A reservoir is a site or habitat where an infectious agent or pathogen "lives, grows, and multiplies".

Reservoir of an infectious agent

Transmission occurs when an infectious agent or pathogen exits its reservoir through a portal of exit, is carried to a portal of entry through a mode of transmission, and infects a susceptible host. 

Transmission of Infection

The traditional sequence in which infectious disease results from the interaction of agent, host, and environment.


University of Michigan - Ann Arbor

Traditional model for infectious disease that consits of an agent/pathogen, a susceptible host, and an environment.  Disease is a result of an agent/pathogen and a susceptible host interacting in an environment that enables transmission. 

Epidemiological Triangle

Centers for Disease Control and Prevention. (n.d.). Centers for Disease control and Prevention. Centers for Disease Control and Prevention. https://www.cdc.gov/. 

Centers for Disease Control and Prevention

In infectious disease epidemiology, an agent is an infectious organism or pathogen, such as a virus, bacterium, paraiste, etc. that can cause disease. 
Some factors that can influence an agent's ability to cause disease include: pathogenicity, virulence, addictive qualities, infectivity, ability to survive outside body, susceptibility to antibiotics, etc. 


Agent/Pathogen

Qualities that can affect an environment or its susceptibility include: climate, building design, sanitation, social environment, access to health care, population density, etc.


Environment

Chain of Infection

Examples of factors that may make a host more susceptible to infection or disease are genetics, resiliency, nutritional status, prior exposure, age, co-infection, etc.


Host susceptibility

A vector is an organism which transmits infection by conveying the pathogen from one host to another without causing disease itself, may be part of the infectious process.

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