Eradication literally means to ‘tear out by roots’. Eradication of disease implies termination of all transmission of infection by extermination of the causative agent. Eradication is an absolute process but not a relative goal. It is all or none phenomenon. The eradication of disease refers to cessation of infection and disease from the whole world.
Today, small pox is the only disease that has been eradicated. So far no strategy for global eradication of any other disease has been developed. Every disease is unique with its own epidemiological characteristics and specific strategies for control. Recently three diseases are listed as candidates for global eradication
Polio
Measles
Dracunculiasis
Efforts towards eradication of polio are greater than others
Once morbidity of the disease reaches very low level, a residual infection always persists in the population leading to a state of equilibrium between the agent, host and environmental components of the disease process. In such a situation there are always hidden foci of infection, unrecognized methods of transmission, resistance of the vector or organism which may flare up when the agent-host-environment equilibrium is disturbed.