Health and Disease

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 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.

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.

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.