What is epidemiological triangle of diseases?

The Epidemiologic Triangle
The Centers for Disease Control and Prevention (CDC) defines an outbreak or epidemic as “the occurrence of more cases of disease, injury, or other health condition than expected in a given area or among a specific group of persons during a specific period.” When investigating how a disease spreads and how to combat it, the epidemiologic triangle can be an invaluable tool. The epidemiologic triangle is made up of three parts: agent, host and environment.

Agent:
The agent is the microorganism that actually causes the disease in question. An agent could be some form of bacteria, virus, fungus, or parasite.

Host:
The agent infects the host, which is the organism that carries the disease. A host doesn’t necessarily get sick; hosts can act as carriers for an agent without displaying any outward symptoms of the disease. Hosts get sick or carry an agent because some part of their physiology is hospitable or attractive to the agent.

Environment:
Outside factors can affect an epidemiologic outbreak as well; collectively these are referred to as the environment. The environment includes any factors that affect the spread of the disease but are not directly a part of the agent or the host. For example, the temperature in a given location might affect an agent’s ability to thrive, as might the quality of drinking water or the accessibility of adequate medical facilities.