Latent microsporidial infection in immunocompetent individuals - a longitudinal study

BACKGROUND

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.

AIMS

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Antibodies enhance the protective effect of CD4+ T lymphocytes in SCID mice perorally infected with Encephalitozoon cuniculi

The role of antibodies in the immune response to microsporidiosis was studied using a novel anti-exospore monoclonal antibody (MAb) P5/H1, which recognizes surface antigens of Encephalitozoon cuniculi. The effect of the MAb on microsporidial infection in vivo was to prolong the survival of previously CD4+ reconstituted, perorally infected and intraperitoneally MAb-treated SCID mice. The MAb decreased the numbers of E. cuniculi spores in peritoneal smears obtained post mortem. These results suggest a possible role for antibodies in protection against perorally acquired E. cuniculi infection.

Humoral response of chicken infected with the microsporidium Encephalitozoon hellem

Chicken (Gallus gallus) were used as the experimental model for study of immune response against the microsporidium Encephalitozoon hellem (Didier et al., J Inf Dis 163:617-621, 1991) infection in birds. Two-day-old chicken were infected perorally or intraperitoneally with a dose of 10(7) spores of E. hellem. The anti-E. hellem immunoglobulin (Ig)A, IgY, and IgM antibody responses in sera and dropping sample extracts were determined by enzyme-linked immunosorbent assay. Results have shown specific antibody production in sera and intestinal secretions of infected birds. Chicken inoculated perorally developed the lowest antibody response. Microsporidian spores were not identified in the smears from cloacal swab samples of individual chicken. Intestinal segment cultures of perorally infected chicken cultivated in vitro showed the highest production of specific IgY and IgA antibodies in jejunum segments. In the further course of infection, the colon produced the highest amount of IgA, and the ileum and colon produced the highest amount of IgY.

Effects of a novel anti-exospore monoclonal antibody on microsporidial development in vitro

The possible role of humoral antibodies in the immune response to microsporidiosis was studied using a novel anti-exospore monoclonal antibody (MAb) P5/H1 which recognised Encephalitozoon cuniculi. The effect of the P5/H1 MAb on microsporidial growth in vitro resulted in a reduction of the numbers of E. cuniculi spores in a Vero E6 cell-line culture. This reduction in the number of infected cells and the decrease of intracellular spores in infected cells was found when MAb P5/H1 was present in cultures, compared to cultures with an irrelevant isotype control MAb. Moreover, the presence of P5/H1 MAb increased the number of phagocytosed spores in macrophage cultures, and increased the activation of macrophages measured by nitrite oxide production. These results suggest a possible partial role of specific humoral antibodies in the protection against E. cuniculi infection.