Bilateral microsporidial keratoconjunctivitis in an immunocompetent non-contact lens wearer

The microsporidian polar tube: origin, structure, composition, function, and application

Microsporidia are a class of obligate intracellular parasitic unicellular eukaryotes that infect a variety of hosts, even including humans. Although different species of microsporidia differ in host range and specificity, they all share a similar infection organelle, the polar tube, which is also defined as the polar filament in mature spores. In response to the appropriate environmental stimulation, the spore germinates with the polar filament everted, forming a hollow polar tube, and then the infectious cargo is transported into host cells via the polar tube. Hence, the polar tube plays a key role in microsporidian infection. Here, we review the origin, structure, composition, function, and application of the microsporidian polar tube, focusing on the origin of the polar filament, the structural differences between the polar filament and polar tube, and the characteristics of polar tube proteins. Comparing the three-dimensional structure of PTP6 homologous proteins provides new insight for the screening of additional novel polar tube proteins with low sequence similarity in microsporidia. In addition, the interaction of the polar tube with the spore wall and the host are summarized to better understand the infection mechanism of microsporidia. Due to the specificity of polar tube proteins, they are also used as the target in the diagnosis and prevention of microsporidiosis. With the present findings, we propose a future study on the polar tube of microsporidia.

Past, present, and prospects in microsporidial keratoconjunctivitis- A review

Ocular microsporidiosis comprises two entirely different spectra of disease as keratoconjunctivitis and stromal keratitis. Microsporidial keratoconjunctivitis (MKC) has been increasingly reported in the past two decades, probably due to raised awareness, simpler diagnostic procedures, and a better understanding of the clinical presentation. It is characterized by the presence of raised, coarse, punctate, multifocal, round to oval, greyish-white corneal epithelial lesions which usually evolve into nummular scars before resolution. Conjunctivitis seen is non-purulent and of mild-moderate intensity, with mixed papillary-follicular reaction. The mode of transmission and pathogenesis is poorly understood. Despite lack of inflammatory response, uncommon associations reported were- endotheliitis, corneal edema, limbitis, uveitis, and sub-epithelial infiltrates. There has been no consensus on the management of MKC. It varies from the use of multiple antimicrobial agents to simple lubricants. The majority of the disease goes underdiagnosed or misdiagnosed and treated as adenoviral keratoconjunctivitis, with topical steroids or anti-virals empirically. Changing trends have been noticed in the pattern of infection, possibly with increasing evidence of Vittaforma corneae as causative organisms, previously reported to cause stromal keratitis. An elaborate review of the past and present literature on MKC is provided in this review article, along with gaps in knowledge, and future directions of research.

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.

Sequelae of microsporidial keratoconjunctivitis and its management

Purpose:

To characterize the sequelae of microsporidia keratoconjunctivitis (MKC) and outline its management.

Methods:

Retrospective analysis of microbiologically proven MKC returned with persistent disease between January 2015 and December 2019 was done. Demographics, clinical features, management, and outcome were analyzed.

Results:

Sixteen patients (21 eyes) of 332 treated for MKC returned with the persisting disease. The mean age of 11 males (68.7%), and 5 females was 35.1 ± 12.2 years. Three-quarter of them did not have a known predisposing risk factor and one-quarter of them were referred for chronic conjunctivitis. Past medications included topical antivirals (n = 8) and topical corticosteroid (n = 6). Three predominant presentations were persistent (>3 weeks) superficial punctate keratitis (SPKs, n = 7), sub-epithelial infiltrates (SEIs, n = 13), and uveitis (n = 2). The lesions recurred in eight eyes (SPK and SEI 4 each) after a disease-free interval of 60.4 ± 40.6 days; there were 13 episodes of recurrence. Topical low potent corticosteroids (loteprednol/fluorometholone), and tacrolimus ointment 0.03% were used in 17 (80.9%) and 8 (38%) eyes, respectively, for a mean duration of 44.8 ± 31.6 and 226.8 ± 180.5 days, respectively. At follow-up, 172.3 ± 183.6 days, visual recovery was statistically significant in persistent eyes (BCVA 0.07 ± 0.07 logMAR; P < 0.00001) but, not in recurrent eyes (BCVA 0.16 ± 0.08 logMAR; P = 0.07). Five of 21 eyes were left with residual significant scar.

Conclusion:

The sequelae of microsporidial keratoconjunctivitis are not uncommon. Topical 0.03% tacrolimus ointment appeared to be an effective corticosteroid-sparing agent for the treatment of SEIs and prevention of recurrence.

Clinical Profile of Bilateral Microsporidial Keratoconjunctivitis in Healthy Individuals-A Case Series With Long-term Follow-up

PURPOSE

To describe bilateral microsporidial keratoconjunctivitis in healthy individuals with long-term follow-up.

