Immunoassays as an auxiliary tool for the serodiagnosis of Schistosoma mansoni infection in individuals with low intensity of egg elimination.

In an attempt to improve the screening of Schistosoma mansoni-infected individuals from a low-transmission area, we established a protocol that includes three independent coproscopy examinations and two serological assays. Three stool samples were examined using the Kato-Katz and free sedimentation methods and serum samples were tested by IgG-ELISA and IgM-immunofluorescence. Two hundred and sixty-nine individuals participated in the survey: 132 individuals (49%) showed positive serological test results. Of these, 16 (6%) had positive results in stool examination in the first sample batch. However, there were also cases with positive serological test results in spite of negative Kato-Katz stool examinations. Additional stool samples were obtained from these subjects and in this way an additional 11 egg-excretors were found. Our findings suggest that a screening method that combines antibody isotype detection and repeated parasitological stool examinations could increase the chances of detecting S. mansoni-infected patients.