POTENTIAL OF A RECOMBINANT SCHISTOSOMA BOVIS-DERIVED GLUTATHIONE-S-TRANSFERASE TO PROTECT CATTLE AGAINST EXPERIMENTAL AND NATURAL SCHISTOSOMA-MATTHEEI INFECTION

The potential of a recombinant Schistosoma bovis-derived glutathione S -transferase (rSb28GST) to protect cattle against S. mattheei infectio n was tested in Zambia. All animals were challenged 2 weeks after the second inoculation with either 0.250 mg rSb28GST in adjuvants (vaccina ted calves, n = 14) or adjuvants alone (controls, n = 14). In a first experiment, 7 vaccinated and 7 control animals were exposed to 10 000 S. mattheei cercariae percutaneously. All animals developed clinical s chistosomiasis 7-8 weeks after challenge. At perfusion, 12 weeks after challenge, vaccinated and control groups had averages of 887 and 541 eggs per gramme (epg) faeces, 6515 and 5990 worms, and 4.2 and 3.4 mil lion tissue eggs, respectively. These results indicate that the immuni zation protocol used did not protect these calves against the massive single experimental challenge. In a second experiment, another 2 group s (n = 7) of vaccinated and control animals were challenged naturally over a period of 9 months on a farm known to be endemic for S. matthee i. The natural infections were much lighter in intensity, as indicated by the mean faecal egg count (13 epg), worm count (139) and tissue eg g count (294 000) in non-vaccinated controls. In vaccinated calves, si gnificant reductions in female worm burdens (50%), faecal egg counts ( 89%) and miracidial counts (93%) were recorded. Total tissue egg count s were also reduced by 42% in vaccinated animals. It therefore appears that the rSb28GST can provide significant protection in cattle agains t S. mattheei under conditions of low to moderate natural infection.