CERCARIA-SCHISTOSOMULUM SURFACE TRANSFORMATION OF TRICHOBILHARZIA-SZIDATI AND ITS PUTATIVE IMMUNOLOGICAL IMPACT

Schistosome cercariae of the genus Trichobilharzia are the causative a gent of swimmers' itch. In order to characterize the changes in parasi tes during and after the penetration of the host skin, in vitro and in vivo (in ducks and mice) transformations of T. szidati cercariae to s chistosomula were performed. Ultrastructural observation revealed that cercariae possess a simple outer tegumental membrane with a thick gly cocalyx. As with human schistosomes, the latter structure disappears d uring transformation and a new double membrane with putative protectiv e function is formed. Our biochemical and immunological observations s howed that the carbohydrate-rich glycocalyx of cercariae is readily bo und by lectins and antibodies. The in vitro transformation to schistos omula can be detected by enhanced reactivity of 2 lectin probes (PNA a nd ConA) with the surface. The in vivo-transformed (skin and lung) sch istosomula appear to have few surface ligands for the 12 lectin probes being tested. Similarly, the cercarial surface and its remnants on th e in vitro-produced schistosomula is recognized by sera from immunized mice and humans with cercarial dermatitis; the tissue schistosomula f ail to react with these antibodies. The loss of surface targets as a p art of parasite immune evasion within the host is discussed.