Use of 75Se tracer and autoradiographic techniques in the study of schistosomiasis.

The paper provides an overview of recent studies on the use of 75Se to tag larval schistosomes and to monitor their migration and distribution patterns in naive mice and those previously exposed to cercariae. The principles and techniques of radioassay and autoradiography in studying various aspects of 75Se-labelled larval schistosomes are described. The main shortcoming of radioassay in monitoring location and movement of labelled schistosomula is that some of the label dissociates from the schistosomula and accumulates in host tissues, notably the liver. Dissociated label is indistinguishable from schistosomula-bound label making monitoring of parasite migration extremely difficult. This difficulty is overcome by compressed tissue autoradiography where labelled schistosomula can be seen as reduced silver foci on an autoradiographic film, whereas dissociated label is too diffusely distributed to produce such reduced silver foci. Furthermore, using autoradiography, quantitative information on parasite migration in normal and immunized laboratory animals can be obtained that would be impossible using traditional recovery techniques. In addition to using 75Se tracer in migration studies, the radio-isotope has potential for elucidating various aspects of schistosome transmission ecology and snail population dynamics in natural waters.