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Health and Disease

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Biology

Defining and categorising health and disease is not as simple as it may sound. Many different definitions and categories exist, and in this article, we will explore some of these. Let’s get into it.

What is health?

There are many different definitions of the term ‘health’. One definition describes health as an individual being “free from disease or an impairment”.

However, issues arise with this definition. Firstly, some people may have a disease or abnormality but feel perfectly well and live normally. For example, many people have peptic ulcers and other infections but do not experience any problems. They may not even know they have the disease and do not seek treatment.

Another issue with this definition is that while someone may be in perfect health today, they could be found to be ill tomorrow through a novel (new) medical diagnostic method. This inconsistency renders the definition problematic.

A more appropriate definition of health is:

Health: The state of complete physical, mental and social well-being.

This definition considers the individual's physical health and the psychological and social aspects of an individual’s well-being.

What is disease?

Some may define the term ‘disease’ as the opposite of health, but a more accurate description of disease is as follows:

Disease: A state of illness or sickness that produces various signs or symptoms.

Disease is not necessarily the direct result of physical injury but rather a disorder of the body or brain’s biochemistry, physiology and/or anatomy.

Diseases can be either acute or chronic. An acute disease is any disease with a rapid onset with fast-changing symptoms and is short-lived. It can typically be cured with treatment, such as medication or surgery. An example of acute disease is appendicitis.

However, a chronic disease is any disease that lasts for an extended period and requires ongoing medical treatment. It cannot typically be cured; however, medication or other procedures can help to manage some of the symptoms. An example of a chronic disease is terminal cancer.

Categories of disease

Diseases can be classified into different categories, depending on the nature of the disease and how it affects the body. They can also be classified regarding the tissue they affect, their cause and other reasons. Each classification serves to help us understand a specific aspect of a disease and relate it to similar diseases according to said classification.

Table 1. Example classification of diseases.

Category

Cause

Description

Examples

Infectious

Infection from a pathogen

Infection resulting from a pathogen that may be transmitted from a source, e.g., animal

Covid-19;

Malaria

Degenerative

Causes could be genetic, lifestyle or infectious.

Any disease that causes a gradual decline of size or function of an organ over time. This is often observable in a patient, e.g., gradual mental decline for diseases affecting the brain.

Alzheimer’s disease;

osteoarthritis

Deficiency

Not receiving enough nutrients in your diet.

Any nutritional disease caused by an inadequate diet results in starvation

Scurvy

Inherited

Genetic cause where specific genes are faulty.

Parents may pass faulty genes to their children, causing the disease to develop in the child.

Cystic fibrosis;

sickle-cell anaemia

Physical

Physical damage to the body.

Any disease that causes permanent or temporary damage to any tissues, organs or other structures of the body

Leprosy;

autoimmune diseases;

cancer

Mental

Changes in brain chemistry; mental or physical trauma

Any disease affecting the mind.

Schizophrenia;

depression;

anorexia

Diseases may alternatively be categorised simply into two categories; communicable diseases and non-communicable diseases.

Communicable diseases can be passed on from one organism to another. They include all infectious diseases since infective pathogens can be passed on between organisms.

Non-communicable diseases cannot be passed on from one organism to another, including every disease except infectious diseases.

Interactions between different types of diseases

Sometimes, communicable diseases can cause or increase the likelihood of developing a non-communicable disease.

Take HIV, for example. HIV, which stands for Human Immunodeficiency Virus, is a virus that attacks the immune system, causing AIDS - a communicable disease. The virus infects and replicates inside immune cells in the blood. The virus particles eventually burst the cells, killing them in the process. Thus, the new virus particles can infect more immune cells and weaken the immune system quickly. This makes it easier for other diseases to develop in the patient; for example, AIDS patients are more likely to develop a type of skin cancer called Kaposi’s sarcoma, caused by the Epstein-Barr virus, or develop cancer (a non-communicable disease) because the immune system is unable to fight the growth of cells as it would if it were in healthy conditions.

