Through the ancient plaque till the recent human immunodeficiency virus all have played a pivotal role in developing diseased condition in human beings. It could be the result of expansion in human population as well as inventions of new strains of infectious agents. Understanding the nature of infectious agent / pathogen is very important to prevent and control the infection at population level. Communicable diseases continue to pose a threat for not only the third world but also South Eastern Europe countries. Addition of new infectious agents with old diseases are reappearing and developing drastic effects on human population. These diseases include tuberculosis, West Neil fever, human immunodeficiency virus and other sexually transmitted diseases. Much of this evolving disease burden began in the early 1990s. TheÂ World Health OrganizationÂ collects information on global deaths byÂ International Classification of Disease (ICD) code categories. The list includes the top infectious disease killers which caused more than 100,000 deaths in 2002.