Infectious diseases are caused by the entry and manifestation of pathogenic microbes, viz. bacteria and viruses. Most infectious diseases need a carrier to enter into human body system. These carriers may be lice, houseflies, mosquitoes, animals etc. Once inside, these pathogens multiply in numbers and manipulate the normal functioning of the body tissues thereby causing diseases. Cholera, Malaria, Typhoid, Common cold, Flu are some of the most common infectious or communicable diseases that spread from person to person or through water, air and food.