Relation between Plasmodium falciparum asymptomatic infection and malaria attacks in a cohort of Senegalese children.
BACKGROUND
It is important to establish whether or not the presence of malaria parasites in peripheral blood of asymptomatic individuals is a predictor of future clinical mild malaria attacks (MMA). The aim of this study was to determine how an asymptomatic positive thick blood smear could be related to the occurrence of a MMA during the nine following days.


METHODS
The study was conducted in a cohort of 569 Senegalese children, who were investigated for Plasmodium falciparum asymptomatic carriage at two different times of the transmission season, the beginning (September) and the end (November). The occurrence of MMA was investigated in asymptomatic carriers and non-carriers, every three days for nine consecutive days. Survival analysis was performed and risk estimates were calculated by Cox proportional hazards model.


RESULTS
At the beginning of the transmission season, 27.8% (147/529) of the children were asymptomatic carriers (ACs) and 5.4% (8/147) of MMA occurred among these, versus 1% (4/382) among non-carriers (RR = 5.32; IC = [1.56-18.15], p = 0.008). At the end of the transmission season, the frequency of asymptomatic carriers was similar to that observed at the beginning of the season (31.9%, p = 0.15), but no MMA was detected during this period.


CONCLUSIONS
A significant association between P. falciparum asymptomatic carriage and the occurrence of MMA at the beginning of the transmission season was demonstrated, with a five-fold increase in the risk of developing a MMA in ACs. In the context of a possible distribution of IPTc in the future, drug strategies may have dramatic consequences due to the existence of ACs (both long term and short term), as they seem to play an important role in the individual protection to malaria, in the most exposed age groups.
Le Port
Agnès
A
Institut de Recherche pour le Développement (IRD), Unité de Recherche 010: Santé de la mère et de l'enfant en milieu tropical, Laboratoire de Parasitologie, Faculté de Pharmacie, 4 avenue de l'Observatoire, 75006 Paris, France. agnes.leport@ird.fr
Cot
Michel
M
Etard
Jean-François
JF
Gaye
Oumar
O
Migot-Nabias
Florence
F
Garcia
André
A
D000293:Adolescent; D000818:Animals; D001769:Blood / Q000469:parasitology; D002353:Carrier State / Q000453:epidemiology / Q000469:parasitology*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D006801:Humans; D008288:Malaria / Q000453:epidemiology / Q000469:parasitology* / Q000503:physiopathology*; D010963:Plasmodium falciparum / Q000302:isolation & purification*; D012307:Risk Factors; D012621:Seasons; D012675:Senegal / Q000453:epidemiology