RELATIONSHIP BETWEEN THE PATHOGENICITY OF SCHISTOSOMA-MANSONI IN MICEAND THE SUSCEPTIBILITY OF THE VECTOR MOLLUSK - IV - INFECTIOUSNESS OFTHE MIRACIDIA

Objective The infection ability of miracidia of BH and SJ strains of S . mansoni, obtained front mice infected with cercariae taken from Biom phalaria glabrata and Biomphalaria tenagophila, genetically selected f or susceptibility is compared with the infection ability of miracidia obtained from mice infected with larvae from non-selected mollusks. Ma terial and Method Progeny of S. mansoni resulting from successive infe ctions of selected mollusk sproduced various generations of selected m iracidia. Selecion of B. glabrata and B. tengophila was carried out by autofertilization of mollusks susceptible to the BH and SJ strains of S. mansoni. Five generations of mollusks (from parental down to F4), were used in the experiment. Tests for the infectiousness of the mirac idia used 10 larvae; susceptibility was checked starting on day 30 aft er infection, for 90 days, through observation for the presence of cer cariae. Results The results showed that susceptibility of the the sele cted mollusks in the face of the respective sympatric strains was not altered by the selection process of S. mansoni. However F4 miracidia o f the BH strain were more infectant for non-selected B. glabrata than parental miracidia of the same strain. Miracidia of BH and SJ strains, parental generation, and BH strain, F3 generation, showed the same in fectiousness in selected B. glabrata. Nevertheless, these mollusks had distinct infection rates from allopatric selected miracidia (SJ strai n, F4 generation). The generation of successive successive infections of S. mansoni SJ in selected B. tenagophila resulted in the adaptation of the worm strain to the species of mollusk. B. tenagophila was neve r susceptible to the BH strain, even when selected mollusks and tremat odes were employed. The susceptibility/infectiousness of the pair B. t enagophila-SJ S. mansoni strain was only changed by the selection proc ess of the mollusks. Conclusion As non-selected B. glabrata were more intensively-infected by selected BH miracidia than by non-selected BH miracidia, one is led to surmise that the greater pathogenicity of S. mansoni from susceptible mollusks implies the greater infection abilit y of these miracidia.