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

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.

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.

A Narrative Review of Microsporidial Infections of the Cornea

Microsporidia are a rare and commonly misdiagnosed cause of corneal infection, accounting for approximately 0.4% of cases of microbial keratitis in some populations. Ocular microsporidiosis most often presents as either microsporidial keratoconjunctivitis (MKC) or microsporidial stromal keratitis (MSK). Though these two clinical entities exhibit similar symptomology, they are distinguished from one another by the time course for disease progression, findings on slit-lamp examination, and response to medical therapy. This review summarizes the current literature on the etiology and clinical presentation of microsporidial infections of the cornea and highlights ongoing developments in available diagnostic modalities and treatment regimens.

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.

Microsporidial keratitis retrospectively diagnosed by ultrastructural study of formalin-fixed paraffin-embedded corneal tissue: a case report

Background

The utility of formalin-fixed paraffin-embedded (FFPE) corneal tissue specimens for retrospective diagnosis of microsporidial keratitis was evaluated by transmission electron microscopy (TEM) analysis and the possible second case of microsporidial keratitis after Descemet stripping automated endothelial keratoplasty (DSAEK) was described.

Case presentation

A 68-year-old man presented with multiple crystalline opacities in the corneal stroma that progressed extremely slowly after DSAEK. Fungiflora Y staining of corneal scrapings from the affected regions revealed an oval microorganism. Topical voriconazole administration was ineffective and penetrating keratoplasty was performed. Histological and molecular analyses were carried out on the excised cornea. Ziehl–Neelsen staining revealed an acid-fast, oval organism that was visible by ultraviolet illumination after Fungiflora Y and Uvitex 2B staining, whereas periodic acid-Schiff and Grocott’s staining did not yield any significant findings. Microsporidium was detected by TEM of FFPE tissue. Nosema or Vittaforma sp. was suspected as the causative microorganism by PCR of FFPE tissue and by the fact that those species are known to cause eye infection. The corneal graft has maintained transparency at 1 year and half postoperatively.

Conclusions

This is the first known case of microsporidial keratitis diagnosed retrospectively by molecular and ultrastructural study of FFPE tissue, and the possible second case of microsporidial keratitis after DSAEK. Microsporidial keratitis should be considered when corneal opacity refractory to conventionally known therapy would occur after DSAEK. Our findings suggest that more microsporidial keratitis cases than have been reported to date can be identified by TEM or PCR examination of FFPE corneal specimens.

Exotic Tourist Destinations and Transmission of Infections by Swimming Pools and Hot Springs-A Literature Review

A growing number of people undertake international travel, and yet faster growth of such travel is expected in the tropics. Information on the hazards presented by pool and hot spring waters in tropical countries is very limited. This review aims to collate available information on pool water quality, alongside data on cases and outbreaks associated with swimming in pools in tropical regions affecting both local populations and travellers. Bacteria species commonly causing cases and outbreaks in the tropics as well as elsewhere in the world were excluded, and the review focuses on studies related to pathogens that, with the exception of Cryptosporidium, are unusual in more temperate climates. Studies concerning subtropical countries were included in the light of climate change. Diseases transmitted by vectors breeding in poorly maintained, neglected or abandoned pools were also included. 83 studies dealing with Microsporidia, Leptospira spp., Schistosomas spp., Cryptosporidium spp., Acanthamoeba spp., Naegleria spp., Clostridium trachomatis, viruses, and vectors breeding in swimming pool and hot tub waters, and fulfilling predefined criteria, have been included in our survey of the literature. In conclusion, prevention strategies for pool safety in the tropics are imperative. Public health authorities need to provide guidance to westerners travelling to exotic destinations on how to protect their health in swimming pools.

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.

A study of microsporidiosis in corneal scrapings of keratitis patients referring to Farabi Eye Hospital, Tehran, Iran in 2013-14

Background and Purpose:

Microsporidiosis is one of the emerging and opportunistic infections, which causing various clinical symptoms in humans. The prevalence of this infection varies, depending on the infected organ, diagnostic methods, and geographical conditions. In the present study, we aimed to investigate microsporidial keratitis in patients referring to Farabi Eye Hospital Tehran, Iran in 2013-14.

Materials and Methods:

Two scraping samples were collected from 91 keratitis patients, five cases had prior history of receiving immune suppressive drugs. One of the two collected samples from each participant was used for Vero cell culture and the other was used for the preparation of Giemsa and Gram staining slides. After 30 days, the cells were scrapped and used for DNA extraction; afterwards, nested polymerase chain reaction (PCR) detection method was applied. Primer pairs of small-subunit ribosomal RNA gene were designed by CLC Genomics workbench software to amplify all major microsporidian pathogens, as well as E. bieneusi , which was used as the positive control in this study.

