Anthropological research in recent years has examined how single diseases such as Aids, tuberculosis, measles, malaria and leprosy are conceptualized by laypersons in non-Western societies. But how is disease transmission itself interpreted in other cultures? Data from ethnographical studies in Côte d'Ivoire and the Afro-Brazilian culture in Bahia, Brazil show that the interpretations of contagion and preventive practices cut across society involving five main relationships: empirical and analogical thinking, symbolic factors and social organization, the concept of person and body elements, natural and supernatural powers and individual and contextual factors. There is not a general theory, such as Pasteur's theory of germs. Instead,contagion presents itself as a transversal, multidimensional concept crossing and interconnecting society and culture. Public health programmes aimed at controlling infectious diseases need first to understand how contagion is conceptualized by laypersons, the extent to which diseases are considered infectious and the relation between perceptions and preventive practices. This would help in implementing infectious disease control programmes within local contexts based on meaningful community participation.