Before commenting on technical aspects of Dr. Olivier's paper, I would like to emphasize some points made in the Introduction. In view of our mutual experiences, two concepts need especially to be stressed: (1) that schistosomiasis is spreading rapidly; and (2) that there is an urgent need for obtaining better knowledge of the biology (in its broadest sense) of the vector snails.
With regard to the spread of schistosomiasis, three countries in another part of the world (Egypt, Sudan, and Iraq) will be mentioned. It is important to note that in Egypt more than half of the population, or an estimated 15 million people, have intestinal or vesicular schistosomiasis or both. Under present conditions of sanitation, education and medical treatment, the only hope of alleviating this serious situation lies in the control of the vector snails. It must be remembered that Egypt is overpopulated and in order to feed the growing population the country is forced to bring more and more of the Nile Valley into perennial irrigation.