[Levels of malaria transmission: methods and parameters].

Evaluation of malaria transmission levels is necessary to compare ecologically diverse areas and to assess the effectiveness of efforts to control the disease. The purpose of this report is to describe useful techniques for descriptive epidemiology and potentially pertinent indicators regarding the three links in the epidemiological chain: transmission from mosquito to man, transmission from man to mosquito, and sporogonic cycle. Standards for evaluation of transmission from mosquito to man are now well established. Techniques and resulting data, mostly entomological, have been validated in numerous multicenter and multidiscipline studies before and after implementation of control measurements. Evaluation of transmission from man to mosquito has not yet been extensively studied. Gametocyte index does not appear to be a good indicator of infectivity in mosquitoes. Two other parameters that have been proposed in the literature are rate of human infectivity to mosquitoes and probability that a bloodmeal will be infectious. However these evaluation techniques have been neither subjected to comparative study nor validated in epidemiological surveys. The third factor for evaluation of malaria transmission levels involves sexual development of the gametocytes (sporogonic cycle) in the vector. Two indicators that might be useful in this regard are quantification of early-stage parasites in the stomach of the mosquito and study of blood factors in subjects in whom inhibition transmission has been documented. Since these methods have been used only sporadically, further study will be needed to validate this approach to evaluate transmission level.