Microsporidial Keratitis

Abstract

Hundreds of genera and thousands of species of obligate intracellular spore forming eukaryotes constitute the phylum Microspora. Currently these organisms are known to cause infections in the immunocompromised individuals in whom they exhibit diverse clinical manifestations including pulmonary, ocular, intestinal, muscular and renal disease. Ocular microsporidiosis can present as an isolated entity or as a part of systemic infection. Infection is acquired by traumatic inoculation or by contact with contaminated soil or water. Clinically this infection can present as stromal keratitis, scleritis, keratoconjuntivitis and endophthalmitis. Seven genera have been found to be associated with human ocular infections. Infections by these pathogenic organisms involve unique pathogenic mechanism-injection of the sporoplasm in the host cell via polar tube. Protean clinical manifestations and resemblance to herpetic keratitis poses as a challenge in clinical diagnosis of this condition. Diagnosis therefore mainly depends on morphological demonstration of these organisms. Electron microscopy is the 'gold standard' diagnostic method to detect microsporidial spores. Molecular methods like PCR, real time PCR are sensitive tests and aids in identification till the species level. Drugs like albendazole and fumagillin are widely used to treat microsporidial keratitis. Penetrating keratoplasty is useful in treating medically non responding cases.

A Narrative Review of Microsporidial Infections of the Cornea

“…Microsporidial stromal keratitis (MSK) is rarer than superficial keratoconjunctivitis and occurs predominantly in immunocompetent individuals. MSK follows a slow-growing, insidious course, with symptoms ranging from 1 month to 2 years prior to the initial presentation [3]. MSK typically occurs secondary to Vittaforma corneae (previously Nosema corneum) or Microsporidium [15,43].…”

“…Acute [42] Delayed [3] Clinical presentation Photophobia, redness, tearing, foreign body sensation, impaired visual acuity, eye pain [4,31,42] Slit-lamp findings Grayish-white, coarse, multifocal, raised epithelial lesions and non-purulent conjunctivitis ? central epithelial lesions ?…”

“…Some immunofluorescent antibody techniques have been developed for the detection of Encephalitozoon species spores, though they are less convenient compared with traditional chromotrope and fluorochromes. Moreover, reagents for immunofluorescence staining of microsporidial spores may have low specificity because of background staining and cross-reactions with yeast and bacteria [3]. Lastly, these techniques are not yet readily available in many laboratory settings.…”

“…Microsporidia are unicellular, obligate intracellular, eukaryotic parasites that belong to the phylum Microspora and subkingdom Protista [1,2]. Microsporidia are true eukaryotes due to the presence of a nucleus with a nuclear envelope, chromosome separation on mitotic spindles, and an intracytoplasmic membrane system [3]. Unlike most eukaryotes, however, microsporidia lack typical mitochondria, peroxisomes, and centrioles.…”

Molecular identification of microsporidian species in patients with epithelial keratitis

“…The phylum Microsporidia is a large group composed of more than 200 genera and 1200 species, with many more likely awaiting discovery [3,23]. At least the following seven genera, Enterocytozoon, Encephalitozoon, Pleistophora, Traphipleistophora, Brachiola, Nosema and Vittaforma, have been described as the causative agents in human ocular infections [24,25]. It is well known that the superficial keratoconjuntivitis is caused by Encephalitozoon intestinalis and E. hellem.…”