The effects of interventions on parasite evolution

: (Alternative Format Thesis)

Abstract

Parasites have a significant burden on their host populations and as such, humans have devised various interventions to mitigate their effects. However, parasites can also evolve in response to interventions. Parasites have been known to adapt to many different forms of interventions, including the evolution of higher levels of virulence in response to imperfect vaccines, and resistance to antibiotics. These evolutionary responses need to be considered when applying interventions, as otherwise well-intentioned initiatives can ultimately become negative. Understanding the evolutionary consequences of interventions is important for developing evolutionarily robust responses to infectious diseases. Theoretical works have begun to investigate questions around the evolution of parasites in response to interventions, but more work is needed. In this thesis, I explore the consequences of previously unexplored interventions on parasite evolution. I explore three models of diagnostic testing, investigating when testing selects for diagnostic escape, and aim to understand the effects this may have on public health strategies. Exploring both the short-term behaviour, whether detection avoidance arises during the epidemic phase, and long-term behaviour, whether detection avoidance arises during the endemic phase. I find key thresholds for determining when the evolution of diagnostic escape will be selected for, as well as showing that diagnostic testing is beneficial even despite diagnostic escape, as the proportion of the population infected always decreases. I also explore the effects of introducing hyperparasites, parasites whose hosts are themselves parasites, on the evolution of parasite virulence, and parasite susceptibility to hyperparasite infection. Here we seek to understand the long-term consequences of hyperparasite introduction, both on the host population and the diversity seen within the parasite population. I find that the introduction of hyperparasites can have a net positive or negative effect on the host population, and that these regions of positive and negative eAects form a bistable region, which has the potential to lead to a hysteresis effect.

Date of Award	26 Jun 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Ben Ashby (Supervisor) & Nicholas Priest (Supervisor)