Abstract
Molecular epidemiology has largely been investigated from the parasite side, therefore contributing to a better understanding of transmission patterns and factors influencing disease spread. From the hosts’ point of view, molecular epidemiology has lead to the identification of components of susceptibility and resistance to infectious diseases. In this chapter, we aim to explain why resistance to infections exhibits such a remarkable degree of polymorphism while being resistant obviously confers a high selective advantage to hosts. In this context, we develop host molecular epidemiology with regard to the concepts of evolutionary biology and immunoecology. We detail the mechanisms that are likely to underlie the variable degrees of host resistance polymorphism observed among natural populations. Particular attention is given to recently emphasized topics, including the risks of immunopathology, the spatial structure of populations, the impact of neutral evolutionary processes and the phenotypic plasticity of resistance. We evidence the consequences of this polymorphism for disease epidemiology both from empirical examples and genetic epidemiological modelling of resistance evolution. We stress the numerous gaps that remain to be explored to understand these patterns of disease resistance polymorphism. We particularly emphasize the cruel lack of theoretical predictions and data that have focused on biological invasions and hybridisation, two biological situations of main interest for emergence