Eradication of Diseases

This article was first published in June 2014; last revised in October 2018.

The ultimate goal in the fight against infectious diseases is their eradication. This goal has already been achieved for two diseases: smallpox, a once deadly human disease, and rinderpest, a disease that affected animals.

In theory, many infectious diseases could be eradicated, in practice, however, only a handful of diseases can meet the criteria required for successful eradication.

The International Task Force for Disease Eradication (ITFDE) was formed in 1988 and it currently names seven eradicable diseases: polio, Guinea worm disease, Lymphatic filariasis, Cysticercosis, Measles, Mumps and Rubella.1 ITFDE also lists a number of diseases that, while at the moment are not eradicable, can be eliminated in certain parts of the world. These include diseases such as neonatal tetanus, yaws, malaria, rabies, trachoma and others.

In this entry we look at several aspects of disease eradication.

“Eradication” versus “Elimination”

The eradication of a disease is permanent and global, while the elimination of a disease is an achievement restricted to a specific geographic area.

  • Eradication of a disease refers to a deliberate effort that leads to the permanent reduction to zero of the worldwide incidence of infection caused by a specific agent.2

Eradication means that intervention measures are no longer required, the agent, which previously caused the disease is no longer present.

  • Elimination of a disease refers to the deliberate effort that leads to the reduction to zero of the incidence of infection caused by a specific agent in a defined geographic area. A disease can be eliminated from a specific region without being eradicated globally. Actions to prevent the disease from transmitting or re-emerging are still required once a disease is eliminated.3

What makes a disease eradicable?

It is not possible to clearly draw a line between eradicable and non-eradicable diseases. Diseases only became eradicable after scientific discoveries gave us the tools to fight them.

However two conditions are absolutely necessary for a disease to be eradicable and there are several characteristics of diseases which make it more likely for a disease to be eradicable.

Necessary conditions

It is an infectious disease

For a disease to be eradicable it needs to be a disease you can “catch”, for example from other humans or animals, i.e. it has to be infectious. Non-infectious diseases, such as heart disease or cancer, cannot be eradicated.

Measures against the disease exist

To eradicate a disease we need to know of measures to fight its spread. The summary table above illustrates the diversity of such means against diseases.

Whilst the characteristics of a disease are biologically-determined or fixed, the available measures against the disease can progress through our scientific understanding and technological developments. This is where human ingenuity makes the fight against a disease possible. We discuss the different types of measures against infectious diseases next.

Features which make eradication easier

There are five key characteristics which are not absolutely necessary but make eradication easier. Dowdle (1999) writes: “In theory if the right tools were available, all infectious diseases would be eradicable. In reality there are distinct biological features of the organisms and technical factors of dealing with them that make their potential eradicability more or less likely.”4

The disease is caused by only a small number of pathogens

Infectious diseases are caused by pathogens. These disease-causing microorganisms include bacteria, viruses, unicellular parasites, or larger parasites such as worms. We included them for all diseases discussed here in our summary table at the beginning of this entry. To eradicate a disease its pathogen needs to be eradicated. This means that diseases caused by one or a small number of pathogens are easier to eradicate than the ones caused by a larger number of pathogens. Examples make this clear:

  • Smallpox, for instance, is caused by only two types of viruses that were eradicated in 1977 using a vaccine.
  • Lung infections, on the other hand, are an example of a disease named after their shared symptom: infection of the lung. But these symptoms can be caused by a large number of viruses and bacteria. This makes the disease “lung infection” non-eradicable. Wound infections are an even more extreme example as they can be caused by many bacteria that would not be harmful to a healthy human with intact skin.

In other words, disease-causing organisms can be eradicated but not necessarily symptoms.

The disease has only a single host

Diseases that only infect one species are easier to eradicate than diseases that infect many species, i.e. that have “alternative hosts”. Smallpox, for instance, was caused by a virus that only survived in and spread among humans.

Other diseases that have only humans as a host are:

  • polio,
  • Guinea worm disease (dracunculiasis),
  • measles,
  • mumps,
  • pertussis (whooping cough), and
  • diphtheria.

