Common Human Diseases

Disease is defined as a condition of disturbed or deranged functioning of one or more organs or organ systems, caused by infection, a defective diet, or heredity. Broadly, all human diseases fall into two categories: congenital diseases, present from birth (caused by a genetic abnormality or metabolic disorder, often permanent though modern gene therapy and enzyme-replacement therapy can now cure some), and acquired diseases, which develop after birth.

Acquired diseases are further divided into: communicable (infectious) diseases, which are transmitted from an infected person to a healthy one, directly or indirectly, and are caused by pathogens such as viruses, bacteria, fungi and helminth (parasitic) worms — malaria and the other diseases covered in this chapter belong to this group; and non-communicable (non-infectious) diseases, which cannot be transmitted person to person, such as cancer and deficiency diseases. …