Systematic temporal changes in host susceptibility to infection: demographic mechanisms.

Simple mathematical models are developed to examine the influence of variability in host susceptibility to infection, on the dynamics of host-parasite population interactions. When hosts differ in their innate susceptibility (at birth), to infection by a specific parasite, the average susceptibility of the host population as a whole may show systematic changes through time. Such patterns may arise as a result of demographic factors associated with the interaction between host and parasite populations, in the absence of inheritance mechanisms (a genetic component) or acquired resistance (an immunological component). The general significance of this observation is discussed in terms of the coevolution of host-parasite associations.