Chemoattraction of Ichthyophthirius multifiliis (Ciliophora) theronts to host molecules

Mechanisms in the host-finding process of Ichthyophthirius multifiliis were studied in vitro by a novel bioassay using 24-well multidishes supplied with bottom layers of agar with chemoattractants. It was shown that low molecular weight molecules (carbohydrates, amino acids, fatty acids, urea) did not attract theronts. In contrast, sera and mucus from a range of teleosts (including marine fish) were effective attractants. Fractionation by gel filtration of fish serum allowed determination of the molecular size of the attracting proteins. Further biochemical studies suggested the chemoattractants to be present in fractions with host immunoglobulin and some still undetermined proteins. No clear association between enzyme activity and chemotactic potential was seen. The high chemoattractive effect of serum from various unrelated teleosts corresponds to the low host specificity of I. multifiliis and suggests that serum factors in mucus could be involved in host finding of the parasite. Society for Parasitology Inc.