ECOLOGICAL TRIAD: DEFINITION AND COMPONENTS - MEDICINE - 2024

The ecological triad is one of the traditional models, developed by scientists, to study conditions related to health.

Previously, the epidemiological triad only explained the elements that influenced the contraction and spread of infectious diseases. However, now this model is also applicable to non-infectious diseases.

Image recovered from Occupational Focus.

The ecological triad represents the interaction between three elements that intervene in a disease: the causative agent, the host or affected individual, and the environment.

Elements of the ecological triad

The elements of the ecological triad answer three questions: "what?", "Who?" and where?". The "what?" corresponds to the agent, the "who?" the guest and the "where?" To the environment.

Agent

Originally, the term "agent" referred to the microorganism (virus or bacteria, for example) that caused a disease. However, with the expansion of the focus of epidemiology, the term now also includes chemical and physical compounds that can cause disease.

In non-infectious diseases, the agents can be behaviors that threaten health, inappropriate practices or exposure to dangerous situations or substances. In this sense, the agents can be classified into:

1. Biologicals, such as bacteria, viruses, some fungi, and protozoa (parasites).
2. Chemicals, like poison.
3. Physical, such as trauma from a car accident.
4. Nutritional, such as malnutrition, anorexia, and bulimia.
5. Energetic, such as thermal energy.

As a general rule, the agent must be present for the disease to occur. However, sometimes, the presence of this element is not enough to trigger the disease.

For disease to occur, a combination of what are known as "sufficient factors" must be present, including the host and environmental conditions.

Guest

The host is the organism, usually human or animal, that can contract the disease. Likewise, the term "host" also refers to vectors, organisms in which an agent lives and that function as intermediaries to transmit the disease to other organisms. In this sense, guests can be of two types:

1. Intermediaries: Those that the agent needs to develop in its larval phase.
2. Definitive: Organisms in which the agent lives in its adult phase.

It should be noted that this classification of agents applies only to infectious diseases.

There are a series of elements that can influence the susceptibility of the host to contract a disease, such as the socio-economic status, lifestyle, behavior, age and sex of the organism.

Ambient

The environment refers to all the elements that are external to the guest. Environmental factors affect both agents and hosts and can increase or decrease the chance of contracting the disease. Environmental factors can be of different types:

1. Physical: seasons of the year, weather conditions, temperature, rainfall, among others.
2. Location: rural and urban areas.
3. Biological: presence or absence of animals.
4. Socio-economic: access to the health system, sanitation, urban cleaning, among others.
5. Pollution: water, air, soil.

Ecological triad scheme

The triad is represented as a triangle and each vertex of this figure represents one of the elements that intervene in a disease, that is, the agent, the host and the environment.

Other authors include vectors, organisms that transmit the disease, but do not necessarily suffer from it, as an element alien to the triad but that influences each of the elements of the triangle, while being influenced by them.

Finally, there are those who consider that in the center of the triangle is the time factor. Time refers to the incubation period, which is the period from when the host is infected until the first symptoms appear.

Similarly, time can refer to the period from the onset of the disease to the recovery or death of the host.

Examples of ecological triads

As previously stated, ecological triads can apply to both infectious and non-infectious diseases. Here are three examples of triads.

Example of infectious disease: Malaria

One of the typical examples of the ecological triad is malaria. Malaria or malaria is a parasitic disease caused by protozoa belonging to the genus Plasmodium (agent) and which is transmitted through the bites of the female Anopheles mosquito (vector). It only affects humans (hosts).

Example of injury or trauma: burns

Take the case of a child who suffered a skin burn while bathing in hot water. In this case, the child is the host, the agent is thermal energy, and the vector is hot water.

Regarding the environmental factors that influence this process, one could mention the absence of supervision by an adult or the failure of the heating system.

Example of an ecological triad applied to diseases related to cigarette smoking

Smoking cigarettes can be the cause of various diseases (such as lung or laryngeal cancer). In this sense, humans who smoke are hosts for these diseases; cigarettes are the agents, while the people in charge of producing and distributing cigarettes act as vectors.

Finally, the influencing environmental factors could be the advertising that promotes cigarette consumption and the social pressure generated between friends, two elements that increase the exposure of the guests.

References

1. Epidemologic Triad. Retrieved on April 5, 2017, from campusvirtualsp.org.
2. Epidemologic Triad. Retrieved on April 5, 2017, from onlinecourses.science.psu.edu.
3. Forjouh, Samuel. Principles of Epidemology. Retrieved on April 5, 2017, from researchers.sw.org.
4. Epidemology: An Introduction. Retrieved on April 5, 2017, from open.edu.
5. How the triad interacts. Retrieved on April 5, 2017, from campusvirtualsp.org.
6. Epidemology. Lesson 1: Understanding the Epidemologic Triangle through Infection Disease. Retrieved on April 5, 2017, from cdc.gov.
7. Szekely, Brian. The Public Health Triad. Retrieved on April 5, 2017, from jblearning.com.