Zoonotic diseases, or diseases that are transmitted from wildlife to humans, provide clear evidence that human health does not exist in a vacuum, but rather results from a complex interplay between humans, other organisms, and their shared environment. This interplay is the domain of disease ecology, or the study of host-pathogen interactions as they occur in an ecosystem. This case study introduces students to the field by focusing on two seemingly unrelated diseases in a forest ecosystem: sudden aspen decline and hantavirus cardiopulmonary syndrome caused by Sin Nombre virus (SNV). Students interpret real data from the primary scientific literature, make predictions, and then evaluate those predictions given the evidence presented by the researchers. Students practice quantitative data literacy skills and solidify their understanding of direct and indirect effects. The case was developed for a general ecology course at the undergraduate level but could also be used in courses such as introductory biology, population biology, community ecology, or disease ecology.