HETEROGENEITIES IN SCHISTOSOME TRANSMISSION DYNAMICS AND CONTROL

We review the theoretical framework for exploring the impact of indivi dual and spatial heterogeneities in patterns of exposure and contamina tion and on the basic reproduction number, R-0, for human schistosomes . Analysis of water contact data for 5 communities in Zimbabwe and Mal l suggests that the impact is substantial, increasing R-0 by factors o f up to 6.5, mostly due to highly overdispersed distributions of conta ct rates among individuals. Several practical conclusions emerge: conc entration of contacts at a single site should be avoided; the impact o f control targeted at certain sites cannot be predicted without knowle dge of how individuals' contacts are distributed among sites; control programmes targeted at individuals or sites contributing most to trans mission can be very efficient but, conversely, will be ineffective if any of these individuals or sites are missed.