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  • Center for Disease Control Public Health Service Department of Health, Education, and Welfare, Atlanta, Georgia 30333

27 November 1979

To the Editor:

In my Presidential Address, when I was discussing the control of schistosomiasis by drugs, I stated: “The control of schistosomiasis by mollusciciding, however, has proven to be essentially ineffective.” Doctors Christie, Prentice, and Barnish took exception to this remark because I did not qualify my statement. In their letter they list some of the reasons why mollusciciding has been ineffective—because of use “in a haphazard manner, with inadequate precontrol studies” and “without proper knowledge” with regard to application, etc. In addition to these technical aspects, there are other reasons why the control of snail populations by mollusciciding is so difficult. Snail populations can be and have been drastically reduced by the application of chemicals in an endemic area. However, as soon as the program is terminated or relaxed for financial, logistic, or political reasons, the snail population usually returns to what it was before the chemicals were applied. There can he no short-term control of schistosomiasis by the use of molluscicides.