SCHISTOSOMA PARASITES EVOKE STRESS RESPONSES IN THEIR SNAIL HOST BY ACYTOKINE-LIKE FACTOR INTERFERING WITH NEUROENDOCRINE MECHANISMS

Results obtained with the model Trichobilharzia ocellata-Lymnaea stagn alis confirm the hypothesis that schistosome parasites evoke physiolog ical effects in their snail host-castration and giant growth-by interf ering with neuroendocrine systems (NES) regulating the physiological p rocesses concerned. In the haemolymph of the snail host a factor, call ed schistosomin, was found acting at both the central and the peripher al parts of NES involved in regulation of reproduction and growth. Sch istosomin appears to be a host-derived factor, probably released by ha emocytes and by cells in the connective tissue. It meets the criteria of being a cytokine-like factor, which accounts for its interference w ith NES. Furthermore, the physiological effects caused by schistosomes in the snail host resemble aspecific stress responses in mammals, e.g . upon a bacterial challenge.