Latent microsporidial infection in immunocompetent individuals - a longitudinal study

Microsporidia (Fungi) have been repeatedly identified as the cause of opportunistic infections predominantly in immunodeficient individuals such as AIDS patients. However, the global epidemiology of human microsporidiosis is poorly understood and the ability of microsporidia to survive and multiply in immunocompetent hosts remains unsolved. To determine the presence of latent microsporidia infections in apparently healthy humans in the Czech Republic, the authors tested sera, urine and stool originating from fifteen persons within a three month period examined on a weekly basis. Sera, stool and urine samples originating from fifteen HIV-negative people at risk with occupational exposure to animals, aged 22-56 years, living in the Czech Republic were tested by indirect immunofluorescence assay (IFA) for the presence of specific anti-microsporidial antibodies, standard Calcofluor M2R staining for the detection of microsporidian spores in all urine sediments and stool smears and molecular methods for the microsporidial species determination. Specific anti-microsporidial antibodies were detected in fourteen individuals, asymptomatic Encephalitozoon spp. infection was found in thirteen and E. bieneusi infection was detected in seven of those examined. While E. hellem 1A and E. cuniculi II were the major causative agents identified, seven different genotypes of E. bieneusi were recorded. These findings clearly show that exposure to microsporidia is common and chronic microsporidiosis is not linked to any clinical manifestation in healthy population. Moreover, our results indicate much higher incidence of microsporidial infections among an apparently healthy population than previously reported. These results open the question about the potential risk of reactivation of latent microsporidiosis in cases of immunosupression causing life-threatening disease.