Introduction

Microsporidia is a family of very rare, spore-forming organisms which tend to infect humans and animals. It was earlier classified under protozoans but has now been reclassified as fungi. Although a large family of 1,300 formally described species in 160 genera, only 13 species have been known to cause human disease.(1) These organisms most commonly involve the gastrointestinal tract followed by infection of the cornea, which is relatively rare, accounting for 0.4% of total cases presenting with keratitis. (2)

Case Presentations

Case 1

A 55 year old male patient, presented to the ophthalmology OPD with complaints of watering, irritation, redness and pain in the left eye since 10 days. He was not a known case of diabetes mellitus, HIV or tuberculosis. He denied any history of previous trauma and any similar complaints in the past. He had no history of fever. He had no history of similar complaints in the family.

On examination, right eye was normal, left eye examination showed edematous lids, circumcorneal congestion on conjunctiva and corneal sensations were intact [Fig 1]. Pupil reaction was sluggish. Cells and flare were seen in the left eye. Anterior chamber was quiet on examination.

Fig 1: Left eye showing edematous lids and circumcorneal congestion

Case 2

A 42 year old male patient, came to the ophthalmology OPD with similar complaints of redness and irritation in the left eye since 7 days. He had no history of trauma to the eye. He was not a known case of diabetes mellitus, HIV or tuberculosis and had no similar complaints in the past. No similar complaints in the family were found.

On examination right eye was normal. Left eye examination showed congestion on conjunctiva and mild discharge.

Slit lamp examination was performed in both patients which revealed coarse, raised punctate epithelial lesions with a typical stuck on appearance [Fig-2].

Corneal scrapings from both patients were sent to microbiology laboratory for staining and cultures.

On microscopy Gram stain showed plenty of inflammatory debris along with violet colored ovoid spores resembling Microsporidia (Fig 3.a, 3.b). On Giemsa stain, deep blue oval spore like structures were seen (Fig 3.c.). Modified Acid fast stain (1% H₂SO₄) showed acid fast, bright red spores against blue background (Fig 3.d). On slit lamp examination stuck on appearance in corneal stroma was seen.

Culture was done on Blood agar, MacConkey agar and Sabouraud dextrose agar which yielded no growth.

	Fig 2: Slit lamp examination revealing typical stuck on appearance
Fig 3a: Gram-stained smear showing violet-colored ovoid spores suggestive of Microsporidia (Gram stain, ×1000 magnification).	Fig 3b: Gram stained smear showing violet colored ovoid spores resembling Microsporidia (Gram stain, ×1000 magnification)
Fig 3c: Giemsa-stained smear showing deep blue oval spore-like structures suggestive of Microsporidia (Giemsa stain, ×1000 magnification).	Fig 3d: Modified Acid fast stained smear showing acid fast, bright red spores against blue background (Modified acid fast, ×1000 magnification)

Differential diagnosis: The cases of Microsporidial keratitis are quite difficult to diagnose as they resemble viral and fungal keratitis. Thorough investigations along with clinical findings aid in confirming the diagnosis which in turn helps to initiate appropriate therapy. The findings in these two cases along with the investigation reports strongly suggested Microsporidial keratitis.

Treatment and follow-up: The patients were started on fluconazole eye drops for 6 days, three times daily along with moxifloxacin eye ointment which had to be applied before bedtime. Patients were reviewed after 3 days of starting therapy and were symptomatically better and cornea was found to be clear.

Discussion

Microsporidial keratitis is increasingly recognized as an emerging cause of infectious keratitis and has gained considerable attention in recent years. Traditionally, Microsporidia were regarded as opportunistic pathogens that primarily affected immunocompromised individuals, particularly those with human immunodeficiency virus infection.(3) However, recent literature suggests a changing epidemiological trend, with a growing number of cases now being reported among immunocompetent individuals without identifiable systemic risk factors.(4) The present cases further support this observation, as both patients were immunocompetent and had no associated systemic illness or known ocular predisposing factors.