Many diseases unfortunately either rely on several hosts (vector-transmitted) or can even have several hosts as alternative reservoirs:

Malaria, lymphatic filariasis, and river blindness are examples of vector transmitted diseases. This means that the pathogen requires several hosts in its life cycle. The malaria parasite, for instance, needs both humans and certain types of mosquitos to survive. In a hypothetical scenario of all humans being cleared of malaria at the same time, mosquitoes could still carry the disease and re-infect humans. However, if all humans could somehow be protected from infections for a few months at the same time, the malaria parasite would eventually die out as all malaria-carrying mosquitos naturally have a short life span. If the malaria parasite was therefore not able to live on in humans before the malaria-carrying mosquitoes die a natural death, the parasite would be eradicated.

The influenza virus (which causes influenza or “the flu”), is an example of a pathogen with several alternative hosts. The influenza virus can infect humans, birds, pigs and other animals. It could survive in these animals even if all humans were somehow made immune. This means that even if a vaccine against all strains of the influenza virus existed, one would still have to immunize all humans, pigs and even wild birds to eradicate influenza.

Other examples of diseases with alternative hosts are

  • rinderpest (infected cattle, buffalo, zebras, water buffaloes, African buffaloes, elephants, kudu, wildebeest, various antelopes, bushpigs, warthogs, giraffes, sheep, and goats);
  • hepatitis A (which infects humans and other vertebrates);
  • ebola (infects bats as well as some bigger mammals);
  • rabies (infects all warm-blooded vertebrae including all mammals); and
  • Japanese encephalitis (a so-called dead-end disease in humans, sheep, and cattle, which means that it is fatal and cannot spread, and is only transmitted among pigs).

While it makes eradication easier when there is only one host, we know it is not a requirement: Rinderpest was successfully eradicated in 2011 and it was a disease with alternative hosts that affected cattle, sheep and goats but also antelopes, buffaloes, deers, giraffs, wildebeests and warthogs. However, most cases occurred in domesticated animals so that eradication was achieved by vaccinating all domestic species in parallel.

Diseases that are vector transmitted will be easier to eradicate than those with alternative hosts, because one has to eradicate the pathogen from only one species for a sufficiently long time.

The fact that the pathogen is reliant on several hosts makes vector transmitted diseases easier to eradicate than diseases with several alternative hosts but harder to eradicate than diseases with just one host. In reality, more factors play a role in determining whether a disease is eradicable or not. Malaria, for instance, is a vector-transmitted disease but it is not currently eradicable because no good measures exist against it.

The disease is visible and good diagnostics exist

Good monitoring of outbreaks is essential for eradicating a disease as it allows us to contain an outbreak and prevent the spread of the disease.

If the disease has visible symptoms in the majority of infections or when a good diagnostic method exists, monitoring is easier. A smallpox infection, for instance, always led to visible pox and made monitoring simple. Pictures of infected people were shown and allowed health workers to find cases even in remote villages.5

Less visible diseases are harder to monitor. If symptoms only show in a minority of infections (e.g. polio) or if a diagnosis is difficult the disease can more easily spread unnoticed.

Another aspect that makes monitoring harder is if a disease is stigmatized. Sexually transmitted diseases for example might be hidden from the community intentionally.

Elimination has proven possible

It is promising if a disease has already been eliminated from certain geographical areas such as islands or even whole world regions.6

If, on the other hand, no country has ever eliminated a disease, it is likely that the current means against a disease are not effective enough yet to make eradication possible.7

Once a geographic region or indeed most countries worldwide have eliminated a disease, eradication becomes a feasible target. Currently there are three diseases that fall in this category: Polio, Guinea worm disease, and yaws.

The perceived disease burden is high and financial, political and community support are available

The perceived burden of a disease, the estimated cost of eradication, and the political stability of affected countries are further factors that determine the eradicability of diseases.

Polio is a good example here as it illustrates the powerful impact of both a unified international effort and local political support. In 1988, the Global Polio Eradication Initiative was set-up which has provided large-scale and, importantly, continued support for the eradication of polio. The number of paralytic polio cases has been greatly reduced such that in 2018 it is considered endemic in only three countries: Pakistan, Afghanistan, and Nigeria.

