Natural history of disease with periods and prevention

The natural history of the disease refers to the evolutionary process that a pathology undergoes without the intervention of any physician. In short, it is the course of the disease from its onset to its resolution, but without medical intervention.

When there is a mild or serious alteration in the normal functioning of an organism or any of its parts, it is said to be in the presence of a disease. Every disease that manifests itself in human beings appears as the result of a dynamic process in which several factors intervene.

The sequence of events that occur in a body, from when the first actions occur until the disease develops and the result occurs, is known as the natural history of the disease.

The natural history of the disease was widely observed until a century ago, when there was not much progress in the treatment of diseases and therefore also in diagnosis.

Now that science has happily provided solutions in the field of medicine, doctors cannot easily observe this process.

However, if the natural history of disease had not been fully observed in the past, it is possible that scientists today would not have understood the course of diseases.

Therefore, they would not have found a way to detect disease early to prevent sequelae.

Periods in the natural history of the disease

The natural history of the disease is divided into two periods. The genesis period, better known as the pre-pathogenic and pathogenic period, also called the natural evolution of the disease.

– Pre-pathogenic period

The pre-pathogenic period is the pre-disease phase. At this stage, the disease has not yet developed, which means that the affected person does not have clinical symptoms, nor changes at the cellular, tissue or organic level.

But although the body is in balance, it is at this point that the human being begins to interact with the surrounding environment, and therefore, this is when the disease process begins.

At this stage, what is known as the ecological triad occurs. This is nothing more than the interaction between three essential components for the development of the disease. These are the host, agent and environment.


The host is the person or living being that allows the subsistence, accommodation and development of an infectious disease-causing agent.

It has specific characteristics that must be studied, such as age, gender, race, genetic structure, nutritional status, level of immunity, hereditary factors, among others.


In turn, the agent is any force, principle or living or inanimate substance capable of acting in a harmful way in the organism.

It is who represents the immediate or following cause of an illness. Agents can be classified in different ways. But essentially they are divided into two groups: biological and non-biological.

  • Biological agents : Biological agents are bacteria, protozoa, metazoa, viruses, fungi and / or their toxins, among others. They are characterized by being pathogenic, that is, they are capable of producing diseases.

Also because they are virulent, as they have a degree of malignancy or toxicity. They also have an antigenic power, which means they have the ability to produce an immune response in the host.

  • Non- biological agents : Non-biological agents can be divided into two main ones: chemical and physical. The former involve drugs and toxic substances such as pesticides. The latter involve mechanical force, temperature changes, radiation, electricity, noise and pressure of gases or liquids.

Non-biological agents can also be nutritional, related to inadequate diets or vitamin deficiencies. And they can also be psychological, involving stress, depression, among others.


The third component of the ecological triad is the environment. It is responsible for promoting the link between the host and the agent.

Different factors are involved in this element, which involves an individual. Only factors directly related to the physical environment should not be considered.

When talking about the effect that the environment can have on the course of the disease, there is also an interpersonal intervention, which includes couple and family relationships and close groups of friends, colleagues and even neighbors.

Another factor linked to the environment is related to the socioeconomic level. This includes community and nation social structures as well as economic development.

Finally, factors at the ideological-cultural level must be considered. In this case, the belief and knowledge structure of the community or society can also affect the individual.

– pathogenic period

The pathogenic period is that which occurs when all the circumstances and characteristics of the pre-pathogenic period coincide in a host.

In this case, the balance of the ecological triad is broken and this is when the host is affected by the disease. At this stage, cellular and tissue changes begin to occur.

Depending on the type of infection, these changes can occur quickly as a result of the multiplication of microorganisms, their virulence and ability to produce toxins.

However, in the case of chronic mental and degenerative diseases, for example, this process can be prolonged for months and even years until finally signs and symptoms of the disease occur.

The pathogenic period is divided into two stages. These are the subclinical period, also known as the incubation or latency period, and the clinical period.

– Subclinical period

It is the phase in which a causative agent invades the host. This stage is characterized by the appearance of anatomical or functional lesions, although without the presence of signs or symptoms of the disease.

It is then the time elapsed between the moment of stimulation of the disease and the moment when it becomes evident.

In communicable diseases, this phase is known as the incubation period and in chronic diseases (physical or mental), it is known as the latency period.

