Age and seasonal variation in the transition rates and detectability of Plasmodium falciparum malaria
The effect of acquired immunity on the duration of Plasmodium falciparum infections is unclear, although this is an important term in models of malaria transmission. It is problematical to determine the duration of infections because of the difficulty of distinguishing persisting infections from new ones, and because parasite densities are often transiently below the limit of detection. We recently developed a dynamic model for infection incidence, clearance and detection of multiple genotype P. falciparum infections and fitted it to a panel dataset from a longitudinal study in Northern Ghana. We now extend this model to allow for seasonal and age variation in infection rates and also age dependence in clearance and in detectability of infections. These models indicate that there is seasonal variation in the infection rate, and age dependence in detectability. The best fitting models had no age dependence in infection or clearance rates, suggesting that acquired immunity mainly affects detectability.(Received May 2 2005)
(Revised June 20 2005)
(Accepted June 20 2005)
(September 13 2005)
Key Words: Plasmodium falciparum; infection rate; clearance rate; detectability; seasonal variation; acquired immunity; model.
c1 Department of Public Health and Epidemiology, Swiss Tropical Institute, Socinstrasse 57, Postfach CH-4002, Basel, Switzerland. Tel: +41 (0) 61 284 82 82. Fax: +41 (0) 61 284 81 05. E-mail: Wilson.Sama@unibas.ch