Parasites are ubiquitous in nature and can have profound impacts on host populations. Primates are among the most threatened animals in the world, yet our understanding of the baseline epidemiological factors that naturally contribute to infection dynamics, and thus our ability to predict specific disease outcomes, remains poor. In this invited review, I argue for the necessity of good empirical model systems through which just such an understanding can be approached. I highlight the utility of one such model system that is both parsimonious and highly accessible: the Japanese macaque and its gastrointestinal nematode parasites as a single-host, multi-parasite study system. I explore epidemiological patterns of nematode infection in Japanese macaques and re-introduce the concept of parasite aggregation in an attempt to re-frame current understanding of, as well as re-direct future questions about, primate-parasite interactions as host and parasite population processes. Despite the fact that parasite aggregation has critical implications for understanding the processes involved in both host and parasite regulation, including the various cascading ecological effects regulation can have, this approach is seldom used in studies of primate parasite ecology. Ultimately, this review aims to remind us that parasitism is fundamentally an ecological interaction and that, like predation and competition, parasites play important roles in mediating ecosystem health, including the various functional roles that primates may fulfil.