Schistosome cercariae of the genus
Trichobilharzia are the causative agent of
swimmers' itch. In order to characterize the
changes in parasites during and after the penetration of the
host skin, in vitro and in vivo (in
ducks and mice) transformations of T. szidati
cercariae to schistosomula were performed. Ultrastructural
observation revealed that cercariae
possess a simple outer tegumental membrane with a thick
glycocalyx. As with human schistosomes, the latter structure
disappears during transformation and a new double membrane
with putative protective function is formed. Our biochemical
and immunological observations showed that the carbohydrate-rich
glycocalyx of cercariae is readily bound by
lectins and antibodies. The in vitro transformation
to schistosomula can be detected by enhanced reactivity of 2 lectin
probes (PNA and ConA) with the surface. The
in vivo-transformed (skin and lung) schistosomula
appear to have few
surface ligands for the 12 lectin probes being tested.
Similarly, the cercarial surface and its remnants on the
in vitro-produced schistosomula is recognized by sera
from immunized mice and humans with cercarial dermatitis;
the tissue schistosomula fail to react with these antibodies.
The loss of surface targets as a part of parasite immune
evasion within the host is discussed.