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From time immemorial, mankind has been plagued by many life-threatening infectious diseases. There is a long historical relationship between humans and diseases, especially infectious diseases. This relationship dates back to the pre-agricultural period, and if current research on the emergence of diseases such as tuberculosis is correct, before humans migrated out of Africa. Historically, epidemics have affected the history of mankind in countless ways: demographically, culturally, politically, financially, and biologically. There is always epidemic outbreak throughout human history (about every one hundred years). This is true today as always.The World Health Organization (WHO) defines an epidemic as the occurrence of an illness, specific health-related behaviors, or other health-related events beyond the normal expectation in a community or region. The number of people with the disease that indicates an epidemic varies according to the agent, size and type of population exposed to the pathogen, previous exposure or lack of exposure to the disease, and time and place of occurrence. A pandemic is when an epidemic occurs worldwide or over a very large area and crosses international borders and usually affects a large number of people. The classical definition includes nothing about population immunity, virology or disease severity. This definition implied that pandemics occur every year in each of the southern and northern hemispheres temperate, as seasonal epidemics cross international boundaries and affect a large number of people. although, seasonal epidemics are not considered as pandemics.According to the Centers for Disease Control and Prevention (CDC), an epidemic is an abrupt increase in the number of cases more often than is normally expected in that population and region, and a pandemic is an epidemic that occurs in several countries or continents and usually affects a large number of people. Epidemics take place when there is a sufficient number of pathog