, and is characterized by deep stromal infiltrates with overlying and surrounding stromal edema and keratic precipitates. The diagnosis of Microsporidia infection is confirmed by a microscopic examination of smears from patients with ulcerative keratitis or by a histopathological examination of corneal tissues. Definitive genus identification requires the examination of specimens by electron microscopy or by molecular methods. In the absence of a definitive medical treatment, nearly all patients require surgical treatment. The confusion regarding Microsporidia is not only limited to their classification but also extends to various aspects of the corneal disease caused by them.

Treatment of microsporidial keratoconjunctivitis with repeated corneal swabbing

PURPOSE

To report the effect of repeated corneal swabbing in patients with microsporidial keratoconjunctivitis.

DESIGN

Retrospective noncomparative case series.

METHODS

Sixteen eyes of 14 healthy patients with microsporidial keratoconjunctivitis were diagnosed based on the detection of microsporidia in corneal scrapings using Gram stain, the modified Kinyoun acid-fast stain, or both. Polymerase chain reaction plus gene analysis of the microsporidian 16S ribosomal RNA had been performed in 10 patients who sought treatment between 2010 and 2011. Some of the lesions were scraped for procurement of specimens. The remaining lesions were wiped off gently by cotton swabs. Repeated swabbing was performed if infection persisted or new lesions were observed at follow-up. To prevent secondary bacterial infection, 0.3% norfloxacin or 0.25 % chloramphenicol were prescribed.

RESULTS

The mean age was 52.2 years. All patients had the characteristic disseminated, punctate, slightly elevated, white epithelial lesions. The denser white lesions could be removed easily after gentle swabbing, and most epithelium remained intact. The 10 cases with positive polymerase chain reaction results were all identified to be Vittaforma corneae. The mean number of corneal swabbing was 3.3, and the mean disease resolution time was 6.6 days. No patients had recurrence or loss of visual acuity at last follow-up.

CONCLUSIONS

Repeated swabbing effectively can eradicate corneal epithelial microsporidial lesions in approximately 1 week. It is easy to perform, less painful, and more acceptable for the patients.

Clinical spectrum of microsporidial keratoconjunctivitis

The purpose of this paper was to analyse the causes, pathogenesis, diagnostic modalities and treatment outcomes of microsporidial keratoconjunctivitis (MKC). Microsporidia are increasingly recognized as opportunistic infectious pathogens in immunocompromized patients causing keratoconjunctivitis. In the recent years, there has been a surge in reports of MKC in immunocompetent individuals presenting with stromal keratitis. A detailed literature search was done using Medline, OVID, Cochrane Library, UptoDate and Google Scholar databases with the terms microsporidia, keratitis, conjunctivitis, immunocompromized and immunocompetent. The articles were reviewed to determine the spectrum of clinical presentation, disease course, investigations, treatment modalities and outcome. Thirty-six publications were reviewed, and 151 cases of MKC were included for this review. The main presenting features included pain, redness, photophobia, epiphora and blurring of vision. Duration of the symptoms lasted between 4 days and 18 months. Light microscopy with modified trichrome stain was most commonly used to diagnose MKC. Resolution of symptoms was most commonly achieved with oral albendazole and/or topical fumidil B. Topical fluoroquinolones are also effective as a monotherapy as suggested by recent studies. Clinical outcome was good (visual acuity ≤ 6/12) for the patients who presented earlier (≤1 month) (75% of cases with documented final best-corrected visual acuity). MKC occurs more commonly in immunocompetent individuals than expected and can be diagnosed in earlier stages. From our review, we conclude that the patients, who were diagnosed early and treated, had complete resolution of symptoms with a better clinical outcome.

Microsporidial keratitis in patients with hot springs exposure

This retrospective study included 10 eyes of 9 patients diagnosed with microsporidial keratitis. All of them were known to contract this disease after taking baths in hot springs. The disease was diagnosed based on detecting microsporidia in corneal scrapings using Gram stain and the modified Kinyoun's acid-fast stain. The specimens from the last six patients were subjected to PCR and then sequencing. All of them revealed that the microorganism identified has a high similarity to Vittaforma corneae. Repeated debridement of the epithelial lesions successfully eradicated the microsporidial infection in all nine patients.

