Is Disease Eradication Always the Best Path?

Sara Gorman from Harvard University discusses the pitfalls of disease eradication efforts.

McFadden G (2010) Killing a Killer: What Next for Smallpox? PLoS Pathog 6(1): e1000727. doi:10.1371/journal.ppat.1000727

There is no question that the eradication of smallpox, a devastating illness costing millions of lives, was one of the greatest achievements of 20th-century medicine. The disease was triumphantly declared eradicated by the World Health Assembly in 1980. Smallpox eradication required extremely focused surveillance as well as the use of a strategy called “ring vaccination,” in which anyone who could have been exposed to a smallpox patient was vaccinated immediately. Why was smallpox eradication possible? For one thing, smallpox is easily and quickly recognized because of the hallmark rash associated with the illness. Second, smallpox can be transmitted only by humans. The lack of an animal reservoir makes controlling the illness much simpler.

The success of smallpox eradication campaigns has resulted in persistent calls to eradicate other infectious diseases in the years since 1980. Unfortunately, disease eradication can be difficult and even impossible in the case of many infectious diseases, and it is crucial to consider the features of each illness in order to come to a proper conclusion about whether the pursuit of disease eradication is the best approach. In the first place, it is important to be clear about what “eradication” means. Eradication refers to deliberate efforts to reduce worldwide incidence of an infectious disease to zero. It is not the same as extinction, the complete destruction of all disease pathogens or vectors that transmit the disease. Elimination, a third concept, encapsulates the complete lack of a disease in a certain population at a certain point in time. Disease eradication therefore specifies a particular strategy for dealing with infectious diseases; other options exist that in some circumstances may be more desirable.

Can the pursuit of disease eradication ever be detrimental? It could be in the case of certain diseases that do not lend themselves easily to total eradication. A claim of eradication logically ends prophylactic efforts, reduces efforts to train health workers to recognize and treat the eradicated disease, and halts research on the disease and its causes. When eradication campaigns show some measure of success, financial support for the control of that illness plummets dramatically. Wide dissemination of information about eradication efforts without the certification of success can therefore prove detrimental. In these cases, complacency may prematurely replace much needed vigilance. If there is a reasonable chance of recurrence of the disease or if lifelong immunity against the disease is impossible, then attempting eradication may prove disastrous because infrastructure to control the disease would be lacking in the event of resurgence. Tracking down the remaining cases of an illness on the brink of eradication can be incredibly costly and divert government money in resource-poor nations from more pressing needs.

Another potential problem with disease eradication efforts is that, as a vertical approach, they may drain resources from horizontal approaches, such as capacity building and health system strengthening. Some advocate a more “diagonal” approach that uses disease-specific interventions to drive improvements of the overall health system. Still others have argued that vertical approaches that treat one disease at a time may divert resources from primary healthcare and foster imbalances in local healthcare services. Vertical schemes may also produce disproportional dependence on international NGO’s that can result in the weakening of local healthcare systems.

Malaria offers an excellent example of a case in which debate rages about whether eradication efforts would be successful. There are four species of single-cell parasite that cause malaria, the most common of which are P. falciparum and P. vivax. P. falciparum is the most deadly and P. vivax is the most prevalent. These two species make it difficult to engineer a single, fool-proof vaccine. Further complicating developing a vaccine for malaria are the ability of the parasites to mutate so that even contracting malaria does not confer life-long immunity. Furthermore, malaria involves an animal vector (mosquitoes). It would clearly be a huge challenge and perhaps even impossible to wipe out malaria completely. Beginning in 1955, there was a global attempt to eradicate malaria after it was realized that spraying houses with DDT was a cheap and effective way of killing mosquitoes. The initiative was successful in eliminating malaria in nations with temperate climates and seasonal malaria transmission. Yet some nations, such as India and Sri Lanka, had sharp reductions in malaria cases only to see sharp increases when efforts inevitably ceased. The state of affairs in India and Sri Lanka demonstrates some of the negative effects of eradication campaigns that are not carried to fruition. The project was abandoned in the face of widespread drug resistance, resistance to available insecticides, and unsustainable funding from donor countries. This failure was detrimental because the abandoned vector control efforts led to the emergence of severe, resistant strains that were much harder to treat.

Recently, discussions of malaria eradication have begun again. At the moment, there is considerable political will and funding for malaria eradication efforts from agencies such as the Gates Foundation. The Malaria Eradication Research Agenda Initiative, in part funded by the Gates Foundation, has resulted in substantial progress in identifying what needs to be done to achieve eradication. Even so, proponents of malaria eradication admit that this goal would take at least 40 years to achieve. It is not clear how long current political will and funding will last. There are concerns that political will might wither in the face of the estimated $5 billion annual cost to sustain eradication efforts.

Disease eradication can clearly be an incredibly important public health triumph, as seen in the case of smallpox. But when should the strategy be employed and when is it best to avoid risks associated with eradication efforts that might fail? Numerous scientific, social, and economic factors surrounding the disease in question must be taken into consideration. Can the microbe associated with the disease persist and multiply in nonhuman species? Does natural disease or immunization confer lifelong immunity or could reinfection potentially occur? Is surveillance of the disease relatively straightforward or do long incubation periods and latent infection make it difficult to detect every last case of the illness? Are interventions associated with eradication of the disease, including quarantine, acceptable to communities globally? Does the net benefit of eradication outweigh the costs of eradication efforts? Proposals for disease eradication must be carefully weighed against potential risk. Rather than being presented as visionary, idealistic goals, disease eradication programs must be clearly situated in the context of the biological and economic aspects of the specific disease and the challenges it presents.

