The Challenge of Disease Eradication
Though we live in an age of conservation, the deliberate extinction of an ancient life form is being relentlessly pursued worldwide with increasing zeal. Encouraged by political leaders, financed by a coalition of industry, governments, private benefactors, and celebrities, but operating largely out of sight of the media, an army of professionals and volunteers has already eliminated this organism from over 175 countries. The world is standing by, not to mourn the senseless obliteration of yet another member of the earth's living heritage, but to celebrate the consignment to history of a disease that until recently was one of the world's most dreaded illnesses. Only 10 years ago, the poliovirus was paralyzing 1,000 children every day; today it is on the verge of being eradicated forever. Now, however, the greatest threat to delivering a polio-free world to future generations is complacency in the face of this disappearing disease.
Extinction by Another Name
Disease eradication has been described as the ultimate goal in public health. It entails not just the reduction of the target pathogen to zero, but also the eventual cessation of all control measures against it. While the humanitarian arguments for pursuing the eradication of an organism are compelling in themselves, the full benefits of these initiatives go far beyond the permanent elimination of a disease.
Eradication is also good economics. Though the ongoing global effort to eradicate polio will cost US$2.5 billion over 20 years, these costs pale against the US$1.5 billion that the world stands to save every year in direct costs alone once immunization efforts can stop.
Although at first glance eradication appears to be an elegant, cost-effective solution for tackling the diseases that plague mankind, few organisms are actually amenable to this solution. We lack the tools, resources, and commitment to launch and ensure the success of eradication initiatives against most pathogens. In general, an organism can only be eradicated if humans are essential to its life cycle, if there is no reservoir other than humans, and if it has no chronic carrier state. Thus, while HIV/AIDS, tuberculosis, and malaria together claim more than four million lives every year, not to mention the economic toll they exact, these diseases are not at present candidates for eradication.
Once a disease has met the biological criteria needed to be considered "eradicable," there must be an effective tool, whether a vaccine, drug, or other intervention, to efficiently interrupt transmission of the pathogen among humans. Even then the benefit of applying these tools in a massive eradication campaign must outweigh the financial, human, and other opportunity costs of such an effort. In addition, there must be social and political recognition of the value of seeking eradication, rather than just pursuing ongoing control of the disease. Perhaps most importantly, this commitment must be sustainable over the 10 to 20 years that will be required to implement the program. Such commitment is especially important and particularly difficult to secure during the final phase of an eradication initiative, when the target disease is rapidly disappearing and when the marginal costs of delivering the program are skyrocketing.
Even when the rigorous criteria outlined above are met, eradication remains a high-risk enterprise. Of the six initiatives that have been launched to eradicate a human pathogen in the last 100 years, three failed outright, two have yet to conclude, and only one has been unreservedly successful. Certification of the eradication of smallpox in 1980, with the rapid cessation of immunization against that disease, continues to stand as the only testament to humanity's capacity to successfully and permanently eliminate a disease that has plagued it throughout history.
The early eradication initiatives of this century targeting yellow fever, malaria, and yaws, a disease now confined to Africa, were fatally flawed from the outset due to an incomplete understanding of the biology of these diseases at the time. …