A syndemic involves two or more afflictions that, by interacting synergistically, contribute to excess burdens of disease. A syndemic approach to prevention, meanwhile, focuses on connections among health-related problems, considers those connections when developing health policies, and aligns with forces for social change. In this short report, we expand the syndemic concept to acknowledge the extent to which animal health connects with human health and, with reference to existing publications, we demonstrate the pertinence of this expanded definition for a syndemic approach to prevention. Our demonstration assumes practical importance in relation to the concept of 'one health', which many prominent veterinary and human health scientists have recently endorsed as a sound basis for redressing human diseases, animal diseases, and environmental degradation worldwide. While social scientists have mostly ignored animal health, few 'one health' proponents have emphasized social conditions or involved social scientists. By explicitly accommodating animal-human connections in our expanded conceptualization of a syndemic, we hope to help create a space in which human health, veterinary, and social scientists may learn from one another, collaborate in research, and cooperate to clear the way for innovations in prevention.