But polio also illustrates that positive developments might reverse. Nigeria’s case numbers, for instance, surged from 202 in 2002 to 1143 in 2006 because of suspicions that immunization campaigns were a cover for Muslim sterilization by the US government which lead to an 11-month 8boycott. The example of polio hence illustrates the importance of both international as well as local community support for eradication.

However, only Chad and Ethiopia recorded a positive number of Guinea worm cases in 2017.

The line chart illustrates the dramatic decline in the number of reported Guinea worm cases from two different data sources. From more than 892,000 reported cases in 1989, the number of reported Guinea worm infections dropped to only 25 infections worldwide in 2017 – 13 in Chad and 12 in Ethiopia.

For the early period especially the number of reported cases is much lower than the true number of cases. Greenaway (2004) reports an estimate of 3.5 million cases for the year 1986.9

The means to fight the spread of diseases

Essential for the eradication of diseases is the development of means to fight their spread – the second essential factor in the list above. Over the last centuries we have developed several means to fight the spread of infection and some of these have the potential to eradicate a specific disease entirely.

The appropriate measure to fight the disease depends on the type of pathogen and the way of transmission. For instance, antibiotics only work against bacteria, whilst anti-retrovirals only work against retroviruses. The way the disease is transmitted matters as well: if diseases spread via drinking water, filtering can stop the disease; if spread via mosquitoes, bed nets can stop the disease, etc.

Different means stop different pathogens

The type of pathogen causing the disease is the first characteristic of a disease that informs the choice of appropriate measures against the disease.

These measures can be grouped into three categories, which are summarised in the figure.

The appropriate measure depends on the specific disease. Both smallpox and rinderpest were eradicated using vaccines. However, vaccines have not been developed against every disease yet, so other methods like water decontamination, wound treatment and health education to block transmission can be used with great success as well, such as in the case of Guinea Worm (dracunculiasis).

Different transmission routes of the disease require different strategies

The list below – based on Checchi (2009)11– describes the routes of transmission various infectious diseases.

Direct transmission routes (suitable for ring-vaccination)

  • Air droplets: Inhalation or eye contact with infected droplets generated by breathing, sneezing, coughing. Less than 1 m distance required.
    • smallpox, rinderpest, rubella, PPR (ovine rinderpest), whooping cough (pertussis), common cold, flu (influenza), meningitis
  • Sexual: Transmission by unprotected sex.
    • HIVsyphilis, chlamydia, gonorrhoea, hepatitis B
  • Blood: Directly transferred from one person’s blood to another person’s blood, e.g. via unsafe injections or transfusions of unsafe blood.
    • HIVhepatitis B and C
  • Mother to child (vertical): Transmission during pregnancy, childbirth or via breast milk.
    • HIVtetanus, syphilis, hepatitis B
  • Any body fluid: Body fluids (blood, feces, vomit, breast milk, urine, semen) entering broken skin or mucosa (nose, mouth, vagina, anus)
    • ebola
  • Skin-to-skin contact:
    • yaws

Non-direct transmission routes 

  • Airborn: Infection possible by entering a room an infected person was previously in or through air conditioning.
    • tuberculosis, smallpox (rarely), measles, chickenpox
  • Fecal-oral: Ingestion of faecal matter, facilitated by poor water, sanitation and hygiene conditions. Can be transmitted through objects.
    • poliomost intestinal worms including pork tape worm, typhoid, hepatitis A and E, diarrhoeal diseases including cholera, shigella, salmonella, E. coli, rotavirus, amoebiasis, giardiasis
  • Vector-borne: Pathogens undergo a life cycle inside humans as well as inside another “vector” species, typically insects.
    • malaria (mosquito)Carrion’s disease (phlebotomine sand flies), lymphatic filariasis (mosquito), river blindness (Black fly), dengue fever (mosquito), Japanese encephalitis (mosquito), African sleeping sickness (Tsetse fly), leishmaniasis (Sand fly), schistosomiasis (fresh-water snail), typhus (lice, fleas, mites), relapsing fever (lice, ticks)
  • Wounds: Deep cuts, infection of the umbilical cord after birth, animal bites
    • rabies, tetanus
  • Water, soil: 
    • Guinea worm (ingesting water), tetanus (infection through wounds, from soil), hookworm (walking barefoot on soil, or ingestion)

