Infectious diseases are disorders caused by organisms — such as bacteria, viruses, fungi or parasites. Many organisms live in and on our bodies. They are normally harmless or even helpful. However, under certain conditions, some organisms may cause disease.
Some infectious diseases can be passed from person to person. Some are transmitted by insects or other animals. You may also get others by consuming contaminated food or water or being exposed to organisms in the environment.
Signs and symptoms vary depending on the organism causing the infection, but often include fever and fatigue. Mild infections may respond to rest and home remedies, while some life-threatening infections may need hospitalization.
A communicable disease is an infectious disease that is contagious and which can be transmitted from one source to another by infectious bacteria or viral organisms.
Sources: WHO, Mayo Clinic