Health and disease statistics

Now that we’ve covered the concepts of health and disease, let’s look at how statistics can provide meaningful information about health and disease. Learn more about health statistics in our article here.

Heath statistics is the science of collecting, summarising and interpreting data on health and disease in populations.

Everything we know about the patterns of health and disease in populations is due to statistics.

Three indicators can provide scientists and health professionals with crucial information about how a disease is progressing in a population, these are:

  • Incidence – measures the number of new cases of the disease within a given period

  • Prevalence – measures the number of people with the disease in a population

  • Mortality – measures the number of people who have died from the disease

The World Health Organisation (WHO) is an inter-governmental body that collects health statistics and data globally. While specific governments assess disease patterns within their own country, the WHO assesses disease patterns across all countries.

A significant role of the WHO is to monitor infectious diseases on a global scale. They collect data from individual countries to plan and implement strategies to combat infectious diseases, such as providing free vaccinations to regions urgently requiring them.

Data gathered by the WHO show significant geographical differences in the spread of infectious diseases. Infectious and parasitic diseases are highly prevalent in Africa and South Asia, while the rest of the world has comparatively lower infection levels. Read our Health Statistics article to learn more about why these differences exist.

Health and Disease - Key takeaways

  • There are many definitions of health.

  • Health is the state of complete physical, mental and social well-being

  • Disease is a state of illness or sickness that produces specific signs or symptoms

  • Diseases can be classified according to different parameters, for example, "communicable vs non-communicable diseases."

Health and Disease

Types of diseases include: infectious diseases, deficiency diseases, inherited diseases, physical diseases, self-inflicted, degenerative diseases and mental diseases. 

Disease can be defined as a state of illness or sickness that produces specific signs or symptoms. 

Health is the state of complete physical, mental and social well-being, while disease is the state of illness or sickness that produces specific signs or symptoms

Ischaemic heart disease, 
Stroke, 
Chronic Obstructive Pulmonary Disease (COPD) 
Lower respiratory infections, 
Neonatal disorders, 
Trachea, bronchus and lung cancers
Diabetes mellitus
Alzheimer’s disease and other dementias
Diarrheal diseases
Tuberculosis (TB)
Liver cirrhosis

Disease can have various causes, such as genetic causes or environmental causes or lifestyle causes.  

Final Health and Disease Quiz

Question

Define the term epidemiology.

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Answer

Epidemiology is the scientific study of the incidence (occurrence), distribution (spread or patterns) and control of diseases and risk factors in populations.

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Question

An endemic can be described as a disease that has spread to other continents. True or false?

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Answer

False.

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Question

The coronavirus disease outbreak was a pandemic. True or false?


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Answer

True.

Show question

Question

Which major governing body collects global data on health and disease?


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Answer

WHO

Show question

Question

Cardiovascular disease is higher in the developing world than in the developed world. True or false?


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Answer

False.

Show question

Question

Define the term ‘disease’.


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Answer

The science of collecting, summarising and interpreting data on health and disease in populations.

Show question

Question

Epidemiologists assess three indicators; these are incidence, ________, and mortality.


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Answer

Prevalence 

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Question

A rapid rise in obesity rates can not be considered an epidemic because epidemics only describe infectious diseases, such as COVID-19. True or false?


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Answer

False. Endemics, epidemics and pandemics can describe any disease that is rapidly rising in a population.

Show question

Question

Processed food can contain chemicals that increase the risk of cardiovascular disease. True or false?


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Answer

True.

Show question

Question

The diets of developing countries tend to include foods high in fats and salt, and food that is processed, whereas diets of developed countries tend to include mostly fruits and vegetables. True or false?


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Answer

False, developed countries have diets that are high in fats and salt, as well as processed food. Developing countries have diets mostly based on fresh fruits and vegetables since subsistence farming is common.