Results:

The nested PCR showed negative results regarding the presence of microsporidia in the samples. Similarly, Giemsa and Gram staining slides did not detect any spores.

Conclusion:

The prevalence of human microsporidiosis ranges between 0% and 50%, worldwide. Based on all the negative samples in the present study, we can conclude that the prevalence of this infection among Iranian patients falls in the lower quartile. By gathering further evidence, researchers can take a step forward in this area and open new doors for the assessment of AIDS patients and users of immunosuppressive drugs.

Microsporidial keratitis: Literature review and report of 2 cases in a tertiary eye care center

Microsporidia are getting more recognized as causative organism of ocular, gastrointestinal, renal, pulmonary, and sinus diseases, in both immunocompetent and immunosuppressed patients. Ocular microsporidiosis can be isolated or may present as part of systemic infection. Recent reports showed increasing number of cases of ocular microsporidiosis in immunocompetent individuals. The ocular type occurs mainly in two forms: keratoconjunctivitis form which is mostly seen in immunocompromised individuals and stromal keratitis form seen in immunocompetent individuals. The ocular cases which present with superficial keratitis in acquired immune deficiency syndrome (AIDS) patients differ from the cases seen in immunocompetent individuals which present mainly as deep stromal keratitis. We are presenting the only two documented cases of microsporidial keratitis diagnosed over 25 years of practice in our institution. The cases are diagnosed by identification of the Acid-fast organisms. Ultrastructure and additional information on species identification in one of the cases. Both cases are eventually managed by therapeutic PKP. Diagnosis and treatment modalities are discussed based on a comprehensive literature review.

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.

Importance of nonenteric protozoan infections in immunocompromised people

There are many neglected nonenteric protozoa able to cause serious morbidity and mortality in humans, particularly in the developing world. Diseases caused by certain protozoa are often more severe in the presence of HIV. While information regarding neglected tropical diseases caused by trypanosomatids and Plasmodium is abundant, these protozoa are often not a first consideration in Western countries where they are not endemic. As such, diagnostics may not be available in these regions. Due to global travel and immigration, this has become an increasing problem. Inversely, in certain parts of the world (particularly sub-Saharan Africa), the HIV problem is so severe that diseases like microsporidiosis and toxoplasmosis are common. In Western countries, due to the availability of highly active antiretroviral therapy (HAART), these diseases are infrequently encountered. While free-living amoebae are rarely encountered in a clinical setting, when infections do occur, they are often fatal. Rapid diagnosis and treatment are essential to the survival of patients infected with these organisms. This paper reviews information on the diagnosis and treatment of nonenteric protozoal diseases in immunocompromised people, with a focus on patients infected with HIV. The nonenteric microsporidia, some trypanosomatids, Toxoplasma spp., Neospora spp., some free-living amoebae, Plasmodium spp., and Babesia spp. are discussed.

Optimal CD8 T-cell response against Encephalitozoon cuniculi is mediated by Toll-like receptor 4 upregulation by dendritic cells

CD8+ T-cell immunity has been shown to play an important role in the protective immune response against Encephalitozoon cuniculi. Although earlier studies suggest that dendritic cells (DC) are important for the induction of this response, the factors responsible for initiation of the dendritic cell response against this pathogen have not been evaluated. In the current study, we demonstrate that E. cuniculi infection causes strong Toll-like receptor 4 (TLR4)-dependent dendritic cell activation and a blockade of this molecule reduces the ability of DC to prime an antigen-specific CD8+ T-cell response. Pretreatment of DC with anti-TLR4 antibody causes a defect in both in vitro and in vivo CD8+ T-cell priming. These findings, for the first time, emphasize the contribution of TLR4 in the induction of CD8+ T-cell immunity against E. cuniculi infection.

Phylogenetic characterization of Encephalitozoon romaleae (Microsporidia) from a grasshopper host: relationship to Encephalitozoon spp. infecting humans

Encephalitozoon species are the most common microsporidian pathogens of humans and domesticated animals. We recently discovered a new microsporidium, Encephalitozoon romaleae, infecting the eastern lubber grasshopper Romalea microptera. To understand its evolutionary relationships, we compared partial gene sequences of alpha- and beta-tubulin and methionine aminopeptidase 2 enzyme from this and related species. We also analyzed the rRNA internal transcribed spacer. Based on tubulin and MetAP-2 gene phylogenetic analysis, E. romaleae clustered with the Encephalitzoon group with strong bootstrap support (>99%). Within the Encephalitozoon clade, E. romaleae clustered with Encephalitozoon hellem for both the beta-tubulin and MetAP-2 phylogenies based on ML tree. The alpha-tubulin based ML tree, however, placed the new microsporidium closer to Encephalitozoon cuniculi. The rRNA internal transcribed spacer region of E. romaleae has 91% homology with E. hellem.

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.