Long-Term Asymptomatic Carriage of Plasmodium falciparum Protects from Malaria Attacks: a Prospective Study among Senegalese Children

S. Males, O. Gaye, A. Garcia
2008 Clinical Infectious Diseases  
Background. In areas of seasonal malaria transmission, long-term asymptomatic carriage of Plasmodium falciparum throughout the dry season has been primarily studied in terms of the parasites, and the clinical consequences of persistent parasite carriage are unknown. Methods. A prospective study was conducted in Senegal, from 2001 through 2003 among 1356 children living in areas where malaria is endemic, with seasonal transmission occurring from August through December. Crosssectional
more » ... ectional parasitological measurements and detection of active malaria attacks were performed. A malaria attack was defined as an axillary temperature у37.5ЊC, associated with a parasite density 12500 trophozoites/mL. Children harboring P. falciparum in June who did not have clinical signs were defined as asymptomatic carriers. The association of asymptomatic carriage with parasite densities and with the occurrence of malaria attacks during the rainy season were analyzed separately for the years 2002 and 2003, taking into account potential confounding covariates and use of antimalarial drugs. Results. The prevalence of asymptomatic carriage was 32% (332 of 1025 persons) in June 2002 and 23% (208 of 912 persons) in June 2003. Asymptomatic P. falciparum carriers had a significantly higher mean parasite density and a significantly lower probability of developing a malaria attack during the subsequent rainy season than did noncarriers (adjusted odds ratio in 2002, 0.56; ; adjusted odds ratio in 2003, 0.50; ). P p .01 P p .01 Conclusions. These results suggest that in areas of seasonal transmission, asymptomatic carriage of P. falciparum may protect against clinical malaria. Further studies are needed to understand the immune effectors and host susceptibility that could be involved in this phenomenon. Malaria is a major cause of illness and death in children in Africa [1]. In areas of seasonal transmission, outbreaks of Plasmodium falciparum malaria occur after the beginning of the rainy season, whereas, during the dry season, reports of clinical cases are rare. However, long-term asymptomatic carriers of P. falciparum can be found in the population throughout the dry season, despite a very low level of transmission [2] [3] [4] [5] . Longterm parasite carriage can be considered to be critical for parasite survival, because the infected individuals may constitute a major reservoir in the absence of trans-
doi:10.1086/526529 pmid:18199040 fatcat:fi5x26rluff5nd2hkvwdt5vlwe