Tracing zoonotic parasite infections throughout human evolution

Abstract

Parasites are useful pathogens to explore human-animal interactions because they have diverse life cycles that often rely on both as hosts. Moreover, some species are not host specific and are transmitted between animals and humans. Today most emerging infections are zoonoses. Here, we take a specific look at the emergence and re-emergence of zoonotic parasites throughout hominin evolution and consider evolutionary, cultural, and ecological factors involved in this. We combine genetic studies focused on molecular phylogenetic reconstructions, most often using the ribosomal RNA gene unit and mitochondrial genes from modern parasites, archaeological evidence in the form of preserved parasite eggs and antigens in skeletal and mummified remains, and modern epidemiological data to explore parasite infections throughout hominin evolution. We point out the considerably ancient origins of some key zoonotic parasites and their long coevolutionary history with humans, and discuss factors contributing to the presence of many zoonotic parasites in the past and today including dietary preferences, urbanization, waste disposal, and the population density of both humans and domesticated animals.