An infection is the invasion of any organism’s tissue by disease causing agents such as bacteria, viruses, fungi or parasites etc. These disease causing agents are also called as infectious agents [1-5]. Infectious disease is also known as communicable disease. Most, not all, of the infectious agents are micro-organisms. These micro-organisms are microscopic living organisms that can be seen through microscope. These may be single or multicellular and are very diverse. Many micro-organisms live in and on our bodies. These are normally harmless or even helpful, but under certain conditions, some organisms may cause disease [5-10].
Some infectious diseases can be passed from person to person. Some are transmitted by bites from insects or animals. And others are acquired by ingesting contaminated food or water or being exposed to organisms in the environment [11-13]. The Signs and symptoms vary depending on the organism causing the infection. Most of the developing nations are prone to infectious diseases [14].
Major infectious diseases include bacterial and viral diseases. In this article some of the most common bacterial and viral diseases are discussed [15,16].