Seasonal changes in the Plasmodium falciparum population in individuals and their relationship to clinical malaria: a longitudinal study in a Sudanese village
Residents of Daraweesh village in Sudan were monitored for Plasmodium falciparum infection and malaria morbidity in 3 malaria seasons from 1993 to 1996. Malaria parasites were detected microscopically and by polymerase chain reaction (PCR) in a series of cross-sectional surveys. PCR revealed submicroscopical infections during the dry season, particularly among individuals who had recovered from a malaria episode following successful drug treatment. Clinical and subclinical infections were contrasted by assaying for allelic polymorphism at 2 gene loci, MSP-1 and GLURP and 2 hypotheses examined with reference to these data: that clinical malaria is associated with infection with novel parasite genotypes not previously detected in that host, or alternatively, that clinical malaria episodes are associated with an increased number of clones in an infection. We detected more mixed infections among clinical isolates, but people carrying parasites during the dry season were not found to have an increased risk of disease in the following malaria season. There was a clear association of disease with the appearance of novel parasite genotypes.(Received July 28 1997)
(Revised January 12 1998)
(Accepted January 13 1998)
Key Words: Plasmodium falciparum; asymptomatic infection; PCR genotyping; longitudinal field studies; Sudan.
c1 Corresponding author: Department of Infectious and Tropical Disease, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK. Tel: +171 927 2331. Fax: +171 636 8739. E-mail: email@example.com
p1 Present address: Department of Infectious and Tropical Disease, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.