[The concept of risk in parasitic diseases with special reference to malaria (author's transl)].

The concept of risk, its components and their interrelationship are described. Emphasis has been placed on the value of the variables to be taken into account in the selection of intervention measures: -- for the mosquito: the daily frequency of blood meals taken from man, the duration of the sporogonic cycle, the daily survival rate and the proportion of people with gametocytes in the peripheral blood; -- for man: the number of anophelines feeding on man in a unit of time, the proportion of mosquitoes with sporozoïtes in their salivary glands and the proportion of sporozoïtes able to infect man. Using these variables, it is possible to calculate the various risks incurred both by man and vector. Whenever possible and in order to be of greater value, the interventions should be directed against the variable which have the highest power. However, in view of the complexity of relations, it is better to construct a mathematical model able to simulate with the use of a computer, real epidemiological situations. A model has been recently developed for the study of the malaria dynamics and for the comparative evaluation of various methods of control.