Microsporidia: Emerging Ocular Pathogens

Microsporidia are eukaryotic, spore forming obligate intracellular parasites, first recognized over 100 years ago.
Microsporidia are becoming increasingly recognized as infectious pathogens causing intestinal, ocular, sinus,
pulmonary, muscular and renal diseases, in both immunocompetent and immunosuppressed patients. Ocular
microsporidiosis, though uncommon, could be isolated or part of systemic infections. It occurs mainly in two forms:
keratoconjunctivitis form, mostly seen in immunocompromised individuals; stromal keratitis form seen in
immunocomptetant individuals. Recent reports indicate increasing number of cases of ocular microsporidiosis in
immunocompetent individuals. The ocular cases present as superficial keratitis in AIDS patients, and these differ in
presentation and clinical course from the cases seen in immunocompetent individuals which mainly appear to be as
deep stromal keratitis. For most patients with infectious diseases, microbiological isolation and identification techniques
offer the most rapid and specific determination of the etiologic agent, however this does not hold true for microsporidia,
which are obligate intracellular parasites requiring cell culture systems for growth. Therefore, the diagnosis of
microsporidiosis currently depends on morphological demonstration of the organisms themselves, either in scrapings
or tissues. Although the diagnosis of microsporidiosis and identification of microsporidia by light microscopy have
greatly improved during the last few years, species differentiation by these techniques is usually impossible and
electron microscopy may be necessary. Immuno fluorescent-staining techniques have been developed for species
differentiation of microsporidia, but the antibodies used in these procedures are available only at research laboratories
at present. During the last 10 years, molecular techniques have been developed for the detection and species
differentiation of microsporidia.

Although microsporidiosis can occur in people with normal immune systems, it is very uncommon. The symptoms of
microsporidiosis primarily occur in people with immune-system deficiency, such as HIV-infected individuals and
organ-transplant recipients.

Microsporidiosis can cause intestinal, lung, kidney, brain, sinus, muscle, or eye disease.  Intestinal symptoms that are
caused by microsporidia infection include chronic diarrhea, wasting, malabsorption, and gallbladder disease. In
patients with AIDS, the chronic diarrhea may be extremely debilitating and carries a significant mortality risk.

The majority of cases of intestinal microsporidiosis in AIDS patients are caused by Enterocytozoon bieneusi.  Lung
symptoms may include a cough and difficult, labored breathing. A chest X-ray may show signs of inflammation, fluid, or
cavities in the lungs.

Microsporidiosis can cause infection in the urinary tract, kidney failure, bladder inflammation, and bowel perforation.

Microsporidia can also spread throughout the body to cause inflammation in the brain, pancreas, sinuses, and muscle
tissue.  Eye infection with microsporidia can cause inflammation of the cornea and conjunctiva (keratoconjunctivitis).
Symptoms of ocular microsporidiosis may include eye pain, eye redness, or blurry vision.