Detection by enzyme immunoassay of serum immunoglobulin G antibodies that recognize specific Cryptosporidium parvum antigens

Human infection with Cryptosporidium parvum usually elicits characteristic immunoglobulin G (IgG), IgA, and IgM antibody responses against two sporozo ite surface antigens,vith apparent molecular masses of approximately 27 and 17 kDa. We have determined that these two antigens are actually complex: f amilies of related antigens, We have developed two new enzyme-linked immuno sorbent assays (ELISAs) for the detection and quantitation of serum IgG ant ibodies against both antigens. The assays utilize a recombinant form of the 27-kDa antigen and a partially purified native fraction isolated from soni cated whole oocysts that contains 17-kDa antigen. An immunoblot assay previ ously developed in our laboratory sen ed as the reference, or "gold standar d" seroassay for the assessment of the new ELISAs. Positive responses with the recombinant-27-kDa-antigen ELISA were correlated with the immunoblot re sults for the 27-kDa antigen, with a sensitivity and specificity of 90 and 92%, respectively. Similarly, positive responses with the partially purifie d native-17-kDa-antigen ELISA correlated with the immunoblot results for th e 17-kDa antigen, with a sensitivity and specificity of 90 and 94%, respect ively. For both ELISAs the median IgG antibody levels for serum sets collec ted during outbreaks of waterborne C. parvum infection were at least 2.5-fo ld higher than the levels determined for a nonoutbreak set. Using the immun oblot as the "gold standard," the new ELISAs were more specific and, in the case of the 27-kDa-antigen ELISA, more sensitive than the crude oocyst ant igen ELISA currently in use. These assays will be useful in future epidemio logic studies.