The primary means to define any disease is by naming a pathogen or agent that negatively affects the health of the host organism. Another assumed, but often overlooked, determinant of disease is the environment, which includes deleterious physical and social effects on mankind. The disease triangle is a conceptual model that shows the interactions between the environment, the host and an infectious (or abiotic) agent. This model can be used to predict epidemiological outcomes in plant health and public health, both in local and global communities. Here, the Irish potato famine of the mid-nineteenth century is used as an example to show how the disease triangle, originally devised to interpret plant disease outcomes, can be applied to public health. In parallel, malaria is used to discuss the role of the environment in disease transmission and control. In both examples, the disease triangle is used as a tool to discuss parameters that influence socioeconomic outcomes as a result of host-pathogen interactions involving plants and humans.