Disease eradication occurs when the incidences of infection of a given infection disease around the world are reduced to zero. After eradication, no human intervention is necessary to prevent others from coming down with the disease. If any intervention is still necessary, true eradication has not yet occurred. Eradication is an intentional process; health professionals around the world collaborate and make focused attempts to reduce the incidences of a disease to nothing so it cannot affect others ever again. Disease eradication is often confused with disease elimination, in which incidences of a disease in one particular area are reduced to zero.
Disease eradication is an incredibly difficult process given the pervasive and rapidly-replicating nature of most disease-causing agents. To date, the only disease that has ever been successfully eradicated from the Earth is smallpox, an incredibly deadly viral infection unique to humans. Highly effective vaccination methods protected humans from contracting the virus. Without hosts to infect, the virus could not sustain itself and the global incidences of smallpox dropped to zero. Aside from isolated samples maintained in carefully controlled labs for research purposes, the viruses that cause smallpox have been successfully and completely eradicated.
There are three main factors that must be present in order for a disease to be considered eradicable. For disease eradication to occur, there must be a way to cease the transmission of the disease between humans so the infection cannot freely spread from one person to another. There must also be an accurate way to diagnose individuals; eradication cannot be verified if proper diagnostic techniques do not exist. Finally, it must be a human disease that cannot survive in other animals or in the external environment, as it is simply not viable to eradicate a disease that can exist in any number of organisms or in any number of external locations.
These criteria are only a few of the many factors necessary for complete disease eradication. There are also many economic, social, and political elements necessary for an attempted disease eradication to be successful. Collaboration is extraordinarily important—without the complete dedication of the governments, health providers, and people involved, eradication is simply not possible. Disease eradication is also highly resource-intensive, as research, vaccines, and other medications tend to be quite expensive. Commitment of resources, manpower, and political support on a global level is necessary to remove the effects of even a single disease from humankind.