Microsporidiosis

Microsporidiosis is an infectious disease caused by microsporidia, a group of obligate intracellular parasitic fungi belonging to the phylum Microsporidia. Over 1,400 species have been identified, but only about 17 species are known to infect humans, with Enterocytozoon bieneusi and Encephalitozoon intestinalis being the most commonly implicated. Microsporidia can affect multiple organ systems, including the gastrointestinal tract, eyes, respiratory system, urinary tract, muscles, and central nervous system. The disease predominantly affects immunocompromised individuals, particularly those with HIV/AIDS, organ transplant recipients on immunosuppressive therapy, and other individuals with weakened immune systems, though cases in immunocompetent persons have also been reported. The most common clinical presentation is chronic watery diarrhea, which can be severe and debilitating, leading to significant weight loss, malabsorption, and dehydration, especially in immunocompromised patients. Ocular microsporidiosis, typically caused by Encephalitozoon species or Vittaforma corneae, manifests as keratoconjunctivitis with symptoms of eye pain, redness, photophobia, and decreased visual acuity. Disseminated disease can involve the sinuses (sinusitis), kidneys (nephritis), liver (hepatitis), brain (encephalitis), and skeletal muscles (myositis). In immunocompetent individuals, the infection is often self-limiting, primarily presenting as self-resolving diarrhea or ocular disease. Treatment depends on the infecting species and the patient's immune status. Albendazole is effective against most Encephalitozoon species and is considered first-line therapy for many forms of microsporidiosis. However, Enterocytozoon bieneusi, the most common species causing intestinal disease, responds poorly to albendazole; fumagillin has shown efficacy but is associated with significant side effects including thrombocytopenia. For HIV-infected patients, immune reconstitution through antiretroviral therapy (ART) is a critical component of management and can lead to resolution of infection. Topical fumagillin eye drops have been used for ocular microsporidiosis. Prognosis is generally favorable with appropriate treatment and immune restoration, but the disease can be life-threatening in severely immunocompromised individuals if left untreated.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

Common questions about Microsporidiosis