– clinical period

This phase begins with the first symptom or sign of the disease. This moment is called the clinical horizon. With this first manifestation, a series of symptoms or signs appear, in addition to complications and sequelae.

When talking about complications, it is when the disease involves other conditions in the body that can be heart failure, kidney failure or respiratory failure.

With regard to sequelae, it is the stage in which people usually have some kind of disability or permanent alteration in the body.

As a consequence of the disease, other elements that are part of this stage, such as damage, disability, recovery, chronicity and death, also appear.

Death is not necessarily imminent, and at any of the earlier stages the body can regain balance, i.e. health.

Along these manifestations, three stages of the clinical period can be distinguished. The first of these is the prodromal period.

This is the presence of general manifestations of the disease. In this case, the symptoms and signs are often confusing, which makes it difficult to make an exact diagnosis.

Next is the clinical period itself. This is the time when the disease is manifested by symptoms of specific signs. And thus facilitates diagnosis and management.

Finally, the resolution period is the final step. In this phase, the disease has three paths: disappears, becomes chronic or the patient dies. In the latter case, both brain and cardiac death must occur.

levels of prevention

Other elements that affect its natural evolutionary course may be involved in the development of the disease. With prevention, it is possible to interrupt the chain of events that make up the natural history of the disease, which lead to the progressive deterioration of the health of the affected individual.

Diseases can be caused by multiple risk factors. For this reason, it is not possible to control them, let alone solve them by approaching them from a given discipline. Therefore, it is necessary to place protective barriers, called levels of prevention.

When we talk about prevention, we are talking about anticipation to reduce the chances of an eventuality. And if so, the progress of this can be resolved or prevented.

Prevention can only be done based on knowledge of the natural history of the disease, since, in this case, the objective will always be to reduce the likelihood of disease progression.

There are three levels of prevention: primary level of prevention, secondary level of prevention and tertiary level of prevention.

– Level of primary prevention

This first level of prevention is applied during the period of disease genesis. That is, during the pre-pathogenic period.

In this case, the objective is to try to eliminate or reduce the risk factors present in the community. This level of prevention seeks to maintain the individual’s health and promote it through different actions.

To prevent disease and promote health, economic, educational and social measures are often applied. This includes activities related to food, hygiene education, personality development, periodic examinations, water sanitation, garbage, food, noise and everything that has to do with the environment.

Among the specific prevention measures applied are immunizations, protection against accidents, attention to personal hygiene, elimination of infectious foci, among many other things.

However, although all these activities are part of the so-called primary prevention level, it is important to note that prevention and health promotion are not the same actions.

While prevention aims to prevent the disease from deteriorating the individual’s health status, promotion is responsible for facilitating the maintenance of a person’s condition, increasing their health and well-being.

– Secondary level of prevention

This type of prevention is applied when primary prevention fails and, therefore, the individual becomes ill. This level includes measures that are applied in the latent period of the disease.

At this level of prevention, the aim is to make an early diagnosis that can lead to subsequent timely treatment.

When secondary prevention is applied, it is because it is no longer possible to apply actions that prevent the appearance of diseases. This barrier focuses on making an early diagnosis, preferably before clinical manifestations occur.

It also focuses on healing the patient before irreversible damage can occur. Or even in the prevention of complications and sequelae, among other things.

At this level of prevention, therapeutic actions are also carried out to reduce the consequences of a disease. These actions can be physical, surgical, dietary, medicinal or psychotherapeutic.

Once a disease manifests itself, a good diagnosis, which is also timely and accompanied by adequate treatment, are the best preventive measures that can be applied to prevent the disease from progressing.

– Level of tertiary prevention

This is the prevention level that is applied when it is no longer possible to apply the previous two levels. These are measures that are applied during the period of disease expression.

That is, in its symptomatic phase. In this case, acute and rehabilitation treatment is carried out. You can focus on a rehabilitation process that includes physical, socioeconomic and psychological elements.

The objective is to try to recover the sick individual, as much as possible, taking into account the abilities that remain.

Among the measures that can be applied at this level of prevention are the maximum recovery of functionality, the patient’s psychosocial change, occupational therapy, maximum use of skills, education of family members, school groups and even companies to publicize support for the disabled, Among other things.

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