Analysis of the beta-tubulin gene from Vittaforma corneae suggests benzimidazole resistance

We amplified, cloned, and sequenced the beta-tubulin gene of Vittaforma corneae, a microsporidium causing human infections. The beta-tubulin gene sequence has a substitution at Glu(198) (with glutamine), which is one of six amino acids reported to be associated with benzimidazole sensitivity. Benzimidazoles were assayed for antimicrosporidial activity and showed poor parasite inhibition.

A case of bilateral microsporidial keratitis from Bangladesh – infection by an insect parasite from the genus Nosema

An HIV-negative patient from Bangladesh with bilateral keratitis was found to be infected with a microsporidian parasite belonging to the genus Nosema. Significantly, the patient had bathed in a rural pond 7 days prior to the development of ocular symptoms. Nosema parasites are common insect parasites and the source of this microsporidial infection was possibly from mosquito larvae developing in the pond in which the patient bathed. The reduced temperature of the human eye and its immune status may have allowed a poikilothermic insect parasite to establish infection in the cornea of a homeothermic human host. This case highlights the opportunistic potential of insect microsporidial parasites to infect immunocompetent humans as well as those who are immunodeficient.

Microsporidium Stromal Keratitis: In Vivo Confocal Findings

PURPOSE

To relate the clinical signs, histopathologic features, and in vivo confocal biomicroscopy findings of a case of stromal microsporidial keratitis and to describe the use of in vivo confocal microscopy to monitor treatment effect.

METHODS

An immunocompetent male patient presented with unilateral indolent stromal keratitis. Stromal microsporidiosis was confirmed after corneal biopsy. He underwent examination that used in vivo confocal microscopy (Heidelberg Retina Tomograph II and Rostock Cornea Module) before and after treatment with topical fumagillin and oral albendazole. Clinicopathologic correlation of the confocal scan was performed.

RESULTS

Corneal biopsy showed extracellular microsporidium spores aligned along keratocytes and corneal lamellae. In vivo confocal scans showed similar morphology, with bright dots aligned along keratocytes. Treatment with antimicrobials and topical steroid gave resolution of active keratitis, correlating with disappearance of the bright spores on repeat in vivo confocal scanning.

CONCLUSIONS

The in vivo confocal microscopy appearance of microsporidial keratitis corresponds to the histologic features from biopsy material. Treatment response may be monitored by using this technique, although definitive diagnosis requires corneal biopsy.

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).

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

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

Is microsporidial keratitis an emerging cause of stromal keratitis? A case series study

Background

Microsporidial keratitis is a rare cause of stromal keratitis. We present a series of five cases of microsporidial keratitis from a single centre in southern India with microbiologic and histopathologic features.

Case presentation

Patient charts of five cases of microsporidial stromal keratitis diagnosed between January 2002 and June 2004 were reviewed retrospectively for clinical data, microbiologic and histopathologic data. The presence of microsporidia was confirmed by special stains on corneal scrapings and/or corneal tissues, and electron microscopy. All patients were immunocompetent with a preceding history of trauma in three. Four patients presented with unilateral, small, persisting deep stromal infiltrates, of uncertain etiology, in the cornea, which were not responding to conventional antimicrobial treatment and required penetrating keratoplasty in three. Fifth case was unsuspected and underwent keratoplasty for post-traumatic scar. Three of five cases were diagnosed on corneal scrapings, prior to keratoplasty, while two were diagnosed only on histology. The microsporidia appeared as oval well defined bodies with dense staining at one pole. None of the patients showed recurrence following keratoplasty.

Conclusion

Microsporidia, though rare, should be suspected in chronic culture-negative stromal keratitis. Organisms could lie dormant without associated inflammation.

Zoonotic potential of the microsporidia

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

Trachipleistophora hominis infection in the myocardium and skeletal muscle of a patient with AIDS

OBJECTIVES

To review the literature relevant to microsporidial infection of muscle and to describe a case of human microsporidial infection involving both skeletal and cardiac muscle.

METHODS

Samples from an AIDS patient with myositis have been examined by light and electron microscopy.

RESULTS

We describe the findings at autopsy of a 47 year old Australian male with late stage AIDS, who had skeletal and cardiac muscle involvement with the microsporidian Trachipleistophora hominis. This is the third definitively identified case of human T. hominis infection and the first to describe infection of the myocardium.

CONCLUSIONS

Microsporidial infection of muscle is rare in humans, but more work is needed to elucidate both the organisms and routes of transmission of this group of parasitic protozoa.