Matt Dixon and David L Heymann
Historically, infectious disease eradication campaigns have achieved differing levels of success, without reaching their ultimate goal. These past efforts have taught the science community a number of valuable lessons in what can be seen as an evolving process towards tackling a range of very different infectious disease targets.
Efforts to combar infectious disease are fought at various levels. The ultimate success is considered eradication, which means no infections in humans worldwide, none in a natural animal reservoir or host that could re-infect humans, and no more need for interventions unless there is an accidental or deliberate reintroduction of the infection. Smallpox is the only disease to have achieved this, and polio and guinea worm are currently targeted for eradication.
Another approach is to aim for elimination. This means stopping new infections in a defined geographic area, and then progressing to having the population in that region free of the disease. Continued interventions are required to prevent re-establishment in the area that has eliminated it. This strategy is being pursued against diseases such as elephantiasis, leprosy and river blindness.
For most other disease campaigns, control is the goal. Control programmes aim to reduce infections, illness and death to manageable levels, and this level varies depending on location. Consistent, sustained prevention measures and treatment are needed to keep the disease under control. As knowledge and technology advance, the goal for some diseases that meet the criteria for elimination or eradication can and does move from control to elimination, and with political will and adequate funding, from elimination to eradication.
The Case of Smallpox
In many ways, smallpox proved to be an 'ideal' candidate for disease eradication and, upon successful certification of eradication, provided science with a rigorous set of criteria for identifying future infectious disease eradication candidates. In 1967 the
Current Eradication Efforts: The Final Push
Two further eradication programmes have been established as a result of the lessons learned from past successes and failures, and these have been greatly aided by advances in epidemiology and operational research.
Dracunculiasis, commonly known as guinea worm disease, is caused by a parasitic worm. People become infected by drinking water contaminated with microscopic crustaceans infected with the larva of the worm. After the female worm matures in the human body, it creates a painful ulcer, usually on the leg, from which it ejects its larva when the infected person submerges the limb in water to relieve the burning. Encouraging the use of safe filtered drinking water through the provision of clean sources and simple homemade filters, health education activities, and the targeted destruction of the crustacean in the water, have constituted a comprehensive and highly successful package of interventions on which to base an eradication campaign. A 1991
The second infectious disease targeted for eradication is polio, selected by a
However, polio re-emergence does remain a threat outside of these countries; exportation of the virus from
Looking to the Future: New Eradication Targets
There have been calls for eradication of other key infectious diseases.
Scientists have also recently started to assess the feasibility of measles eradication. Measles elimination campaigns are ongoing in many parts of the world, and scope for eradication is being intensely scrutinised. Certain barriers will need to be addressed before eradication is attempted, which differ between developed and developing nations. In developed western countries where measles has been eliminated, there is a lack of urgency as the disease is no longer perceived as a serious public health threat and the presence of antivaccination movements makes it difficult to determine whether elimination can be sustained, and eradication attained. Within developing countries, measles transmission is widespread and intense, but in none more so than countries embroiled in conflict. This will raise similar issues currently faced by polio eradication efforts. It will require careful planning if a new campaign is to co-exist sustainably with the existing eradication efforts and other high-priority international health initiatives.
The challenges of achieving eradication are numerous and vary according to the disease in question. Surveillance, particularly in the latter stages of a campaign, combined with continued political and financial support, will be vital elements to any disease eradication programme. Polio and dranculiasis eradication efforts are nearing fruition, and the push from philanthropic foundations for other infectious diseases to be equally stamped out means there is cause for great optimism. However, this hope must be tempered with lessons of caution and vigilance, and eradication campaigns must ensure that realistic targets are set, given the current state of technologies and knowledge.
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