Diseases that spread among animals or humans. Often used synonymously, and inaccurately, with “infectious”. A disease may be caused by an infectious agent and yet not be contagious. An example is Lyme disease. Among wild mice this infectious disease is contagious (with the help of ticks). However, when humans are infected, the infected human is not contagious for other humans. In this situation, humans are referred to as a “dead-end host” since the infectious agent has no capacity to move on to other susceptible humans or animals. Paratuberculosis is a contagious infectious disease of animals.