Parasitology



Heterogeneities in schistosome transmission dynamics and control


M. E. J. WOOLHOUSE a1c1, J.-F. ETARD a2, K. DIETZ a3, P. D. NDHLOVU a4 and S. K. CHANDIWANA a4
a1 Centre for Tropical Veterinary Medicine, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG
a2 L'Institut Francais de Researche Scientifique pour le Developpement en Cooperation (ORSTOM), BP1386, Dakar, Senegal
a3 Institut für Medizinische Biometrie, Westbahnhofstrasse 55, D72070 Tübingen, Germany
a4 Blair Research Laboratory, PO Box CY573, Causeway, Harare, Zimbabwe

Abstract

We review the theoretical framework for exploring the impact of individual and spatial heterogeneities in patterns of exposure and contamination and on the basic reproduction number, R0, for human schistosomes. Analysis of water contact data for 5 communities in Zimbabwe and Mali suggests that the impact is substantial, increasing R0 by factors of up to 6·5, mostly due to highly overdispersed distributions of contact rates among individuals. Several practical conclusions emerge: concentration of contacts at a single site should be avoided; the impact of control targeted at certain sites cannot be predicted without knowledge of how individuals' contacts are distributed among sites; control programmes targeted at individuals or sites contributing most to transmission can be very efficient but, conversely, will be ineffective if any of these individuals or sites are missed.

(Received February 14 1998)
(Revised May 22 1998)
(Accepted May 22 1998)


Key Words: basic reproduction number; exposure; heterogeneity; schistosomiasis; water contact.

Correspondence:
c1 Corresponding author: Centre for Tropical Veterinary Medicine, University of Edinburgh, Easter Bush, Roslin, Midlothian EH29 9RG. Tel: +0131 650 6216. Fax. +0131 650 6289. E-mail: mark.woolhouse@ed.ac.uk


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