Infectious diseases are worldwide com- mon illnesses caused by the entry of harm- ful agents, such as viruses, bacteria, fungi, and parasites, into the body. Some infectious diseases are contagious (or communicable), that is, spread from one person to another while other infectious diseases can be seen due to the spread by germs carried through the air, water, food, soil, or by vectors (like biting insects) or by animals. The most com- mon infectious diseases caused by viruses are the flu (influenza), hepatitis, and HIV. Ear- ly detection of infectious diseases and rapid and accurate identification of the underlying agent plays a crucial role in all prevention and treatment strategies.