For those diseases that spread through direct contact between people – those listed under direct-transmission routes – the ring-vaccination principle can be applied. It allows to only vaccinate all people who came or will come in contact with an infected person, rather than vaccinating the whole population, to save money and time. This principle was successfully applied for the eradication of smallpox.12

Measures against the spread of disease10
Measures against disease spread

Benefits of eradicating diseases

The immediate benefit of eradicating a disease is obvious: preventing the suffering and saving the lives of people who would have been infected with this disease in the future.

But there are additional benefits from eradicating a disease:

  1. Removing a disease from the list of existing diseases makes doctor’s lives easier and patient’s lives better by reducing the chance of mis-diagnoses.
  2. No medication is needed to treat an eradicated disease. This slows the emergence of resistance. Take for example the (hypothetical) eradication of a bacterial disease. No more antibiotics will be used to treat cases (and suspected cases) of this disease. The reduced usage of antibiotics will slow the spread of resistance to antibiotics.13
  • A disease that is eradicated can also no longer mutate or re-combine with other pathogens to form novel diseases.
  • The final benefit is saving cost in the long term. In several ways eradicating a disease reduces expenditure in the future:14
    • The direct effect is that the eradication reduces the costs of prevention and treatment.
    • The indirect effect is that it decreases spending on diagnosing the disease and research into the disease.
    • Lastly, there is also the effect of having a more healthy population that as a consequence is more productive.

    Therefore eradication has economic benefits in the long term as more money is saved than the eradication campaign costs. This possibility is illustrated in the schematic comparison.

    Eradicating vs controlling a disease: schematic comparison of the costs
    Costs of controlling vs eradicating a disease 1

    How much should we spend on eradicating diseases?

    The eradication of a disease has several benefits as we have just seen. But whether it is worth spending money on a disease eradication program at a given time needs to be assessed for each disease separately.

    There will always be other good causes we can spend money on. These include non-health causes, other health causes, the eradication of different diseases, and even research into more cost effective tools for eradication of a disease instead of eradicating it with existing means. The scenario or intervention which brings the highest benefit needs to be assessed for each disease separately. Elimination and eradication are the ultimate goals of public health. The only question is whether these goals are to be achieved in the present or [by] some future generation.15

    Successfully eradicated diseases

    The table summarizes some of the key facts about diseases on the eradication agenda [Clicking on the table will open it in higher-resolution]. Even though these are all infectious diseases, the variety of pathogens and available treatments vary greatly. Also, the case-fatality rates — the likelihood with which an infection will lead to death — range from zero to one hundred percent.

    The interactive chart displays the annual number of cases of the some of the diseases discussed in this entry: it includes data for the already eradicated disease smallpox and those diseases for which eradication is underway.16

    The chart shows the global number of cases, but by clicking on “Change country” on the bottom left of the chart it is possible to see the number of cases in any country of the world.

    Smallpox: 200 years between vaccine and the disease eradication

    The last recorded case of smallpox occurred in 1977 in Somalia. The disease was officially declared eradicated by the World Health Organization in 1980.

    Below we provide key charts illustrating the elimination of smallpox disease; you can find out more about the disease and its history in our much more comprehensive Smallpox entry.

    From the invention of vaccine against smallpox by Edward Jenner in 1796, it took almost two centuries to eradicate the disease.

    It was only with the establishment of the World Health Organization in the aftermath of World War II that international quality standards for the production of smallpox vaccines were introduced and the fight against smallpox moved from national to an international agenda. In 1966, the WHO launched the Intensified Smallpox Eradication Program. By then smallpox cases and deaths in Europe and North America had been driven down substantially but large parts of Asia and Africa still struggled under smallpox’s disease burden.

