Epidemiology of Infectious Diseases: Reservoir of Agent (Page 1 of 5) Reservoir of the agent is the normal habitat in which an infectious agent lives, multiplies, and grows. Reservoirs may include humans, animals, and environment. Two major human sources of infection are acute clinical cases and carriers. The acute clinical cases usually have overt symptoms or disabilities that reduce their contact with other people. Carriers are people who have disease with no overt signs or symptoms. They may be unaware they are carriers and therefore take no special precautions to prevent transmission.