Traditional triangle of epidemiology


Traditionaltriangle of epidemiology



Epidemiologyis the study of diseases, how they affect different people and why.The traditional triangle of epidemiology consists of threecomponents external agent, host and an environment (Merrill, 2010).The agent and host come together to cause a disease in the host. AVector transmits infection by transferring pathogen from one host tothe other without infecting itself. A change in any component willalter the equilibrium by either increasing or decreasing theoccurrence of a disease. In a steady state of equilibrium of thetriangle, each component affects and is being affected by the othercomponents (Merrill, 2010).

Thefirst component of traditional triangle is the infectious agent. Thisis a microorganism that causes infection. Their characteristicsinclude pathogenicity and infectious doses. The behaviors andsymptoms of the patient can influence the possibility of exposure ofan agent to the other host. Examples of living agents includebacteria and viruses (Merrill, 2010). For instance, a vector formalaria is the Anophelesmosquito that carry plasmodium parasite of an infected host to thenext causing infection to the other host.

Susceptiblehost is another component. This is a person with insufficientimmunity against a certain infectious agent to prevent contracting adisease when subjected to an infectious agent. The host must beexposed to an infected source to acquire the infection (Merrill,2010). The host`s innate and acquired responses may impact itsability to prevent the disease when exposed to an infectious agentcausing the immunization status and generic factors to be altered.Examples of hosts are people, animals and plants (Merrill, 2010).

Thethird component of traditional triangle of epidemiology is theenvironment. This includes all the external factors of either thehost or the infectious agent that impede transmission or exposure tothe infectious agent from the patient to the host. These factorsinclude climate, dust, altitude and time (Merrill, 2010).


Merrill,R. M. (2010). Introductionto epidemiology.Sudbury, Mass: Jones and Bartlett Publishers.