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Omaima Ali
Eradication of infectious disease: Holy Grail or poisoned chalice?
The human race has been battling infectious diseases for the past 7000-8000 years; however it was only
as late as the mid-20th century that the concept of infectious disease eradication became a possibility
with the discovery of antibiotics, the development of vaccines and epidemiology.1 Eradication has been
at the forefront of public health ever since, ‘evolving naturally from disease control’.2 The prospect of
living in a world free from the suffering and economic and health pressures of infectious diseases is no
doubt enticing but it begs the question: ‘can the pursuit of disease eradication ever be detrimental?’3
The costs and benefits of eradication
Smallpox was the first and only human disease to be eradicated; the last case was identified in 1977
when a hospital cook from Somalia4 became infected with a weaker strain of the virus.5 This was 10
years after renewed efforts to eradicate the disease and an increase in funding of US$ 2.4 million
initiated the launch of the Intensified Smallpox Eradication Programme.6 The campaign was largely
successful due to the distinctive features of the disease. It was ‘highly visible’7; victims would develop a
severe rash allowing effective diagnosis and monitoring of the infection.8 Moreover, there was no
known animal reservoir for the disease (so once it was wiped out in humans, smallpox would be
completely eradicated)7 and the vaccine that was eventually developed was effective in over 95% of
those immunised.9 Not only was the eradication of smallpox considered one of the greatest medical
breakthroughs in history, it also saved the lives of the millions of people who could have suffered the
same fate of the 2 million that died from smallpox every year before the campaign launched.16
Proposals to eradicate other infectious diseases such as polio and measles became inevitable after
smallpox was eliminated. Polio was considered to meet certain criteria for eradication and so in 1985,
the Pan American Health Organisation (PAHO), with the assistance of the World Health Organisation
(WHO) commenced a global eradication programme.1 Like smallpox, the polio virus has no known nonhuman reservoir.10 However, hopes to mirror the achievements of the smallpox programme were quickly
diminished as the campaign faced many obstacles. Immediate diagnosis and disease control were
difficult as there are no obvious symptoms of the infection7 and the strain on resources and provision of
the programme, coupled with the need to coordinate 20 million volunteers in over 200 countries11 has
cost $9 billion since the campaign began in contrast to the $500 million that was needed to eradicate
smallpox.12
Is this crusade against polio really worth the economic losses in eradicating rather than
controlling the disease? Global incidence of polio cases have declined by over 99% since the launch of
the programme and increasingly efficient surveillance systems have managed to control its spread.13 In
the long term, polio eradication could result in either the cessation of immunisations or the replacement
of the oral polio vaccine (OPV) with the inactivate polio vaccine (IPV), saving at least $40 billion by
2035 as opposed to controlling the disease.14, 17 However, this is a big and expensive ‘if’, as the
continued use of the OPV in countries like Ukraine and Pakistan, has highlighted the risk of the
poliovirus mutating and so developing resistance, which may stretch hopes of complete eradication even
further away.37
Eradication efforts have the benefit of improving sanitation, societal wellbeing and the socio-economic
conditions that exist in a particular region. This is exemplified by the steps taken to wipe out Guinea
worm disease (GWD) by The Carter Center since 1986.10 The global prevention and eradication
programme involves improving water supply by constructing wells and boreholes and applying
larvacide to contaminated water.20 This combined with health education communicated through radio
campaigns and posters, reduced the incidence of GWD by 81% in Nigeria over an astonishing period of
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3 years. 20 In the long-term, these strategies enable families in developing countries to improve their
living standards (e.g. improved hygiene awareness) and reduce the burden of other diseases such as
cholera and Chagas’ disease. Infectious diseases such as pneumonia and malaria along with the effects
of undernutrition, have a marked impact on the likelihood and the age at which young children enrol at
school.36 The poor quality of education they receive as a result of tackling these health complications
during childhood, serves as a barrier to social mobility and, on a grander scale, the economic
development of poorer countries.36
The transmission of infectious diseases is exacerbated by the threat of wars, violence, lack of political
leadership and growing global inequality, all of which impede the ability of eradication programmes to
implement coordinated strategies.1 International political commitment was strong during the smallpox
eradication campaign. The period of détente in the Cold War over the 1970s helped to create stability in
international relations.1, 21 Despite this, the Ethiopian civil war and the uncooperative behaviour of
Somali government officials (until the appointment of a new national eradication programme manager
in February 1977) rendered the last few cases of smallpox the most difficult to wipe out.15, 22
Recent polio outbreaks in Syria demonstrate the fragility of the relationship between
infectious diseases and violence.23 An effective eradication programme since 1964 rid the country of an
outbreak for two decades until polio’s return to Aleppo in October 2013. The lack of clean water and
hospitals and a sewage-ridden environment along with an immunity gap (due to access of vaccines
being denied to rebel-held regions) created ideal conditions for the polio virus to thrive. Since then, a
network of volunteers and health teams have been travelling across the warzone, carrying OPV in
coolers to administer to children who had not been immunised since the war broke out. 24
An eradication campaign could potentially turn out to be a poisoned chalice for primary healthcare
services. A shift in epidemiological patterns from infectious diseases to mainly non-communicable
diseases has led to chronic conditions such as heart disease and stroke being the world’s leading causes
of death. 18, 19 There is growing concern that to eradicate an infectious disease, resources will be diverted
away from those health issues that are gaining prominence.2 It is therefore important that national
spending on healthcare is adequate enough to support the advancement of general medicine and
infrastructure. This is so that primary healthcare services do not deteriorate once an eradication
programme is introduced and the quality of these services is fundamental in determining the success of
an eradication campaign.
