|Agent, Host and Environment Model of Causation||To Prevention theme page|
1. Core Knowledge
This triangular model was developed for infectious disease. Disease spread requires a susceptible host and an infective agent, in an environment that brings them together:
Note that the model is also helpful in thinking about non-communicable diseases:
- An occupational injury is more likely when there is a dangerous agent (chemical, biological or physical hazard), a susceptible host (the worker who is inadequately protected) and a hazardous working environment (poor supervision; inadequate culture of safety, etc.).
- Cardiovascular disease can arise in a susceptible person who is exposed to an agent such as tobacco, an inappropriate diet, etc, in an environment that supports this (e.g. poverty, under certain cultural norms, etc.)
Applying the triad model to prevention, to prevent the disease it should be sufficient to modify one (but preferably more than one) of the factors on the corners of the triangle: to immunize the host, or to develop a protective environment, or to remove the agent. These fall under health protection or hazard control measures.
If you cannot remove or modify the corners of the triangle you can also prevent disease by breaking the lines: remove the connection between the agent and the environment (e.g. install window screens to keep malarial mosquitoes out of the house); protect the host from coming into contact with the agent (use bug spray or mosquito nets); move the host to a different environment (leave town!). This idea is taken up in the Source - Path - Receiver model in occupational health.