SUPPRESSION OF SCHISTOSOMA-BOVIS EGG-PRODUCTION IN CATTLE BY VACCINATION WITH EITHER GLUTATHIONE-S-TRANSFERASE OR KEYHOLE LIMPET HEMOCYANIN

Two of the antigens which have shown vaccine potential in animal exper iments against Schistosoma mansoni are glutathione-S-transferase (GST) and GP38, protective epitopes of which are shared with keyhole limpet haemocyanin (KLH). We therefore tested S. bovis GST and KLH for vacci ne efficacy against S. bovis in the natural Zebu cattle host. In a pre liminary experiment three vaccinations with a total of 1.39 mg of nati ve GSTs of S. bovis induced specific antibody at the time of challenge as detected by Western blotting and ELISA and mean faecal egg counts between weeks 6-10 post-challenge were reduced by 56.4 to 82.5% compar ed to non-vaccinated controls. Mean adult worm recoveries and tissue e gg densities in large intestine and liver samples were also reduced in the vaccinated group, but these differences were not statistically si gnificant. In a subsequent experiment one group of calves was vaccinat ed with a similar schedule to that used above; a second group of calve s was given only two injections of GST (total 0.48 mg protein); a thir d group of calves was vaccinated twice with a total of 2.0 mg KLH in P BS. All three vaccination schedules induced specific antibody. Both GS T vaccination schedules induced significant reductions in faecal egg c ounts compared to non-vaccinated controls and in this experiment tissu e egg densities were also significantly reduced. A striking finding, h owever, was that adult worm counts were not reduced by vaccination. An essentially similar outcome resulted from KLH vaccination, since ther e were significant reductions in faecal and tissue egg counts in the a bsence of a reduction in adult worm numbers. This type of immunity mim ics that induced by natural or experimental infections in the calf and clearly has implications for vaccine design.