IMMUNODIAGNOSIS OF FASCIOLA-HEPATICA INFECTION (FASCIOLIASIS) IN A HUMAN-POPULATION IN THE BOLIVIAN ALTIPLANO USING PURIFIED CATHEPSIN-L CYSTEINE PROTEINASE

Cathepsin L1 (CL1), an immunogenic cysteine proteinase secreted by juv enile and adult Fasciola hepatica, was assessed for its potential as a diagnostic agent for the serologic detection of human fascioliasis. U sing ELISAs, we compared the ability of liver fluke homogenates (LFH), excretory/secretory (ES) products, and CL1 to discriminate between se ropositive (infected) and seronegative (noninfected) individuals withi n a population of 95 patients from the Bolivian Altiplano. A high prev alence of human fascioliasis has been reported in this region. The div ision between the seropositive and seronegative individuals was poorly defined when LFH was used as the antigen. A greater discrimination be tween these populations was achieved with both ES and CLI. A K-means c luster analysis using the combined ES and CL1 ELISA data identified a cluster of seropositive individuals. Cathepsin L1 detected a subset (2 0) of these seropositive individuals while ES detected all 26; however , ES detected nine additional individuals that were in the seronegativ e cluster. The ratio of the mean absorbance readings between seroposit ive and seronegative individuals was markedly improved by using conjug ated second antibodies to IgG4, the predominant isotype elicited by in fection. In these IgG4-ELISAs, CL1 again identified fewer individuals as seropositive than did ES, but improved the discrimination between t he seropositive and seronegative individuals and thus provided a more conclusive diagnosis. Sera obtained from patients infected with schist osomiasis mansoni, cysticercosis, hydatidosis, and Chagas' disease wer e negative in these assays, which demonstrated the specificity of the IgG4-ELISA for detecting fascioliasis, Twenty of the 95 patients (21%) were seropositive for fascioliasis by the CL1 IgG4-ELISA, confirming the earlier reports of the high prevalence of disease in this region. A standardized diagnostic test for human fascioliasis, based on an ELI SA that detects IgG4 responses to CL1, could be available to all diagn ostic centers if sufficient quantities of recombinant CLI can be produ ced.