Relationship Agents, Human, Environment and Disease

The study of the interrelationships between living things with their environment called Ecology. Ecological learning the intricacies of the types (species) of living things with the environment called autecological, while ecological learning the intricacies several types of living things at once in a habitat or community called Sinecology. For example, urban ecology, forests, waters, and so on. Meanwhile, the study of the interrelationships between man and his environment called Human Ecology.

Interaction between living organisms with abiotic environment in a community that is based on the diet, the bio-diversity, and recycling for survival called Ecosystem. Environment on humans and other living things can be divided into two, namely:

Internal Environment

Internal environment is the physiological and biochemical processes that take place in the human body at any given moment are also able to adapt to changes and circumstances that occurred outside the body for survival also called homeostasis. For example, the temperature changes from hot to cold.

External Environment

The external environment is everything animate or inanimate form, the energy space, the social, economic, and culture can bring influence to human life on this earth.

Environmental pollution

Environmental pollution is entered or the inclusion of living organism, substances, energy, or other components into the environment or changing the order of the environment by human activity or by natural processes so that environmental quality declines to a certain level which causes the environment to be less or no longer works in accordance with designation. For example, the disposal of industrial waste into rivers and the ocean will lead to changes in the aquatic ecosystem.

Agents, disease, human, and Environment

Judging from the ecological angle, there are three factors that can lead to an illness, disability, incapacity, or death in humans. Three factors were referred to as ecological or epidemiological triad consisting of agents of disease, humans, and environment. Under normal condition, these three components, or in other words, the people are called illness at the current state of dynamic equilibrium is disturbed, for example, when the quality of the environment decreases to a certain extent, disease agents can easily fit into the human body and cause illness.


The natural history of the disease is the natural history of the disease in humans comprising:

Phase Prepatogenesis. 

In this phase began disturbances balance between disease agents, humans, and the environment. Here, the environmental conditions is more favorable for disease agents and adverse to human. For example, air pollution due to burning of forests by farming in the dry season would cause heavy smoke or smog that beneficial for disease agents and detrimental to human.

Phase Pathogenesis

If the environmental conditions that favor disease agents is ongoing in a long time, there will be symptoms and signs of clinical signs. Humans become ill which can then be cured or the disease goes on cause of disability, chronic disability, or death.

The journey of a disease occur started a disturbance of balance between disease agent, host, and environment until the occurrence of a disease.

Disease Agents

Disease agents can be either animate or inanimate and mechanical factors. Sometimes the cause for a particular disease is not known, for example, the cause of peptic ulcer disease, coronary heart disease, and others. Disease agents can be classified into five groups, among others:
  • Biological agents. Example: viruses, bacteria, fungi, ricketsiae, protozoans, and metazoans.
  • Agents nutrients. Example: proteins, fats, carbohidrat, vitamins, minerals, and water.
  • Physical agents'. Example: heat, radiation, · cold, humidity, pressure, light, and noise.
  • Chemical agents. Chemical agents can be endogenous, such as acidosis, diabetes (hyperglycemia), and uremia or exogenous nature, such as chemicals, allergens, gases, dust, and others. 
  • Mechanical agents. Friction, collisions, or blows that can cause damage to the body tissues of the host (host).

Human (Host)

The human factor is very complex in the disease process. These factors depend on the characteristics of each individual, among others:
  • Age. Age causes the difference in the illness, such as smallpox disease in childhood, cancer in middle age, and atherosclerotic disease in the elderly.
  • Gender (sex). The frequency of the disease in males is higher than the frequency of the disease in women. Meanwhile, certain diseases, such as the risk of pregnancy and childbirth only found in women, whereas prostatic hypertrophy disease was only found in men.
  • Race. The relationship between race and disease relies on the development of customs and cultures in addition there is a disease that is only found in certain races such as sickle-cell anemia in the Negro race.
  • Genetic. There are certain diseases that inherited hereditary, such as mongolism, phenylketonuria, color blindness, hemophilia, and others.
  • Work. Employment status is closely linked to occupational diseases, such as poisoning, work accidents, silicosis, asbestosis, and others.
  • Nutrition. Malnutrition facilitate someone suffering from infectious diseases, such as Tuberculosis and nutrition disorders such as obesity, high cholesterol, and others.
  • Immune Status. The reaction of the body against disease depends on the immune status of previously owned such as immunity to viral diseases are durable and last a lifetime.


There are some traditions that can cause disease. For example, the habit of eating raw fish can cause disease · heartworms.


Drinking alcohol, drugs, and smoking can cause health related problems.


Psychological factors such as stress can cause hypertension, peptic ulcer, depression, insomnia, and others.


Human environment basically consists of two parts, internal and external. Internal environment is a dynamic and balanced state called homeostasis, while the external environment is an environment outside the human body consists of three components:

Physical Environment

The physical environment is abiotic or inanimate objects such as water, air, soil, weather, food, housing, heat, light, radiation, and others. The physical environment interacts constantly with humans throughout time and time and plays an important role in the occurrence of the disease in the community. For example, the shortage of water supply, especially in the dry season can cause diarrhea everywhere.

Biological environment

Biological environment is biotic or living objects, such as plants, animals, viruses, bacteria, fungi, parasites, insects, and others that can act as agents of disease, the reservoir of infection, disease vectors, and host intermediates. Human relationship with the biological environment is dynamic and in certain circumstances when there is an imbalance between the relationship, people will become ill.

Social environment

Social environment such as culture, customs, habits, beliefs, religion, attitudes, standards and lifestyles, work, social life, social and political organizations. Humans are influenced by the social environment through various media such as radio, TV, press, art, literature, stories, songs, and so on. If human can not adapt itself to the social environment, there would be a conflict of psychiatric and psychosomatic cause symptoms such as stress, insomnia, depression, and others