Analysis of factors associating to parasitism and vaccine development of re-emerging Parasite, Echinococcus, using the alternative definitive host model

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To improve the alternative definitive host model for Echinococcus multilocularis, different kinds of steroids, and different doses, sites, periods and frequencies of administration were compared using Mongolian gerbils. The most worms with less side effect were recovered by the following combination; steroid : prednisolone tertiary-butylacetate (PTBA), dose: 5mg/head, site: subcutaneous, period: from 1 week before infection to the end of the experiment, frequency: every other day. Strain comparison of gerbils indicated more worms were recovered from the gerbils raised in our laboratory than commercially available two inbred strains. In hamster, CN inbred strain harbored more worms than CAN strain.Functional immunity against the establishment of the parasites could not be specified. Adiministration of cyclosporin A or different blockers of arachidonic cascade did not improve the worm recovery from the model animals as that of PTBA did. Nor, improvement of worm recovery was not achieved by using mast cell deficient W/WィイD1vィエD1 mice.The model could be successufully applied to E, vogeli. In this model, the parasite eggs was excreted form gerbils at 35 days post infection (DPI) and mature parasites were recovered at 50 DPI.To analyze protective immunity against adult E. multilocularis in hamsters, re-infection and oral immunization studies were carried out. Worm recovery after challenge infection was significantly reduced in the re-infection groups but not in the oral immunization groups. In the reinfection groups, increase of specific serum IgG, IgA and intestinal IgA secretion was observed, however, in the oral immunization groups, only serum IgG increased. These results indicated that acquired resistance against adult E.multilocularis may be associated with systematic and local recognition of the parasite antigen, especially in IgA reaction.