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Question

Obesity is a major risk factor for various diseases, such as cancer, heart disease and stroke. True or false?


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Answer

True.

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Question

Developing countries tend to have more extensive public health education than developed countries. True or false?


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Answer

False.

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Question

What is meant by the term ‘subsistence farmer’?

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Answer

People who grow crops and livestock to feed themselves and their families. They do not do it for economic gain.

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Question

Infectious and parasitic diseases are more prevalent in Europe than South Asia. True or false?


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Answer

False, Europe has one of the lowest prevalences for infectious and parisistic diseases.

Show question

Question

Infectious and parasitic diseases are more prevalent in Africa than South Asia. True or false?


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Answer

True, Africa has the highest prevalence for infectious and parasitic diseases.

Show question

Question

 Why is it innacurate to define health as simply being free from disease or impairment?

Show answer

Answer

Firstly, some people may have a disease or abnormality but may feel perfectly well and live normally. For example, many people have peptic ulcers and other infections but do not experience any problems. They may not even know they have the disease and do not seek treatment. 


Another issue with this definition is that while someone may be in perfect health today, they could be found to be ill tomorrow through a novel (new) medical diagnostic method. This inconsistency renders the definition problematic.   

Show question

Question

What is an accurate definition of health?


Show answer

Answer

The state of complete physical, mental and social well-being

Show question

Question

What is an acute disease?


Show answer

Answer

any disease that has a rapid onset with fast changing symptoms, while being short in duration

Show question

Question

What is a chronic disease?


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Answer

any disease that lasts for an extended period of time and requires ongoing medical treatment. It cannot typically be cured; however, medication or other procedures can help to manage some of the symptoms.

Show question

Question

Give two examples of a degenerative disease.


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Answer

Alzheimer’s disease, osteoarthritis

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Question

An acute disease is any disease that lasts for an extended period of time, requiring ongoing medical treatment. True or false?


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Answer

False, an acute disease is any disease that has a rapid onset with fast changing symptoms, while being short in duration.

Show question

Question

Cystic fibrosis falls into which category of disease? Choose one.

A - Mental

B - Inherited

C - Infectious

D - Self-inflicted


Show answer

Answer

B

Show question

Question

 Cardiovascular disease falls into which category of disease? Choose one.

A - Infectious

B - Inherited

C - Deficiency

D - Self-inflicted

Show answer

Answer

D

Show question

Question

Scurvy falls into which category of disease? Choose one.

A - Infectious

B - Degenerative

C - Deficiency

D - Mental

Show answer

Answer

C

Show question

Question

A patient’s brain volume has reduced gradually over the course of a year. Their mental capacity has also declined. What category of disease can this be classed in?

A - Degenerative

B - Infectious

C - Deficiency

D - Inherited

Show answer

Answer

A

Show question

Question

What is the difference between a degenerative disease affecting the brain and a mental disease?


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Answer

A degenerative disease affecting the brain would cause a gradual decline in size or function of the brain, such as in Alzheimer’s disease. This is often observable in Alzheimer’s patients where memory and mental abilities are severely affected. Mental diseases, in contrast, are diseases of the mind. They often result due to traumatic experiences or changes in brain chemistry. Examples include depression or schizophrenia.

Show question

Question

Covid-19 falls into which category of disease? Choose one.

A - Physical

B - Inherited

C - Deficiency

D - Infectious

Show answer

Answer

D

Show question

Question

 Leukaemia is a form of blood cancer. Leukaemia falls into which category of disease? Choose one.

A - Infectious

B - Deficiency

C - Physical

D - Mental

Show answer

Answer

C

Show question

Question

Fill in the blank. HIV stands for Human ____________ Virus.


Show answer

Answer

Immunodeficiency

Show question

Question

 Diabetes Mellitus Type 1 can be considered as a communicable disease. True or false?


Show answer

Answer

False, it is a non-communicable disease

Show question

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