Dr. Cockburn defines the eradication of disease as the extinction of the pathogen from the human population. This is reasonable since this is what the word implies, but he deems it important to emphasize this since others have applied the term to control programs with aims falling short of this. The essential operational difference between eradication and control programs is that the latter requires continued effort, but the former is terminated if successful.

Eradication is difficult and costly and has not been accomplished for any infection. The host range of the disease agents is an important factor in determining the likelihood of success of eradication, for agents limited to domestic animals might be controlled by test and slaughter programs, while those with wild animal reservoirs pose more difficult problems. The eradication of disease agents whose host is man may depend on the degree of evolutionary divergence between the human parasites and related species infecting other animals; the greater the divergence, the lower is the likelihood that the human agents will reappear from the animal species.