Latent Microsporidial Infection in Immunocompetent Individuals – A Longitudinal Study

Abstract

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. Microsporidia are a group of obligate intracellular parasitic fungi that have risen over the past two decades from obscure organisms to well recognized human pathogens. Out of 14 species reported to infect humans and causing more severe symptoms in immunocompromised individuals, microsporidia of the species Encephalitozoon and Enterocytozoon bieneusi are the most frequent causes of life-threatening chronic diarrhea and systemic disease in HIV patients and acute, self-limited diarrhea in immunocompetent persons. Although the diagnosis and clinical management of microsporidiosis cases have improved significantly recently, the epidemiology of human microsporidiosis is still unclear. To identify the occurrence of latent microsporidia infections in apparently healthy people, the authors tested sera, urine and stool originating from fifteen persons within a three month period. They found specific antibodies against microsporidia in sera originating from fourteen individuals, and using molecular tools, they detected microsporidial infection intermittently in all tested people. The presence of detectable amounts of microsporidial spores demonstrated that exposure to microsporidia is more common than previously believed and microsporidiosis is not linked to any clinical manifestations in healthy people. This finding should make the clinician more aware of the risk of this unapparent infection, its potential reactivation after immunosupression and consequences leading to life-threatening disease.