Diseases Spread From Person To Person. An infection occurs when germs enter the body, increase in number, and cause a reaction of the body. Infectious diseases can be caused by many pathogens, including bacteria, viruses, fungi, and parasites that may cause illness and disease.

They are of long duration and generally slow progression. Pathogens such as viruses, bacteria, and fungi cause these diseases. A disease resulting from the presence and activity of a pathogenic microbial agent.