A reservoir is any organism, population or environment in which a pathogen normally lives and multiplies, serving as a long‑term source of infection for other hosts.
Explanation
Identifying the reservoir of a disease is crucial for understanding its ecology and controlling transmission. Reservoirs harbour pathogens without necessarily showing clinical disease, allowing the agent to persist in nature. Human reservoirs include symptomatic and asymptomatic carriers who can transmit pathogens such as Mycobacterium tuberculosis, Neisseria gonorrhoeae or typhoid Salmonella. Animal reservoirs are responsible for many zoonoses; rodents maintain Yersinia pestis (plague), dogs and bats harbour rabies virus, and white‑footed mice and deer support the life cycle of Borrelia burgdorferi causing Lyme disease. Environmental reservoirs encompass soil, water and vegetation. Clostridial spores persist in soil, making it a reservoir for tetanus and botulism, while brackish water acts as a reservoir for Vibrio cholerae. Reservoirs differ from vectors; a vector actively transmits a pathogen between hosts but may not sustain long‑term amplification. Some reservoirs overlap with vectors, such as ticks that maintain and transmit tick‑borne encephalitis virus. Recognising whether a pathogen has a single reservoir or multiple ones informs interventions such as vaccination, environmental sanitation or wildlife management.
Types and Examples
Human reservoirs include chronic carriers of hepatitis B virus and HIV who can spread infection through blood or sexual contact. Domestic dogs are the main reservoir for human rabies in many developing countries, whereas vampire bats serve that role in parts of Latin America. Migratory waterfowl act as reservoirs for influenza A viruses, seeding outbreaks in poultry and humans. Soil contaminated with bird or bat droppings supports the environmental reservoir of Histoplasma capsulatum. Standing water in air conditioning systems can be a reservoir for Legionella pneumophila, causing Legionnaires’ disease. Understanding these associations guides targeted control measures such as animal vaccination campaigns, safe water and food handling, and public health surveillance.
The concept of a reservoir emphasises that pathogens often persist beyond the individuals they infect. By identifying and controlling reservoirs, public health efforts can break transmission cycles and reduce the incidence of infectious diseases.
Related Terms: Carrier, Vector, Zoonosis, Environment, Pathogen