An investigation of the interactions of some factors influencing the infectivity of Schistosoma mansoni miracidia to Biomphalaria glabrata

Sturrock R. F. and Upatham E. S. 1973. An investigation of the interactions of some factors influencing the infectivity of Schistosoma mansoni miracidia to Biomphalaria glabrata. International Journal for Parasitology3: 35–41. A 3³ replicated factorial experiment showed that there were significant first-order interactions between the effects of turbidity, salinity and pH on the infectivity of Schistosoma mansoni miracidia to Biomphalaria glabrata. The main factor effects resembled those obtained when the factors were studied individually. There was a negative regression of infection rate on the logarithm of the level of both turbidity and salinity, and a curvilinear regression on pH, with a peak between 7 and 8. However, as the main factors only accounted for little over half of the observed variance, the interactions are extremely important and greatly reduce the chance of a miracidium infecting a snail. These findings are relevant to natural transmission sites in endemic areas and also suggest that quite minor variations in other factors may enhance the adverse effect of increased salinity on transmission in estuaries, and thus minimize the importance of such areas in the epidemiology of the parasite.