Table 2.

Why is Mass Drug Administration (or Preventive Chemotherapy) not sufficient to eliminate schistosomiasis transmission by itself?

•	100% MDA Coverage is very hard to achieve—and will only get more difficult as prevalence and intensities approach zero
•	Praziquantel does not kill juvenile worms—which then grow up to be adults
•	Production of enough praziquantel is a challenge—if we really treat everyone who is infected
•	There may be a prevalence at which it is not longer cost-effective to keep doing MDA
•	There may be a prevalence at which it is no longer acceptable to the population to undergo MDA
•	Reinfection of treated people can continue to occur if infected snails remain in the environment
•	The multiplicative phase of the life cycle is in the snail host (vector)
•	If poor sanitation, vector snails and a few infected people remain—transmission will continue unless a “break point” in one of these parameters is achieved—but we do not know what that “break point” is.