Impact of the age of Biomphalaria alexandrina snails on Schistosoma mansoni transmission: modulation of the genetic outcome and the internal defence system of the snail

Of the approximately 34 identified Biomphalariaspecies,Biomphalaria alexandrina represents theintermediate host of Schistosoma mansoni in Egypt. Usingparasitological and SOD1 enzyme assay, this study aimed to elucidate the impact ofthe age of B. alexandrina snails on their genetic variability andinternal defence against S. mansoni infection. Susceptible andresistant snails were reared individually for self-reproduction; four subgroups oftheir progeny were used in experiment. The young susceptible subgroup showed thehighest infection rate, the shortest pre-patent period, the highest total cercarialproduction, the highest mortality rate and the lowest SOD1 activity. Among the youngand adult susceptible subgroups, 8% and 26% were found to be resistant, indicatingthe inheritance of resistance alleles from parents. The adult resistant subgroup,however, contained only resistant snails and showed the highest enzyme activity. Thecomplex interaction between snail age, genetic background and internal defenceresulted in great variability in compatibility patterns, with the highest significantdifference between young susceptible and adult resistant snails. The resultsdemonstrate that resistance alleles function to a greater degree in adults, withhigher SOD1 activity and provide potential implications for Biomphalariacontrol. The identification of the most susceptible snail age enablesdetermination of the best timing for applying molluscicides. Moreover, adultresistant snails could be beneficial in biological snail control.