Use of the Falcon™ Assay Screening Test-Enzyme-Linked Immunosorbent Assay (FAST-ELISA) and the Enzyme-Linked Immunoelectrotransfer Blot (EITB) to Determine the Prevalence of Human Fascioliasis in the Bolivian Altiplano
Laboratory of Parasite Immunology and Pathology, Department of Pathology, University of Puerto Rico School of Medicine, Danchurchaid, Instituto Nacional de Laboratorios de Salud, Ministerio de Prevision Social y Salud Publica, Parasitic Diseases Branch, Division of Parasitic Diseases, Center for Infectious Diseases, Centers for Disease Control, San Juan, Puerto Rico
A collaborative study between the University of Puerto Rico School of Medicine, the Centers for Disease Control, the Bolivian Ministry of Health, and private voluntary organizations (Foster Parents Plan International and Danchurchaid) working in Bolivia has identified a region in the northwestern Altiplano of Bolivia near Lake Titicaca as harboring the highest prevalence of human fascioliasis in the world reported to date. Two serologic techniques (the Falcon™ assay screening test-enzyme-linked immunosorbent assay [FAST-ELISA] and the enzyme-linked immunoelectrotranfer blot [EITB]) were used in the determination of its prevalence. One hundred serum samples and 73 stool samples were obtained from Aymara Indians from Corapata, Bolivia. Antibody absorbance levels to Fasciola hepatica excretion-secretion antigens were compared with EITB banding patterns using the same antigen preparation. A positive FAST-ELISA result was defined as an absorbance value greater than the mean plus three standard deviations of two sets of normal negative controls (Puerto Rican and Bolivian). Using this criterion, 53 of 100 sera tested were found positive by this technique. Within this group, 19 (95%) of 20 individuals who were parasite positive were also positive by FAST-ELISA. An additional 24 individuals who were negative for F. hepatica eggs and 10 individuals for whom no specimens were received were also positive by FAST-ELISA. Among the 53 individuals negative for F. hepatica eggs, 29 were also negative by FAST-ELISA. The EITB analysis of the sera from confirmed infected individuals revealed at least three F. hepatica (Fh) bands with molecular weights of 12, 17, and 63 kD, respectively. All 20 sera from infected individuals recognized the Fh12 band; the Fh17 and Fh63 bands were only observed in those individuals with the highest FAST-ELISA absorbances, which suggests that they may be markers for acute infection, in which antibody levels tend to be high. Additional serum samples from six individuals that were negative by coprology and FAST-ELISA did not recognize any of the above markers. Using EITB, 42 (79%) of the 53 persons who were positive by FAST-ELISA were confirmed. These studies support the use of immunologic techniques in the determination of prevalence in epidemiologic studies of human fascioliasis.