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CSEC Biology: Disease

Disease refers to any condition that impairs the normal function of an organism's cells, tissues or organs that results in a decrease in the health of the organism. We've all heard about all sorts of diseases, from chikungunya to sickle cell and from dysentery to our brand-new COVID-19. However, all of the diseases we currently know of can be divided into four main categories:

  • Pathogenic diseases

  • Deficiency diseases

  • Hereditary diseases

  • Physiological diseases

Pathogenic Diseases (Communicable Diseases)

These diseases are caused by harmful microorganisms called pathogens. These pathogens are usually parasites that cause disease in their hosts. These microorganisms can be viruses, bacteria, fungi or protozoans. For example, gonorrhoea is caused by the bacterium Neisseria gonnorrhoeae and COVID-19 (Lord save us) is caused by the SARS-CoV-2 virus.

Other examples of pathogenic diseases include AIDS, the common cold, dengue (caused by viruses), syphilis, tuberculosis, cholera (caused by bacteria), athlete's foot, ringworm (caused by fungi), malaria and dysentery (amoebic) (caused by protozoans).

(Note: the graphic above shows prions as well, infectious proteins that have folded abnormally into a structure capable of causing disease by causing other proteins to fold in the same abnormal way. You don't have to know this for the CSEC Biology course)


With such a wide variety of pathogenic diseases, it follows that there are several ways to treat them.

The symptoms of pathogenic diseases are usually treated with certain drugs, such as aspirin for pain relief. The roots of the problem (the pathogens) are killed using specific drugs like antibiotics (to kill bacteria), antiviral agents (to kill viruses) and antifungal agents (to kill fungi).

In certain cases, the person is injected with ready-made antibodies to kill pathogens before they can infect the body, such as with tetanus- a tetanus shot is administered for a tetanus prone wound.


However, if pathogenic diseases are not controlled, they can cause widespread damage to human lives and livelihoods by infecting large populations. Business will slow due to workers infected and unable to work, reducing productivity, and as a result, the economy will recede. Outbreaks of pathogenic diseases can put large strains on health facilities as more people seek treatment, increasing the likelihood that some of the infected do not get access to the treatment needed.

I don't need to tell you this though, because if you are reading this, you are living (or have lived, hopefully) through a pandemic, and you understand the economic and social effects and reduction in living standards that can result from an outbreak.

So, it goes without saying that 'prevention is better than cure' (yes, even now). Pathogenic diseases can be controlled by:

  1. Quarantining infected individuals

  2. Ensuring that entire populations are vaccinated using immunization programmes

  3. Eradicating disease vectors (organisms that carry pathogens in or on their bodies)

  4. Improve sanitation standards and sewage treatment

  5. Implement public health education programmes

  6. Practice good hygiene and sanitary food preparation tenchniques

  7. Utilize condoms during intercourse to prevent STI transmission

  8. Ensure drinking water is properly treated

NB: Pathogenic diseases are the only communicable diseases, as they are contagious and can be passed from person to person. All other types of diseases are non-communicable.


Deficiency Diseases

These are diseases caused by the shortage or lack of a particular nutrient or mineral in the diet. As you know, the body requires certain nutrients and minerals in order to function properly. If there is an insufficient amount of these nutrients in the diet, the body will exhibit certain conditions known as deficiency diseases.

For example, scurvy is caused by a lack of vitamin C, goitre is caused by a lack of iodine, anaemia is caused by a lack of iron, beri beri is caused by a lack of vitamin B, and kwashiokor is caused by a lack of protein.


These diseases can be treated by consuming a diet consisting of foods rich in the missing nutrient, or by taking dietary supplements of the missing nutrient.

Preventing deficiency diseases is just as simple:

  1. Improve population nutrition

  2. Set up public health education programmes which focus on nutrients and balanced diets


Hereditary Diseases

Hereditary diseases are conditions passed between generations of offspring through an abnormal gene (allele). Examples of these diseases include sickle cell anaemia, Huntington's disease, haemochromatosis, Marfan syndrome and cystic fibrosis.

These diseases are tied directly to a person's genetic makeup (genotype), so treatments are few and far between. Drugs are used to relieve symptoms of these diseases, but no cure currently exists. However, a promising development in genetics a few years ago known as CRISPR (Clustered Regularly Interspersed Palindromic Repeats) is likely to increase options for those suffering from hereditary diseases. CRISPR is a gene editing system based on the immune responses of prokaryotes that can modify a target gene in an organism. In March 2020, a CRISPR treatment for hereditary blindness was tested in the body for the first time (and showed improvements in vision)- so there is promise for genetic treatments/cures of these illnesses soon.


Prevention of hereditary diseases is quite difficult, and is limited to avoiding situations which exacerbate (worsen) symptoms and seek counselling to predict the chance that offspring will develop the disease.


Physiological Diseases

These diseases are caused by the malfunctioning of body cells, an organ or group of organs in the body over time. For example: diabetes (caused by malfunction of the pancreas in insulin production), hypertension (caused by several lifestyle choices), cancer (caused by malfunction of body cells causing aberrant cells to reproduce uncontrollably) and Alzheimer's Disease (likely caused by the build-up of protein 'plaques' and 'tangles' around brain cells).


These diseases are treated with drugs to relieve symptoms as they develop. Some physiological diseases require particular treatment, like cancer, which can be treated with radiotherapy or chemotherapy to kill tumours.

Diabetes and hypertension can both be treated with exercise and healthy eating habits to maintain fitness and improve circulation.


Prevention of these diseases can be achieved by eating a balanced, healthy diet, exercising regularly and adopting a lifestyle that reduced exposure to risk factors (i.e. avoiding smoking, excessive alcohol consumption, and reducing obesity)


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