The Reservoir for Infectious Agents is the principal habitat where a specific infectious agent lives and multiplies. The reservoir is necessary for the infectious agent either to survive, or to multiply in sufficient amount to be transmitted to a susceptible host. Examples may include primates (including human beings), the reservoir of pathogens such as hepatitis A virus, hepatitis B virus, Polio virus (all 3 types), Bordetella pertussis, Corynebacterium diphtheria, etc. 

Other micro organisms have larger animal reservoirs, e.g. Salmonella species can be found in almost every animal. The environment contains a large number of reservoirs: soil, the reservoir for Clostridium tetani or water, the reservoir for Legionella pneumophila.

 In a number of articles the concept of 'source' and 'reservoir' are used as synonyms, though strictly speaking they are not. In this FEMWIKI we consider a source as the starting point of a transmission route; it usually can be found at a specific time in a specific place (in other words: it often has 'an address'). Sources can be part of a reservoir. For example: warm water systems (generic) are known to be reservoirs for legionella and the shower in room 911 of Hotel X was found the source of a number of legionella infections.

It is important to know the reservoir of pathogens, as this may offer opportunities for control. For example, a disease like smallpox (variola major) could be eradicated from this planet, in part because humans were the main reservoir. By immunizing the majority of the reservoir population, and by rigorously keeping infectious patients isolated and immunizing contacts, the smallpox virus could no longer survive in nature. This is one of public health's great achievements and currently similar attempts are underway to do the same with poliovirus. 

References:

  1. David L. Heymann (editor). Control of Communicable Diseases Manual. APHA, 2008