METHODS

Six cases of smear-positive bilateral microsporidial keratoconjunctivitis were diagnosed and followed up during the study period August 2017 to January 2019. Associated risk factors, clinical features, coexistence with adenovirus, clinical course, and recurrence were studied.

RESULTS

The mean age was 36.6 years (range: 10-65 years). The mean duration of symptoms was 13.6 days (range: 7-60 days). Predisposing risk factors were present in 4 of 6 cases. The best-corrected visual acuity at presentation was ≥20/30 in all eyes except in one. Typical microsporidial epithelial lesions were seen in only one case. Persistent lesions, clinically resembling Thygeson superficial punctate keratitis in both eyes, were observed in 3 cases. The lesions in 5 eyes resolved with topical lubricants, and the remaining 7 eyes were treated with topical steroids and tacrolimus 0.03%. Complete resolution was seen in 5 eyes at the end of 1 month, and superficial scarring at the last follow-up was seen in 5 eyes. The best-corrected visual acuity was ≤20/30 in 3 eyes at the last follow-up. The mean duration of follow-up was 7.3 months (range: 3-12 mo).

CONCLUSIONS

Bilateral microsporidial keratoconjunctivitis in healthy patients has an atypical presentation with prolonged course. Microsporidia could be implicated as potential candidates in the etiopathogenesis of Thygeson superficial punctate keratitis.

Vittaforma Corneae keratoconjunctivitis: An emerging pathology among travelers returning from Southeast Asia

Microsporidium keratoconjunctivitis is an very rare disease. It is related to outbreaks in Asia due to exposure to contaminated water or soil. Microsporidium keratoconjunctivitis is a a self-limited disease, but it could have long term courses. We present the case of a 29 year old woman who started with pain, redness and blurred vision after a holiday in Singapore and did not respond to conjunctivitis treatment. PCR sequencing and PAS staining of corneal epithelial biopsy identified Vittaforma corneae as the causative organism. Treatment was initiated with corneal debridement, oral albendazol, and intensive topical voriconazole, levofloxacin and propamidine, but the conjunctival and corneal disease was only resolved 5 months later with the introduction of topical steroids to treat her severe limbitis. Suspicion of Microsporidium keratoconjunctivitis should be raised amongst ophthalmologists in unilateral keratitis with mild conjunctivitis in travelers from Asia.

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.

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.

Diagnosis and treatment of microsporidial keratoconjunctivitis: literature review and case series

Purpose

The purpose of this study is to describe the clinical characteristics, microscopic findings, and treatment response to albendazole of microsporidial keratoconjunctivitis among immunocompromised individuals with HIV/AIDS.

Methods

This is a retrospective case series. Diagnosis of microsporidial keratoconjunctivitis was confirmed by subspecialist examination and conjunctival swabs examined by light microscopy. HIV infection was documented, and absolute CD4+ T cell count was determined. Patients were treated with albendazole and followed for clinical response.

Results

Light microscopy from the conjunctival swabs demonstrated myriad small, round to oval microsporidial organisms that stained positively with modified acid-fast methods. Two of the patients initially not taking highly active antiretroviral therapy (HAART) and presenting with an absolute CD4+ T cell count less than 100 cells/μL had a more severe form of keratoconjunctivitis than the third patient (receiving HAART, with a CD4+ T cell count of 259 cells/μL). All patients were started or continued on HAART. Two of the patients responded to oral albendazole, with resolution of symptoms and signs. The third patient did not initially respond, perhaps because of an immune recovery inflammatory syndrome, but subsequently had temporary improvement with albendazole.

Conclusions

Microsporidial keratoconjunctivitis is a rare ocular complication of HIV/AIDS. Light microscopic evaluation of conjunctival swabs may be a useful minimally invasive first step toward diagnosis of microsporidial keratoconjunctivis in settings where electron microscopy is not available. Based on the limited available information, albendazole often is effective for this condition, and is widely available in developing countries at low cost.

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.

Clinical and Microbiological Profile of Microsporidial Keratoconjunctivitis in Southern India

PURPOSE

To report the clinical and microbiological profile of microsporidial keratoconjunctivitis in immunocompetent individuals in southern India.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS

Nineteen cases of microsporidial keratoconjunctivitis diagnosed between January 2002 and December 2004 were studied.

METHODS

All medical and laboratory records of patients with infectious keratitis during the study period were reviewed. In all cases, after relevant history recording and slit-lamp examination, corneal/conjunctival scrapings were collected. Multiple scrapings were taken from the lesions and examined by fluorescence or light microscopy after staining with potassium hydroxide and calcofluor white (KOH + CFW), Gram's stain, Kinyoun's, and Giemsa stain. In some cases, the serum was tested for human immunodeficiency virus antibody by enzyme-linked immunosorbent assay.

MAIN OUTCOME MEASURES

Clinical course, demographic features, predisposing factors, microbiological profile, treatment, and final outcome.

