COMPARISON OF THE PROTECTIVE EFFICACY ON MEKONGI SCHISTOSOMIASIS IN MICE INDUCED BY ANTIGENS DERIVED FROM CERCARIAE, SCHISTOSOMULAE AND ADULT WORMS

Protective efficacy of the extracts of cercariae, schistosomulae and a dult worms of S. mekongi was studied in mice receiving immunizations w ith these extracts emulsified with Freund's complete adjuvant initiall y and incomplete adjuvant subsequently, and compared with mice receivi ng physiological saline with or without adjuvants as controls. After c hallenge with cercariae, the animals were sacrificed and the larvae or adult worms harvested by lung recovery and perfusion techniques on da y 5 and weeks 6-8, respectively. Worm reduction rates were significant ly higher in mice receiving extracts of schistosomula (59%) and adult worms (51 %) than in those receiving the cercarial extracts (31%). Sim ilar findings were obtained with the perfusion technique showing worm reduction rates of 57%, 53% and 30% in mice receiving extracts of schi stosomulae, adult worms and cercariae, respectively. ELISA antibody ti ters were correspondingly increased in mice receiving extracts of schi stosomulae and adult worms, but not in those receiving cercariae. This apparent association may be inadequate to suggest that the increase i n ELISA titer be used as an indicator for resistance in mekongi schist osomiasis.