 The author declares no competing interests.

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11 Responses to Is Disease Eradication Always the Best Path?

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  3. Roland Chee says:

    Your article haas good arguments. I add that: Plasmodium knowlesii is a fifth species of malaria that infects humans, and is a zoonosis whereby the vector are monkeys.

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  4. Prashanth says:

    Disease eradication/elimination must be something that districts/regions identify and make (if necessary) vertical prorammes for AT THEIR LEVELS. The present trend assumes a globa proportions and priorities are set far away from the places where these “burdens” exist, reducing people to robots by over-standardised global guidelines, neglecting local priorities and cultures. This is even disruptive, let alone being a poor strategy.

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    • Sara Gorman says:

      Thanks for your comment. I don’t think there’s anything inherently wrong with global disease eradication programs. I just think they need careful monitoring and thought to be successful and that it is always a good idea to allow for open dialogue about their potential shortcomings.

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  6. George D says:

    Yet some nations, such as India and Sri Lanka, had sharp reductions in malaria cases only to see sharp increases when efforts inevitably ceased. The state of affairs in India and Sri Lanka demonstrates some of the negative effects of eradication campaigns that are not carried to fruition. The project was abandoned in the face of widespread drug resistance, resistance to available insecticides, and unsustainable funding from donor countries.

    That much is true. After insecticide and drug resistance rose, and local elimination efforts were abandoned and control efforts scaled back, Sri Lanka saw a huge increase in malaria cases and deaths. From a low of just 17 cases in 1963, the country went back to having 250,000 cases per year by the late 1980s.

    Having learned from the failures of the past, the country again engaged in an elimination project, and is once again on the edge of elimination. It is expected to be declared malaria free (no local transmission in three years) in 2014. (See http://www.ucsf.edu/news/2012/08/12645/malaria-nearly-eliminated-sri-lanka-despite-decades-conflict for a striking illustration of the decline). The country is on the edge of elimination. China had 30 million cases per year in the 1950s, and now has less than 30,000. It too is looking at prospective elimination (as are many other formerly highly endemic countries, such as Panama and Brazil). Challenging geography, poverty, the risks of resistance, and vector behaviour are all things to be overcome. With investments in research, technology, and implementation, these things are overcome. Even India, thought to be the last refuge of polio, has been certified disease free, and has seen very large reductions in malaria – without the level of effort needed to reach elimination.

    In almost every case, the costs incurred by local elimination and then control are similar or less than the costs incurred by allowing the disease to remain endemic. Pooled collectively, the costs of disease eradication are almost always tens or hundreds of times lower than the costs of allowing the disease to sustain indefinitely. (Assuming future people are not discounted to zero, as is often the case in econometric analyses). Where countries are incapable of achieving such things on their own, concentrated aid combined with country determination, as we currently see in Pakistan and Afghanistan’s polio elimination efforts, is sufficient to take us the last mile.

    I’m afraid that in using the example of Sri Lanka, without reference to current circumstances, you’ve drawn entirely the wrong conclusions. There are diseases that are ineradicable with current technologies, knowledge, and resources. Plasmodium knowlesi is one. That’s okay. We’ll get through falciparum and vivax first, and take on the other malarias later.

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    • Sara Gorman says:

      Thanks for your comment. I agree there have been considerable strides in malaria elimination in many countries. My point was not to attack malaria elimination/eradication programs by any means but simply to use malaria as an example of the ways in which eradication efforts must be carefully weighed against the challenges posed by the particular disease in question. Smallpox was a very particular case, given the readily-identifiable symptoms and the lack of an animal reservoir. But will eradication work so well in every case? Possibly not. That’s why it’s essential to think twice before assuming that eradication is always the best plan. The current situation with polio is perhaps a good example. Efforts to eradicate polio consume about $1 billion annually. The long-term pay-off of eradication would be enormous, but some experts are still wondering whether perpetual control of the disease would make more sense, logistically and financially. Of course, eliminating the last few cases of a disease will always be the most expensive task. One of the points you highlight, with which I of course agree, is that elimination/eradication projects in poor countries usually require high levels of sustained funding from the United States and other Western governments. But the buzz word in Washington these days is “sustainability,” i.e. whether a program can eventually run on its own without U.S. financial assistance. With the federal budget under extreme pressure, there is a concern that countries that are pursuing elimination/eradication programs will find them untenable if American aid decreases, as it very well may, in the near future.

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  7. Rajan Nepali says:

    A nice article backed with facts! Actually, elimination and eradication of a few diseases seems feasible, provided favorable circumstances. One of the examples as far as I can grasp is polio. But there are many pitfalls behind the inability to eradicate it completely from the world. Possible pitfalls can be negative social and religious stigma towards polio vaccination and corrupt health system. By social and religious constraints, I mean, unnecessary and at times forceful alignment of polio vaccine with certain religious entities such as in the case of Pakistan. The other side of the coin is corrupt health system-inability of leadership to control negative stigma among the people by influential religious leaders and impotency towards effective implementation of vaccination program (coverage) and its thorough monitoring and evaluation (Quality assurance).

    Meanwhile, a part from India and Srilanka, Nepal is one more country which not only failed to eradicate malaria but also had to change the program’s very name [from "National Malaria Eradication Programme (NMEP)" launched in 1958 to "Malaria Control Program" in 1978].

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    • Sara Gorman says:

      Many thanks for your comment. I absolutely agree that social, cultural, and religious components of vaccine resistance are a large part of the equation. This is one of the biggest challenges facing polio eradication now.

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