Schistosoma haematobium in a Gambian community. IV. Antibody levels and change in egg output.

The indirect fluorescent antibody (FAT) and indirect haemagglutination (IHA) tests were used to study the serological response to Schistosoma haematobium in a Gambian community. The FAT was frequently positive in very young children and also in adults, in whom urine examination did not show ova. This was much less often the case with the IHA although this test sometimes gave negative results in heavily infected children. Examination of paired sera taken at six month intervals apart showed that titres changed in some subjects and that overall there was a slight change in antibody level. Correlation of antibody level with subsequent changes in egg output showed that high titres were associated with a tendency for the egg output to fall. This effect was most obvious over a period of 16 months' follow up and was not explicable solely in terms of a coincidental relationship with age or intensity of infection. It is suggested that serological parameters may have some relation to protective immunity and that the immune response must be considered as a factor in the epidemiology of the infection.