Eco-evolutionary modelling of infectious disease and host resistance
Abstract
In this work we take an evolutionary invasion analysis approach to modelling evolution
and use it to describe the selection pressures underlying epidemiological traits
in natural host populations harboring endemic infections. Throughout this work a
logistic form for host-birth rate allows for disease dependent population dynamics
so that the detrimental e ects of infection can be modelled and we also consider
the more neglected detrimental e ect whereby infection is linked to infertility. To
begin with we give a theoretical introduction to the framework of adaptive dynamics
and illustrate it through the established example of the evolution of parasite
virulence. We then extend the results to account for condition dependent virulence
which is an interaction between host condition (i.e. host stress) and virulence, that
has recently generated much attention from empiricists. Many natural systems are
seasonal, potentially leading to seasonal stress, and we show how to conduct a study
for seasonal host populations and analyse its role in the evolution of density dependent
virulence. We then turn our attention to the evolution of resistance beginning
with a perspective on the relationship between investment in acquired immunity and
the lifespan of hosts and parasites. In our penultimate chapter we derive explicit
expressions for optimal investment in the various modes of resistance for a range
of epidemiological scenarios. These expressions are then key to understanding our
nal chapter where we elaborate further on the established theory by allowing for
parasite diversity. The nal chapter highlights the central role played by speci city
in the evolution of host defence. Since our approach throughout has been to build
complexity onto a baseline model we conclude our discussion with a short section
interpreting established results on the coevolution of virulence and resistance from
the perspective of our results on the evolution of virulence and resistance.