Question

An important point about the agent-host-environment model (the epidemiologic triangle) of epidemiologic investigation is that:

A. the agent is not as important a factor in disease causality as the host or the environment.

B. diseases are multi-causal.

C. it is necessary that the agent is linked to both the host and the environment and that the agent is present in every case of the disease.

D. in order to prove causality, which is a difficult task, the researcher must prove that the agent, host and environmental factors under investigation are both necessary and sufficient to cause the disease being studied.

Answer 1

The correct option is-Option-(B)

Diseases are multi-causal.

According to the epidemiological triad, the disease occurs when there is a disturbance in the equilibrium between agent, host, and environment.

This equilibrium between these triads suggests the theory of multifactorial causation(web of causation) which means the disease is not only caused by an organism but also predisposed by many other factors contributing to its occurrence. These predisposing factors are social, cultural, genetic, psychological.

These predisposing factors are known as Risk-factors in this theory of multifactorial causation and it is linked to human lifestyle and behavior. It can be modifiable (can be altered) and non-modifiable (cannot be altered).

For example- Smoking, fat intake, lack of physical exercise, obesity are risk or predisposing factors in the web of causation of Coronary Heart Disease.

Option- A is incorrect because the agent is as important as the host and environment in disease causality.

Option- C - Agent is present in all the cases but the presence of that agent alone is not always sufficient to cause disease.

Option- D- It is not necessary that all the 3 are involved in the causality of disease means change in any of the single factor can disrupt the equilibrium and leads to disease.