In recent years, the field of population biology, encompassing both ecology and evolution and its intersections, has increasingly recognized disease as a centrally important phenomenon. For example, disease may influence the population dynamics of host organisms and the structure of natural communities, and may be an important agent of natural selection and thus evolution. So, there is a growing body of both theoretical and empirical scientific literature on host-parasite population interactions. The organisms studied in this body of work range across the biological spectrum, including microscopic disease agents, and hosts such as wild herbaceous plants, crops, forestry trees, wild animals, insect crop pests, domestic cows, humans - to name just a few.
Human disease deserves a special mention.
Growing out of this general recognition of the key role of disease in natural populations and the application of evolutionary principles to it, there has been in the past 10 years or so a vigorous effort to apply Darwinian thinking to human disease. This new field is called Darwinian medicine.