Immunity and Virulence in Bird-Parasite Interactions

The interaction between hosts and parasites is characterized by the evolution of reciproca adaptations aiming at reducing the cost of infection (from the host point of view) and to optimize host exploitation (from the parasite point of view). Within this co-evolutionary scenario, the immune system takes a central role. The immune system has evolved to fight off parasitic attacks. However, immune defences cannot be deployed without costs which set a limit to the protective effect of immunity. Moreover, immune defences impose strong selection pressures on the parasite and can favour the evo- lution of more virulent pathogen strains. In this article, we will discuss these different issues focusing on host-pathogen interactions involving birds and their parasites.