Infection. 

This is the invasion of disease-causing microorganisms into the body. Infections normally lead to diseases.


Disease. 

This is the disturbance of the normal state of the body. It is a disordered state of an organ or organism.


Classification of diseases.

Diseases are classified as:

1.      Infectious (communicable) diseases.

2.      Non-infectious (non-communicable) diseases.


Infectious (communicable) diseases.

These are diseases which can be transmitted from one person to another person. Communicable diseases are normally caused by microorganisms like viruses, bacteria, fungi and protozoa, etc

Examples of infectious diseases include: malaria, typhoid, tuberculosis, cholera, gonorrhoea, syphilis, ebola, AIDS, chlamydia, etc.


Many of the infectious diseases are transmitted by a way of:

·         Droplet of liquid

·         Air

·         Food or water

·         Sexual intercourse

·         Touch or contact e.g. ringworm

·         An intermediate organism called a vector e.g. malaria by mosquito and bubonic plague by rat flea.

 

Diseases causing microorganisms can enter the body through mouth, nose, skin, vagina, anus, penis, ears, eyes and open wounds.

 


Infectious diseases can be:

a.       Epidemic disease - a disease that affects a larger number of people in a short period of time in a region for example, cholera, meningitis, bubonic plague, rift valley fever (RVF), tuberculosis, etc. 

b.      Pandemic disease - a communicable disease which is wide spread over a country continent or the whole world, for example HIV/AIDS, etc. 

c.       Endemic disease - a communicable disease which occurs in an area continuously for example, bilharzia, sexually transmitted diseases (STDs), malaria (an endemic disease in tropical regions) and cholera (endemic in Asia).

 

Non- infectious (non-communicable) diseases.

These are diseases which can not be transmitted from one person to another. 

Examples of non-communicable diseases include:

 

Environmental diseases e.g.:

1.      Lung cancer

2.      Asbestosis 

3.      Asthma

4.      Coronary (heart) diseases 

5.      Alcoholism

 


Deficiency diseases.

These diseases are due to lack of certain nutrients in the diet. They may be due to lack of one of the main food groups e.g.:

1.      Kwashiorkor: lack of protein

2.      Marasmus: lack of both carbohydrate and proteins

3.      Night blindness: lack of Vitamin A

4.      Beriberi: lack of Vitamin B1

5.      Scurvy: lack of Vitamin C

6.      Rickets: lack of Vitamin D, calcium, and phosphorous

7.      Anaemia: lack of iron

8.      Goitre: lack of iodine

9.      Excessive bleeding (haemophilia): lack of Vitamin K

 

Genetic and congenital disorders e.g. 

1.      Colour blindness 

2.      Haemophilia

3.      Sickle cell anaemia 

4.      Albinism

5.      Down‟s syndrome

6.      Klinefelter's syndrome

7.      Turner's syndrome

 


Ageing and degenerative diseases e.g.

1.      Long sightedness due to weakening of eye muscles

2.      Arteriosclerosis (hardening of arteries)

3.      Arthritis – ageing of joint and bone tissues

 


Mental illness e.g.

1.      Schizophrenia

2.      Senile dementia

3.      Depression

 


Hormonal diseases e.g.

1.      Diabetes mellitus

2.      Diabetes insipidus 

3.      Cretinism