Let me send your mind back to that uncomfortable time you caught that cold or had that terrible fever and vomited.Though this doesn’t give the whole picture, these memories give a slight glimpse of what a disease is.

In times past, man has always found it difficult to comprehend what a disease is, but we like to think that we know what it is when we see one. In addition, based on the definition of health provided by the World Health Organization, it is basic to say disease is the opposite of health.

Health is “a state of complete physical, mental and social wellbeing, not merely the absence of disease or infirmity.” (WHO, 1946).

However, a disease as defined by Merriam Webster Dictionary is any deviation from or interruption of the normal structure or function of any body part, organ or system that is often manifested by a characteristic set of symptoms and signs and whose etiology (cause), pathology (disease process), and prognosis (predicted outcome of disease) may be known or unknown.

Furthermore, there is a broad scope of meaning to what a disease is in humans. This normally refers to any condition causing pain, dysfunction, distress, social problems or death to the person involved or afflicted or similar problems for those in contact with the person.

This brings us to the various forms to which a disease can take.

Disease and its similar terms

Before we can begin to unravel the forms of diseases, it is best to understand a couple of terms which are normally used interchangeably.

  • Disease:

    A condition that impairs normal functioning of the body processes. This includes the basic processes of a living organism (nutrition, respiration, excretion, reproduction, movement, stimuli (sensitivity), growth). In addition, it is a term not only used for infectious diseases which involves microbial pathogens (bacteria, fungi, viruses, multicellular organisms and so on), it is used for non-infectious diseases portrayed in various forms such as (cancer, systemic diseases and genetic diseases).

  • Disorder:

    A disturbance or abnormality in function, mental status, physique, genotype (genetic structure), emotional and behavioral state. Primarily used to identify physical disorders not caused by infectious pathogens.

  • Morbidity:

    A diseased state or a decline in health due to any cause. In addition, the term ‘morbidity rate’ refers to the incidence or prevalence of a disease or medical condition which often assists in health care insurance plans.

  • Sickness or Illness:

    This refers to patients’ personal experience of a disease. In actual sense, it is possible for one to have a disease without being sick, an asymptomatic (without symptoms of disease) state. On the other hand, a person can also be ill without having a disease, such as a person feeling unwell due to an embarrassing moment in their lives. Illness can include signs such as depression, loss of appetite, fatigue, sleepiness and loss of concentration.

Disease can be classified in many ways including but not limited to, cause, by the body system it affects, by the stage at which the disease is, by the extent of the disease and many other ways. We will however briefly talk about a couple of these.


Disease can additionally be classified based on its cause into the following:

  • Acquired disease:

Present during a point in one’s life not present already at birth such as Gonorrhea  and Diabetes which is normally acquired due to lifestyle.

  • Congenital disease:

Present at birth due to a genetic disorder, inheritance or infectious disease transmission from mother to child.

  • Genetic disease:

Caused by genetic disorders in genotype (genetic structure).An example is Sickle Cell Disease

  • Inherited or Hereditary disease:

Caused by genetic disorders that transcend in families.

  • Iatrogenic disease:

Caused by medical intervention as an adverse effect of treatment or poor prognosis.

  • Idiopathic disease:

Diseases with an unknown cause or source. Progress in medicine has led to the loss of this status on particular diseases such as diabetes and many others. However, actual causes have not been identified for most diseases in this category only associating factors have been identified over the course of time.

  • Incurable disease:

Diseases that have no cure. An incurable disease is not a terminal disease however it can be treated to reduce the impact of the disease on the patient’s quality of life.

  • Primary disease:

Diseases that arise spontaneously without any association to a previous disease. These can normally cause secondary diseases if not treated properly.

  • Secondary disease:

A complication of a primary disease or a disease that is a complication of an underlying cause. An infection with a virus is a primary infectious disease but the presence of a bacterial infection due to a weakened immune system is a secondary infectious disease.

  • Terminal disease:

Disease with death as an expected inevitable outcome.


  • Mental Diseases:

Broad label for illnesses that include emotional instability, behavioral instability, cognitive impairment. Depression and anxiety disorders are a few specific conditions known to fall under this category. The cause could be pathological (anatomical, chemical or genetic disorder) or psychological (trauma or conflict). It affects and impairs the patient’s ability to work or study and can destroy interpersonal relationships.

  • Organic Diseases:

Diseases characterized by a physical change in the tissue or organ of the body. It normally includes emotional disorders due to changes in physical structure or functioning of the body.


  • Acute Disease:

Disease with a short duration of symptoms and sudden onset with a clinical course of < 1 month.

  • Chronic Disease:

Disease with a long duration of symptoms and progressive clinical course of at least six months

  • Clinical Disease:

Disease that produces characteristic signs and symptoms of the disease.

  • Progressive Disease:

Disease which has a worsening clinical course until death, leading to serious disability or organ failure.

  • Refractory Disease:

Disease that resists treatment, more than the normal for a specific disease in question.

  • Sub-clinical Disease:

A disease stage before symptoms are noticed, also known as the silent stage.

  • Terminal Phase:

The stage between the previous disease process and active period of death. It’s normally seen in progressive disease that are terminal.


  • Localized Disease:

Disease affecting only a single part of the body.

  • Disseminated Disease:

Disease affecting other parts of the body.

  • Systemic Disease:

Disease affecting the entire body.


The origin of a disease is key in its treatment, whether it be based on infection by microbial pathogenic organisms through contaminated food and water or based on non-infectious causes such as genetic disorders, cancers and the rest. The causes of diseases include the following:

  • Airborne Causes:

Pathogens of a disease transmitted through air.

  • Food-borne Causes:

Diseases resulting from consumption of contaminated food with microbial pathogenic organisms

  • Infectious Causes:

Diseases resulting from transmissible or communicable infections. Infections that are spread from one person to another via sexual contact, physical contact or use contaminated items.

  • Lifestyle Causes:

Behavioral choices affecting lifestyle habits such as sedentary (inactive) lifestyle or unhealthy lifestyle in nutrition such as diet high in refined sugar, alcoholic beverages and fats and hygiene such as poor oral hygiene and poor genital hygiene.

  • Non-communicable Causes:

Diseases that cannot be transmissible meaning it cannot be spread from one person to another directly.


Most of the diseases in our world today can be prevented through ensuring the following:

-Proper sanitation in our homes and environs to reduce the presence of microbial pathogenic organisms.

-Proper nutrition to improve and boost our immune system against microbial pathogenic organisms

-Adequate exercise to ensure normal functioning and maintenance of the tissues and organs of the body.

-Vaccinations to boost our immunity against viral infections that can lead to terminal illness.

Always visit the hospital when you feel unwell as that is the most definitive way to be sure and receive the appropriate treatment in the incident that you are sick.