    Shown in the chart are the number of reported smallpox cases from 1920 until the last case in 1977. Even though smallpox had high visibility and should therefore have been relatively easy to document, the lack of an international organization dedicated to global health means the number of cases was likely much greater.

    The world map illustrates the year the variola virus (the virus that caused smallpox) was no longer endemic in a country.17 You can see that Somalia was the last country to eliminate smallpox in 1977.

    Rinderpest: eradication began before vaccine against the disease was available

    Rinderpest is the only animal disease that has been eradicated so far. Rinderpest outbreaks in cattles used to cause devastating losses for animal farmers. The eradication efforts began in the 1920s before the vaccine against the rinderpest virus was even available. Measures such as animal quarantine and slaughter were used to contain the disease.

    The map here shows the last year in which cases of rinderpest were reported in a country. In 1960 an English veterinary scientist Walter Plowright has developed a vaccine against rinderpest, which finally led to its eradication.

    You can read more about the history of rinderpest eradication in our post here.

    Diseases on track or being eradicated

    Polio

    Here we only show the chart illustrating the elimination of polio globally. We provide detailed information on polio and its history in our comprehensive Polio entry.

    Polio, short for poliomyelitis, is a disease that is caused by the poliovirus.

    Ho Jonas Salk and Albert Sabin invented two polio vaccines in 1953 and 1961, respectively, which eliminated polio from the United States and Canada in 1979 and rapidly lead to a large reduction of the disease in the Western Europe. While Salk’s vaccine required injection with a needle, Sabin’s vaccine is oral and can be swallowed. The latter feature made its distribution throughout the developing world possible, as fewer trained healthcare staff were required for its administration.

    The chart here highlights the global decline of the estimated number of paralytic polio cases from 1980 onwards. In the peak year 1981, the number of paralytic polio cases are estimated to have exceeded 450,000 but were reduced to 43 cases in 2016 – a more than 100,000-fold reduction of paralytic polio cases. As of 2019, wild polio virus is endemic in only three countries: Afghanistan, Nigeria, and Pakistan. In 2018, 9 countries have reported samples (human or environmental) positive for vaccine-derived poliovirus.

    Guinea worm (dracunculiasis)

    Guinea worm disease is caused by Dracunculus medinensis worm. There is no vaccine against the disease, however, it can be successfully eliminated by identification and treatment all current cases of the disease.

    In 2018, 28 cases of Guinea worm have been reported, these where in Angola (1 case), Chad (17 cases) and South Sudan (10 cases).18

    You can read more about the disease and its eradication here.

    Diseases that could be eliminated in some parts of the world

    The process of disease eradication is always ongoing. As new treatments become available ans as we start to better understand the disease ecology new avenues open for disease eradication.

    There is no one defined path for disease eradication. Eradication is usually the final goal, and control of disease spread or local disease elimination is usually a more near-future goal for most diseases.

    On the list of diseases that could potentially be eliminated in parts of the world are yawns, rabies, malaria, measles, neonatal tetanus, trachoma, rubella and mumps.

    Useful references

    Hopkins (2013)
    • Description: A good summary of the methods available to eradicate Ginea worm disease, polio, malaria, lymphatic filariasis and river blindness. Figure 1 of the paper is especially helpful as an illustrated summary.
    • Date of publication: 3 January 2013
    • Available at: http://www.nejm.org/doi/full/10.1056/NEJMra1200391

    Online publication The History of Vaccines
    • Description:This web publication is brought out by The College of Physicians of Philadelphia and describes disease eradication in general (see link below) but also on specific vaccine-preventable diseases (found in the table of content on the left) in an accessible and interactive way.
    • Date of publication: Last updated 25 January 2018
    • Available at: https://www.historyofvaccines.org/content/articles/disease-eradication

    Hemingway (2017)
    • Description:This article discusses how vector-borne diseases, specifically with insects like malaria, can be controlled, eliminated or even eradicated.
    • Date of publication: 24 November 2017
    • Available at: http://science.sciencemag.org/content/358/6366/998

    Vaccinating wild animals

    Data sources

    We provide all data sources for this entry on a separate page.