Submicroscopic Plasmodium falciparum gametocyte carriage is common in an area of low and seasonal transmission in Tanzania

OBJECTIVE: Recently developed molecular gametocyte detection techniques have shown that submicroscopic Plasmodium falciparum gametocytes are common in symptomatic patients and can infect mosquitoes. The relevance for the infectious reservoir of malaria in the general population remains unknown. In this study, we investigated submicroscopic asexual parasitaemia and gametocytaemia in inhabitants of an area of hypoendemic and seasonal malaria in Tanzania. METHODS: Two cross-sectional malariometric surveys were conducted in the dry and wet seasons of 2005 in villages in lower Moshi, Tanzania. Finger prick blood samples were taken to determine the prevalence of P. falciparum parasites by microscopy, rapid diagnostic test and real-time nucleic acid sequence-based amplification (QT-NASBA). RESULTS: 2752 individuals participated in the surveys, of whom 1.9% (51/2721) had microscopically confirmed asexual parasites and 0.4% (10/2721) had gametocytes. In contrast, QT-NASBA revealed that 32.5% (147/453) of the individuals harboured asexual parasites and 15.0% (68/453) had gametocytes. No age dependency or seasonality was observed in submicroscopic parasite carriage. DISCUSSION: Molecular detection techniques reveal that carriage of submicroscopic asexual parasite and gametocyte densities is relatively common in this low transmission area. Submicroscopic gametocytaemia is likely to be responsible for maintaining malarial transmission in the study area.