RESULTS

Of 4822 cases of suspected microbial keratitis seen during the period, 19 (0.4%) were identified as microbiologically proven microsporidial keratitis. All patients were apparently healthy; 8 had a history of ocular trauma, and 3 mentioned bathing in unclean river water. All but 2 had unilateral involvement. The mean age of the patients was 38.4+/-13.7 years (range, 23-73). The duration of symptoms ranged from 1 day to 2 years, with 11 of 19 (58%) presenting within a week of onset of symptoms. Slit-lamp examination revealed multifocal, coarse, punctate, raised epithelial lesions in all patients. A mild to moderate nonpurulent conjunctivitis was present in all cases, with papillary and/or follicular reaction in 14. Corneal/conjunctival scrapings demonstrated microsporidial spores by KOH + CFW in 16 of 17 cases tested, whereas the diagnosis was made by Giemsa stain in 2 cases and by Gram's stain in one. Kinyoun's (1% acid fast) stain was confirmatory in all cases. In all patients, treatment was started after debridement and included oral and/or topical antimicrobial agents. At last follow-up, 15 of 19 achieved a visual acuity of 20/20.

CONCLUSIONS

Microsporidial keratoconjunctivitis should be considered in the differential diagnosis of atypical punctate epithelial keratitis associated with conjunctivitis and can be diagnosed by routine microbiological methods. The disease can occur in healthy individuals, and the outcome of treatment is often satisfactory.

Identification of a new spore wall protein from Encephalitozoon cuniculi

Microsporidia form environmentally resistant spores that are critical for their host-to-host transmission and persistence in the environment. The spore walls of these organisms are composed of two layers, the exospore and the endospore. Two spore wall proteins (SWP1 and SWP2) have been previously identified in members of the Encephalitozoonidae family. These proteins localize to the exospore. The endospore is known to contain chitin, and a putative glycosylphosphatidylinositol (GPI)-anchored chitin deacetylase has been localized to the plasmalemma-endospore interface. Using proteomic techniques, we have identified a new spore wall protein (SWP3) that is located in the endospore. The gene for this protein is located on chromosome 1 and corresponds to the open reading frame ECU01_1270. SWP3 is predicted to have a signal peptide and to be GPI anchored. Consistent with these modifications, two-dimensional electrophoresis demonstrated that SWP3 has an acidic pI and a molecular mass of <20 kDa. By immunoelectron microscopy, this protein was found on the cell surface during sporogony and in the endospore in mature spores. SWP3 has several potential O-glycosylation sites, and it is possible that it is a mannosylated protein like the major polar tube protein (PTP1).

Enterocytozoon bieneusi (microsporidia) in clinical samples from immunocompetent individuals in Tenerife, Canary Islands, Spain

Microsporidia are newly emerging pathogens of humans and animals, with Enterocytozoon bieneusi being the most common causal agent in human microsporidiosis. To determine the presence of E. bieneusi, 273 clinical samples (40 urine, 156 stools, 37 sputum, 9 bronchial aspirates, 5 bronchial washes and 26 pleural fluids) from immunocompetent patients, mainly suffering diarrhoea or pneumonia, in Tenerife, Canary Islands, Spain were analysed using light microscopy after staining with Weber's chromotrope and by PCR/hybridisation with a specific probe designed to increase the sensitivity of the identification. In this study, detection of E. bieneusi after PCR/hybridisation is reported in 18 (11.54%) of 156 stool samples, 1 (2.5%) of 40 urine samples and 6 (16.22%) of 37 sputum samples. To our knowledge, these are the first reports of E. bieneusi in this subtropical region, showing the increased importance of these parasites as emerging pathogens worldwide.

The microsporidian polar tube: a highly specialised invasion organelle

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

Zoonotic potential of the microsporidia

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

Epidemiology of microsporidiosis: sources and modes of transmission

Microsporidia are single-celled, obligate intracellular parasites that were recently reclassified from protozoa to fungi. Microsporidia are considered a cause of emerging and opportunistic infections in humans, and species infecting humans also infect a wide range of animals, raising the concern for zoonotic transmission. Persistent or self-limiting diarrhea are the most common symptoms associated with microsporidiosis in immune-deficient or immune-competent individuals, respectively. Microsporidian spores appear to be relatively resistant under environmental conditions, and species of microsporidia infecting humans and animals have been identified in water sources, raising concern about water-borne transmission. Sensitive and specific immunomagnetic bead separation and PCR-based methods are being developed and applied for detecting microsporidia in infected hosts and water sources for generating more reliable prevalence data. The most effective drugs for treating microsporidiosis in humans currently include albendazole, which is effective against the Encephalitozoon species but not against Enterocytozoon bieneusi, and fumagillin, which has broader anti-microsporidia activity but is toxic in mammals, suggesting a need to identify better drugs. Strategies to capture and disinfect microsporidia in water are being developed and include filtration, coagulation, chlorination, gamma-irradiation, and ozonation.