Ecological triad: definition, elements and examples

The concept of ecological triad refers to the interactions that exist between the different elements that intervene when a disease occurs , mainly but not always, of an infectious nature. It is called a triad because there are three elements that intervene during the disease process, and ecological, because these three elements or factors share an ecological character. It is a model that allows a better understanding of the elements and processes that characterize diseases, as well as the possibility of identifying patterns of action to combat these diseases.

In the next sections of the article we will see in detail what are the three elements that make up the ecological triad, as well as some examples of diseases and their associated ecological triads.

As we have seen in the previous section, the elements that make up the ecological or epidemiological triad are three. These are usually represented in the form of a triangle, or as a balance, specifying the relationships that exist between them and the factors that constitute each element of the triad, these being:

• Epidemiological agent.
• Epidemiological host.
• Epidemiological environment.

Let’s see in the next section what each of the three elements of the ecological triad consist of.

Epidemiological agents are considered each and every one of the different organisms that are capable of developing diseases in other organisms that act as hosts of the disease. The great variety of epidemiological agents that exist are included within bacteria, viruses or other groups of microscopic parasites, as is the case of some protozoa.

These epidemiological agents share a series of characteristics that make them organisms capable of causing disease. Among the characteristics of the epidemiological agents are:

• Pathogenicity.
• Infectivity.
• Virulence.
• Antigenic power or immunogenicity.
• Lethality.
• Mutation.

At this point, we recommend you also read this other article on Parasitism: definition and examples .

The second element of the ecological triad is the epidemiological host or host susceptible to contracting the disease caused by the infection of the epidemiological agent.

Both humans and animals and other living organisms can be considered as epidemiological hosts, whose resistance and / or immunity mechanisms at the time of infection are deficient and favor their susceptibility to contracting a disease. This susceptibility can depend on different intrinsic characteristics of the hosts, such as age, heredity, environmental conditions, nutrition and hormonal imbalance.

As for the routes of transmission of the disease, that is, the way in which the agent infects the host, they are usually the respiratory, digestive, urinary, and even through the skin and mucous membranes.

The environment plays a very important role in the process of infection and spread of diseases, since, depending on the environmental conditions , infectious agents are capable or not of reaching the hosts.

In this way, the environment as an element of the epidemiological triad includes both physical factors typical of the environment (soil, water, wind, objects), as well as biotic factors (animals, food, or even human beings); which act as vectors for the transmission of the disease.

On many occasions, a single change in the environmental and / or geographical conditions included within the environment, are capable of allowing or preventing the spread of infectious diseases.

Now that we know the three elements of the ecological triad , it is necessary to highlight the model or route that infectious agents follow from the source of infection to the hosts. This model of interrelations is called the epidemiological chain , which allows knowing each and every one of the different links and elements that intervene (directly or indirectly) in the development of a disease and its consequent transmission mechanism.

The epidemiological chain fulfills a really important function, since thanks to it it is possible to identify which element of the triad must be acted upon (through prevention and / or control measures), to deal with diseases. Thus, the six fundamental links in the epidemiological chain are:

1. Infectious agent.
2. Reservoir.
3. Exit port of the infectious agent from the reservoir.
4. Transmission route.
5. Entrance door from the agent to the guest.
6. Guest.

To better understand what the ecological triad is, let’s look at the example of some of the best-known diseases and their associated ecological triad :

Example of dengue ecological triad

• Agent: dengue virus.
• Environment vector: Aedes aegypti mosquito .
• Host: human.

Example of ecological triad of diabetes

• Agent: sugar.
• Environment vector: sugary drinks.
• Host: human.

Example of ecological triad of influenza

• Agent: influenza virus.
• Environment vector: animal.
• Host: human.

We recommend that you learn more about this topic with these other AgroCorrn articles on Are viruses living beings? and about the Difference between viruses and bacteria .

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