Evolutionary processes underlying the diversity and distribution of primate malarias - a perspective on ecological and epidemiological dynamics

Abstract

In this dissertation, I explore host-parasite coevolution in a complex pathogen system that presents a source of current and potential human parasites. I utilize a variety of empirical, laboratory and theoretical methods to investigate determinants of the host associations and diversity of primate malarias. A meta-analysis of malaria parasite surveys reveals gaps in phylogenetic and geographic sampling effort. Nevertheless, several primate clades are well surveyed and these can be used to make robust predictions about coevolutionary host-parasite events. These results highlight the permeability of primate host species barriers and point to an important role of vectors for facilitating host switching. Phylogeographic analysis reinforces that geographic signatures are observable in generalist parasites- meaning host species availability is more significant than host phylogeny in determining transmission cycles. Primates do not serve as passive hosts for these infections, and results show evidence for malaria-driven selection of an alpha globin variant among long-tailed macaques, Macaca fascicularis. The alpha globin variant likely protects against death from particular malaria parasites, and thus offers a novel route to protection against malaria, analogous to mutations in human populations, but with superior outcomes. Following spillover, the emergence of new pathogens in human populations is often abrupt and requires rapid application of novel treatment and prevention protocols. The final chapter highlights delays that are often associated with changes in policy and underscores the importance of rapid implementation. Overall, the results presented here emphasize the permeability of primate host barriers in this primate-malaria system, highlight the frequent occurrence of host switching and the potential role of host adaptation in the radiation of malarias, and indicate routes for clinical responses to changes in human disease landscapes. This system shows that it is essential to study the ecological processes underlying variation in host-parasite associations to understand zoonotic host switching. Exploitation of novel host species by parasites (including pathogens) raise fundamental evolutionary questions. The current paradigm is that parasites are adapted to specific hosts and have a reduced ability to infect distantly related host species. These general rules don't apply to primate malarias, suggesting multi-host pathogen systems have additional complexities influencing their evolution and ecology.