The absolute necessity for rational therapy in the face of rampant drug resistance places increasing importance on the accuracy of malaria diagnosis. Giemsa microscopy and rapid diagnostic tests (RDTs) represent the two diagnostics most likely to have the largest impact on malaria control today. These two methods, each with characteristic strengths and limitations, together represent the best hope for accurate diagnosis as a key component of successful malaria control. This review addresses the quality issues with current malaria diagnostics and presents data from recent rapid diagnostic test trials. Reduction of malaria morbidity and drug resistance intensity plus the associated economic loss of these two factors require urgent scaling up of the quality of parasite-based diagnostic methods. An investment in anti-malarial drug development or malaria vaccine development should be accompanied by a parallel commitment to improve diagnostic tools and their availability to people living in malarious areas.

Submicroscopic Plasmodium falciparum gametocytemia (<5,000 gametocytes/mL) is common and may result in mosquito infection. We assessed the relation between gametocyte density and mosquito infection under experimental and field conditions using real-time quantitative nucleic acid sequence-based amplification (QT-NASBA) for gametocyte quantification. Serial dilutions of NF54 P. falciparum gametocytes showed a positive association between gametocyte density and the proportion of infected mosquitoes (beta=6.1; 95% confidence interval [CI], 2.7-9.6; P=0.001). Successful infection became unlikely below an estimated density of 250-300 gametocytes/mL. In the field, blood samples of 100 naturally infected children showed a positive association between gametocyte density and oocyst counts in mosquitoes (beta=0.38; 95% CI, 0.14-0.61; P=0.002). The relative contribution to malaria transmission was similar for carriers with submicroscopic and microscopic gametocytemia. Our results show that transmission occurs efficiently at submicroscopic gametocyte densities and that carriers harboring submicroscopic gametocytemia constitute a considerable proportion of the human infectious reservoir.