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Case Study: September 2006
History
A 35 year old male presented to eye casualty with a short history of painful, red, watery eyes, with blurred vision. On examination, the visual acuity was 6/12 (left and right). Slit lamp examination revealed bilateral, superficial punctate keratoconjunctivitis. The patient was not immuno-compromised. The ophthalmologist performed a corneal scrape and fixed the slides in methanol. One of the slides was stained with a modified Ziehl-Neelsen stain. This showed 3-5 micron pink, oval organisms (fig 1).In the light of the appearances in fig 1, material was lifted off one of the other methanol fixed slides and exposed to transmission electron microscopy. Figure 2 and 3 show two views of this infective agent. The arrows point to distinctive features.
Questions
1.What is the diagnosis?
2.Which other tinctorial stains can be employed to detect this infective agent on corneal scrapes or conventional histological sections?
3.Which predominant form of this infective agent is seen in the Figures?
4.What are the two main ophthalmic presentations of this infection and what do these two clinical presentations reflect?
1. Bilateral corneal microsporidiosis.
2. -Potassium hydroxide plus calcofluor white (KOH+CFW), viewed under -fluorescence.
-Gram
-Giemsa
-Modified Ziehl-Neelsen (1% H2SO4, cold)
3. Spore form.
4. Superficial punctate keratoconjunctivitis.
Corneal stromal keratitis.
The two presentations reflect the genus involved as well as the immune status of the patient.
The cornea and microsporidiosis- a brief summary.
Microsporidia are eukaryotic, spore forming obligate intracellular parasites. Ocular microsporidiosis can be isolated or part of a systemic infection.
Known clinical presentations: Superficial punctate keratoconjunctivitis and corneal stromal keratitis. This reflects the type and immune status of the patient. Superficial punctate keratoconjunctivitis-tends to affect immunocompromised patients or those wearing contact lenses. However, many cases now emerging in immunocompetent patients. Corneal stromal keratitis generally in immunocompetent patients.
Microsporidia species detected in corneal tissue: Encephalitozoon hellum, cuniculi and intestinalis, Vittaforma cornea, Trachipleistophora hominis, Microsporidium africanum, Microsporidium ceylonensis, Nosema ocularum and Brachiola algerae, to date.
Taxonomic classification: Encephalitozoon, Enterocytozoon, Trachipleistophora, Pleistophora Vittaforma, Nosema , ‘Microsporidium’
First published ocular case of Microsporidiosis:
Ashton N, Wirashinha PA. Encephalitozoonosis (Nosematosis) of the cornea. Br J Ophathalmol 1973;57 :669-74.
Ocular transmission: Uncertain. Superficial presentations suggest direct inoculation, as in this case.
Parisitology: schizogenic phase and the sporulation (sporogenic) phase.Spores vary from 1 micron to 20 microns.
Diagnostic aspects:
Light microscopy: Gram stain: oval, gram positive spores, like yeasts. However, non-budding and 1% acid fast stain, stains them pink-red, with or without a distinctive equatorial line.
Calcofluor white, Giemsa and polyclonal / monoclonal immunofluorescent approaches also useful.
Transmission electron microscopy Often gold standard that allows genus and species identification. Highly specific.Shows up the exospore, endospore, manubrium, nucleus, polaroplast, polar sac, posterior vacuole and coils of polar tube. Figures B and C show the coils of the polar tube cut longitudinally (fig 1) and transversly (fig 2). The other details are less clear because the corneal smears were fixed in methanol.
PCR also very useful
