Evidence for widespread occurrence of antibodies to Encephalitozoon cuniculi (Microspora) in man provided by ELISA and other serological tests.

The enzyme-linked immunosorbent assay (ELISA) was used to survey human sera for antibodies to Encephalitozoon cuniculi using spores obtained from in vitro cultures as antigen. Sera were obtained from patients with tropical diseases, neurological and renal disorders, patients who were HIV positive and those who had been tested for HIV but found to be negative. Sera from inhabitants of the village of Jali, The Gambia and from healthy blood donors were also examined. Numerous sera from all groups except the blood donors gave positive ELISA reactions at dilutions of 1:400. On titration, those with titres of 1:400 were reclassified as negative. Antibody titres of 1:800 and above were considered to be indicative of past or present infections with E. cuniculi. Many of these ELISA seropositives were also positive by IFAT or PAP. When examined by Western blotting of SDS-PAGE protein profiles of E. cuniculi spores, sera from many patients who had a tropical association reacted with the characteristic profiles shown by known positive mouse and rabbit sera. Others in the tropical group showed antibody binding to some but not all of the immunodominant polypeptides and yet others were negative in spite of their reactivity in the ELISA, IFAT or PAP test. Less agreement between ELISA and Western blotting results was obtained with the other groups of patients, although reactivity with one or more of the major polypeptide bands was sometimes seen. Serum from one blood donor, examined by ELISA and Western blotting, was positive. Differences in the methods of antigen preparation and of epitopes recognized by individuals may account for different reactivities in the tests. It is concluded that infections of E. cuniculi are common in the tropics and that reactivations of these infections might be a hazard to AIDS patients.