Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Microsporidia are highly specialized fungi that cause a wide variety of clinical syndromes in humans. The most common microsporidia are Enterocytozoon bieneusi and Encephalitozoon intestinalis, which infect the gastrointestinal tract and cause a diarrheal illness, and Encephalitozoon cuniculi and Encephalitozoon hellem, which can infect the conjunctiva, respiratory tract, and genitourinary system. Human infections have been reported most frequently in patients with AIDS, but also can occur in other immunocompromised patients, including solid organ allograft recipients and, sporadically, immunocompetent hosts. Less commonly, other microsporidia such as Vittaforma corneae and Brachiola species can cause disseminated or organ-specific disease. Diagnosis of microsporidiosis is traditionally performed by light microscopic examination of stool, urine, and other specimens using a strong trichrome (chromotrope 2R) stain for detection of the characteristic spores. Unfortunately microscopic identification can be challenging due to the small size of the spores (1-4 micrometer) and their resemblance to yeast. Molecular detection using species-specific PCR offers improved sensitivity and specificity and is available for the microsporidia that cause the majority of intestinal and renal infections (ie, Encephalitozoon species and Enterocytozoon bieneusi). The microsporidia stain is reserved for use with other (non-stool and non-urine) specimen sources due to the variety of other species that may be detected outside of the intestinal tract and kidney.
The antihelmintic drug, albendazole has been found effective in some infections due to Enterocytozoon bieneusi and Encephalitozoon (Septata) intestinalis.
Diagnosis of extra-intestinal microsporidiosis involving the lung, skin, and other organs, particularly in immunocompromised hosts
Diagnosis of ocular microsporidiosis
A positive result suggests an active or recent infection. Results should be correlated with the patient’s clinical presentation and immune status.
A negative result indicates absence of detectable microsporidial spores in the specimen, but does not always rule out ongoing microsporidiosis since the organism may be present at very low levels or shed sporadically.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
These organisms are very difficult to identify among the multitude of organisms and artifactual debris present in the stool.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
If positive, reported as Microsporidia detected
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Weber R, Bryan RT, Schwartz DA, Owen RL: Human microsporidial infections. Clin Microbiol Rev 1994;7:426-461
2. Goodgame RW: Understanding intestinal spore-forming protozoa: cryptosporidia, microsporidia, isospora, and cyclospora. Ann Intern Med 1996;124:429-441
3. Wanke CA, DeGirolami P, Federman M: Enterocytozoon bieneusi infection and diarrheal disease in patients who were not infected with human immunodeficiency virus: case report and review. Clin Infect Dis 1996;23:816-818