Application of immunoassay methods in the serodiagnosis of human filariasis

To be more definitive as a serodiagnostic method, an ideal immunoassay for detection of filaria-specific antibody and filarial antigens in body fluids should identify active filarial infection and differentiate between past and present infection. It should perform well in the areas of precision, reproducibility, parallelism, and sensitivity and should use reference and quality control reagents prepared with human body fluids that contain defined amounts of filarial antigen. Moreover, a sufficient quantity of reference serum in stable form should be made available to permit interlaboratory cross-standardization. Difficulty with uniform radio labeling of filarial antigen extracts and the interference of human antibody have combined to eliminate the competitive-binding immunoassay as a useful method. Of the noncompetitive methods evaluated, the immunoradiometric assay (IRMA) and its nonisotopic counterpart, the immunoenzymetric assay (IEMA), perform best. As a factor masking diagnostically important antigenic determinants, the variable amount of human antibody in blood interfered with all assay designs tested. Better characterization of the antigen(s) circulating in the blood or excreted into the urine of infected individuals will improve assay specificity and sensitivity and will facilitate the preparation of antibody probes more specifically targeted to filarial antigens for use in both the IRMA and IEMA.