The serological differentiation of acute and chronic Schistosoma japonicum infection by ELISA using keyhole limpet haemocyanin as antigen

Abstract

Antibodies (immunoglobulin (Ig) G and IgM) that recognize keyhole limpet haemocyanin (KLH), which shares a well defined carbohydrate epitope with the surface of larval schistosomes, were determined by enzyme-linked immunosorbent assay in patients with acute or chronic schistosomiasis japonica. Marked differences in IgG and IgM responses were evident between acute and chronically infected patients at a serum dilution of up to 1:2000. The acute sera had mean (±standard deviation) optical density values at 405 nm for IgG and IgM of 0.64±0.18 and 0.30±0.19 respectively; the chronic sera had mean readings for IgG and IgM of 0.14 ± 0.08 and 0.04 ± 0.03 respectively. Setting the lowest positive limit at 2 standard deviations above the mean value for chronic sera, 41 (98%) of the 42 patients previously diagnosed as having acute schistosomiasis were correctly identified by anti-KLH IgG and 35 (83%) of the 42 patients were correctly identified by anti-KLH IgM detection. Of 17 patients studied longitudinally, IgG optical density values dropped 45% and those of 5 patients fell below the established cut-off level 6 months after treatment. This study supports the use of KLH for rapidly and easily identifying individuals with acute Schistosoma japonicum infection.