Clinically, microsporidial keratitis may present with a broad spectrum of manifestations ranging from superficial punctate keratoconjunctivitis to deeper stromal keratitis.(5) Because of this variability, the condition may easily mimic other forms of infectious keratitis, particularly viral or fungal keratitis, which often leads to delays in diagnosis and appropriate management.(2) Several studies have described the presence of coarse granular or “stuck-on” appearing stromal infiltrates as an important clinical clue suggestive of microsporidial infection.(6) Although this feature is not pathognomonic, its presence in unilateral, non-resolving keratitis should prompt clinicians to consider microsporidial infection in the differential diagnosis.(7)

Accurate diagnosis of microsporidial keratitis relies largely on microbiological confirmation. Conventional staining techniques such as Gram staining and modified acid-fast staining remain useful and practical methods for identifying the characteristic oval or ovoid spores of Microsporidia in corneal scrapings.(8) These techniques are particularly valuable in resource-limited settings where advanced diagnostic tools may not be readily available.(9) Although newer diagnostic modalities such as polymerase chain reaction (PCR), in vivo confocal microscopy, and metagenomic sequencing offer improved sensitivity and allow species-level identification, their use is often limited to specialized laboratories.(10)

Management of microsporidial keratitis continues to evolve with increasing awareness of the disease. Various therapeutic approaches have been described, including the use of topical antimicrobial agents such as voriconazole, fumagillin, and other azole antifungals.(11) In the present cases, both patients demonstrated a favorable clinical response following initiation of topical fluconazole therapy, which is consistent with outcomes reported in recent literature.(12) Early initiation of appropriate therapy is essential, as delayed diagnosis or inadvertent use of topical corticosteroids may worsen the infection and prolong the disease course.(13)

Despite increasing recognition, microsporidial keratitis remains under diagnosed due to its nonspecific clinical presentation and overlap with other infectious keratitis. Maintaining a high index of suspicion in cases of unilateral, non-resolving keratitis that do not respond to routine antibacterial or antiviral therapy is therefore essential for early diagnosis and timely management.

References

1. Chander J. Microsporidiosis. In Chander J, editor. Textbook of medical mycology. 4th ed. New Delhi: Jaypee Brothers Medical Publishers; 2018. p. 494-501.
2. Chou TY, Bansal J, Seidman R, et al. Bilateral microsporidial keratoconjunctivitis in a clinically healthy female receiving intravitreal steroid injections: associations and potential risk factors. Am J Ophthalmol Case Rep. 2022 Jul 9;27:101659.
3. Moshirfar M, Somani SN, Shmunes KM, et al. A narrative review of microsporidial infections of the cornea. Ophthalmol Ther. 2020;9(2):265-278.
4. Mohanty A, Sahu SK, Sharma S, et al. Past, present, and prospects in microsporidial keratoconjunctivitis: a review. Ocul Surf. 2023 Apr;28:364-377.
5. Matoba A, Goosey J, Chévez-Barrios P. Microsporidial stromal keratitis: epidemiological features, slit-lamp biomicroscopic characteristics, and therapy. Cornea. 2021 Dec 1;40(12):1532-1540.
6. Mohanty A, Behera HS, Barik MR, et al. Microsporidia-induced stromal keratitis: a new cause of presumed immune stromal keratitis. Br J Ophthalmol. 2023;107(5):607-613.
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8. Sharma S, Das S, Joseph J, et al. Microsporidial keratitis: need for increased awareness. Surv Ophthalmol. 2011 Jan-Feb;56(1):1-22.
9. Donthineni PR, Murthy SI, Joseph J, et al. Microsporidial stromal keratitis: an uncommon etiology of bilateral simultaneous corneal infection. Asian J Ophthalmol. 2020;17(3):311-317.
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11. Ramatchandirane B, Kumar MA, Marimuthu Y, et al. Successful treatment of microsporidial keratoconjunctivitis (MKC) with a combination of topical voriconazole 1% and gatifloxacin 0.5%: a large case series of 29 patients. Cureus. 2023 Nov 22;15(11):e49247.
12. Devi L, Prajna NV, Srinivasan M, et al. Microsporidial infection masquerading as graft rejection post-Descemet's stripping automated endothelial keratoplasty. Indian J Ophthalmol. 2017 Sep;65(9):869-871.
13. Mohanty A, Kelgaonkar A, Behera HS, et al. Microsporidia-associated anterior uveitis after keratoconjunctivitis. Cornea. 2023 Nov 1;42(11):1439-1445.