Describe the various levels of causes of disease.

These diseases involve temporary or permanent damage to the body and include all the other categories except mental disease where there is no sign of physical damage to the brain. An example would be leprosy.

Pathogens - They are organisms living in or on our bodies, causing disease. Infectious diseases are caused by pathogens such as viruses, bacteria, fungi, protoctists, worms and insects, which can be transmitted from person to person. This may be via normal social contact - for example, chicken pox, or via food and water, sexual contact or an animal bite. Carriers are people who can transmit the pathogen but do not have the disease symptoms.

Non-infectious diseases - These are all diseases, which are not caused by pathogens and cannot be passed on by physical contact. An example would be sickle cell anaemia.

Deficiency diseases - These are nutritional diseases caused by an inadequate or unbalanced diet. One or more essential nutrient is missing or in short supply - for example, a shortage of Vitamin C causes scurvy.