Schistosoma Parasites Evoke Stress Responses in Their Snail Host By a Cytokine-Like Factor Interfering With Neuro-Endocrine Mechanisms

Results obtained with the model Trichobilharzia ocellata-Lymnaea stagnalis confirm the hypothesis that schistosome parasites evoke physiological effects in their snail host-castration and giant growth-by interfering with neuroendocrine systems (NES) regulating the physiological processes concerned. In the haemolymph of the snail host a factor, called schistosomin, was found acting at both the central and the peripheral parts of NES involved in regulation of reproduction and growth. Schistosomin appears to be a host-derived factor, probably released by haemocytes and by cells in the connective tissue. It meets the criteria of being a cytokine-like factor, which accounts for its interference with NES. Furthermore, the physiological effects caused by schistosomes in the snail host resemble aspecific stress responses in mammals, e.g. upon a bacterial challenge.