Doctoral Dissertation Improvement: Rodent-human Cohabitation and Disease Transfer in Sedentary Human Populations

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Zoonotic diseases are those that are transmitted between humans and other animals, and they make up more than half of all infectious diseases in humans. Rodents are one of the richest sources of these zoonoses, yet both theoretical and empirical explanations are scant for why rodents have had such a great impact on human health and why some rodent species readily spread these diseases, while others do not. To better understand the epidemiological relationships that humans have with rodents, this dissertation research seeks to determine whether rodents that live in and around human homes (in an ecological relationship termed "commensalism") pose a greater threat to human health than wild rodents that are not commensal. After determining this, the research team will investigate hypotheses for how the behavior and ecology of different rodent species influence patterns of coexistence with humans. Doing so also will allow the researchers to propose an underlying cause for rodent commensalism, whether mainly for shelter and protection, or for access to food.In order to maximize both the quantity and quality of data, the research will focus on rural populations in central Kenya, where over twenty endemic rodent species overlap with humans in a single habitat and show varying degrees of infection with zoonotic pathogens. This diversity in rodent species and pathogens is unparalleled within the United States, and it provides an ideal natural setting in which to identify generalizable effects of commensalism on disease transmission. To determine differences in infection due to commensalism, the doctoral student researcher (Collin McCabe, under the supervision of Dr. Richard Wrangham, Harvard University) will capture rodents within homes and in nearby undisturbed habitats. Blood will be drawn from these animals, and these samples will be sent to a lab in the United States for zoonotic pathogen detection. The researchers will then assess the risk-taking behavior of the animals and also will evaluate their diets to determine the most likely explanation for these rodents' cohabitation with humans. By defining the patterns of infection and exposure among free-living rodents and humans, results of this research will suggest whether wild or commensal rodents present a bigger disease risk to humans, and by understanding the factors that influence commensalism, public health agencies can focus control efforts on the most likely areas of human-rodent overlap. In today's highly connected world, the health concerns arising from new disease outbreaks are truly global. Thus, by contributing to awareness and control of zoonotic outbreaks abroad, this study also will contribute to American health security.