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We describe a statistical model for the relationship between asexual parasite densities of Plasmodium falciparum and the infectivity of the host to mosquitoes. The model takes into account the delay between asexual parasitemia and infectivity resulting from the time course of gametocytemia. It also allows for the need for the blood meal to contain gametocytes of both sexes if infection is to take place. We show that by fitting this model to data from malariatherapy patients it can explain observed patterns of infectiousness of the human host and is consistent with distributions of gametocyte densities in malariatherapy patients. By integrating this model into an individual-based simulation of human populations exposed to endemic P. falciparum transmission, we are able to predict the contributions of different host age groups to the infectious reservoir. Comparison of model predictions with published estimates of this quantity confirms that infected adults hosts are likely to make a significant contribution to the reservoir of transmission, and points to the need for improved population-based estimates of this age-dependence in infectivity of humans in endemic areas.
Received September 18, 2005. Accepted for publication November 5, 2005.
Acknowledgments: We thank Professor Klaus Dietz and Dr. Louis Molineaux for comments on an earlier draft of this paper. We also thank the members of the Technical Advisory Group (Michael Alpers, Paul Coleman, David Evans, Brian Greenwood, Carol Levin, Kevin Marsh, F. Ellis McKenzie, Mark Miller, and Brian Sharp), the Project Management Team at the Program for Appropriate Technology in Health (PATH) Malaria Vaccine Initiative, and GlaxoSmith-Kline Biologicals S.A. for their assistance. We gratefully acknowledge the provision of the malariatherapy data from the United States Public Health Service through Bill Collins and Geoffrey Jeffery.
Financial support: The mathematical modeling study was supported by the PATH Malaria Vaccine Initiative and GlaxoSmithKline Biologicals S.A.
Disclaimer: Publication of this report and the contents hereof do not necessarily reflect the endorsement, opinion, or viewpoints of the PATH Malaria Vaccine Initiative or GlaxoSmithKline Biologicals S.A.
* Address correspondence to Amanda Ross, Swiss Tropical Institute, Socinstrasse 57, Postfach, 4002 Basel, Switzerland. E-mail: amanda.ross{at}unibas.ch
Authors’ addresses: Amanda Ross and Thomas Smith, Swiss Tropical Institute, Socinstrasse 57, PO Box, CH-4002, Basel, Switzerland, Telephone: 41-61-284- 8273, Fax: 41-61-284-8105, E-mails: amanda.ross{at}unibas.ch and Thomas-A.Smith{at}unibas.ch. Gerry Killeen, Ifakara Health Research and Development Center, PO Box 53, Ifakara, Kilombero District, Tanzania, Telephone: 255-748-477-118, Fax: 255-23-262-5312, E-mail: gkilleen{at}ihrdc.or.tz.
Reprint requests: Amanda Ross, Swiss Tropical Institute, Socinstrasse 57, PO Box, CH-4002, Basel, Switzerland.
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