“Eradication and on-going programmes constitute potentially complementary approaches to
public health. There are areas of potential overlap, conflict and synergy that must be recognized
and addressed. In many cases the problem is not that eradication activities function too well but
that primary health care activities do not function well enough.”2 (Walter R. Dowdle)
The presence of political will and international consensus are crucial in maintaining sustained interest8,
worldwide appeal and support for a campaign, as well as in overcoming the complacency presented by
nations and investors once an eradication programme starts to show signs of success 3.2 Eradication
efforts are vital in promoting synergy in public health; in a world where the threat of infectious diseases
were reduced, it would provide the platform to discuss the management and prevention of other health
issues.
Post-eradication challenges
The major challenge of post-eradication strategies is reaching a consensus over when to cease
immunisations and how widespread they should be.8 There is disagreement over the fate of vaccinations
that range from their complete cessation to continuous immunisation, 25 which mainly stem from
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differing views on how extensive vaccine coverage should be to impede transmission in a population.8
Mathematical models can be used to calculate the scale of mass vaccination required to achieve herd
immunity by studying the relationship between the number of secondary cases caused by a single
primary infection (its reproduction number (Ro)) and the average age of immunisation and infection.8
For instance, measles has a much larger Ro value than influenza and Ebola and a lower average age of
infection (five years). Therefore, theoretically at least 95% of a given population should be vaccinated
to achieve herd immunity.26
The calculation does not take into account the fact that there won’t be equal coverage of vaccines in a
population, as city and rural population totals and attitudes towards vaccination vary.26 This leads many
to advocate 100% immunisation to protect the whole population against an infectious disease.26
However, it has been proposed that this sort of mass vaccination creates an apparently sterile
environment where disease outbreaks are still possible. This was illustrated when a measles outbreak
occurred at a school in the USA in 1983.
“The affected high school had 276 students and was in the same building as a junior high school
with 135 students. A review of health records in the high school showed that all 411 students
had documentation of measles vaccination on or after the first birthday, in accordance with
Illinois law.”27
This has led to the suggestion that it would be better for a larger proportion of the population to develop
natural immunity to a pathogen27, something that would be impossible for future generations in the posteradication era of an infectious disease.
Concerns about the capacity of healthcare services to respond to the re-emergence of an infectious
disease highlight the need for continued monitoring, research and vaccine development.8 After
successful eradication, the education and training of healthcare workers to respond to and recognise the
eradicated disease will inevitably deteriorate.3 Furthermore, the reduced maintenance and improvement
of diagnostic tools and surveillance of a particular disease will make the re-emergence of an infectious
disease more difficult to cope with than it was during its eradication campaign.8 It would therefore seem
that we would be more suited to dealing with an outbreak in a world where the infectious disease was
not completely eradicated but controlled.
One thing to also consider is that an infectious disease could intentionally be reintroduced by those
seeking to do harm. Following the eradication of smallpox, stocks of the virus were sent to either one of
two WHO laboratories in Russia and the USA, however, labs were also given the option of destroying
their stocks.1, 8 Whilst 57 of the 75 labs that stockpiled the virus claimed to have transferred their stocks,
the World Health Organisation did not confirm these reports.8 An article in the New York Times in 1999
quoted a US government intelligence analysis, concluding that North Korea, Iraq and Russia were
keeping secret stocks of smallpox to use as a bio-weapon.28 Nevertheless, the risk of a bioterrorist attack
is extremely low 28 as it would be more practical for terrorists to use another weapon of mass destruction
than to waste their efforts on weaponising the complex smallpox virus29. Despite this, many countries
began to stockpile smallpox vaccines1 including the UK, which spent £32 million on 20 million
vaccines in 2002 in response to the 9/11 attacks in the USA.28
Natural Selection, the Immune System and the environment
Throughout human history, our contest with infectious diseases has helped to shape our genetic
variation30 as natural selection allowed the strongest (those with advantageous alleles against a disease)
to survive.31 Malaria has played an influential role in human evolution. It is more likely to affect the
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young (who have weaker immune systems), leaving behind children with malaria-resistant genes. In this
case, natural selection occurs before those children affected have any offspring and those who are
protected against malaria are therefore more likely to pass on their beneficial genes to the next
generation.31
However, this survival of the fittest is not as important today as natural immunity to certain
infectious diseases isn’t essential. Humans have created vaccines to prevent and treat infectious diseases
like malaria31 and biological factors as well as cultural, dietary and behavioural adaptations influence
our immunity against a disease32. In this case, the benefits of eradicating an infectious disease outweigh
the unforeseen impacts that the loss of these diseases would have on our immune systems and human
evolution. It still ensures that the strongest survive, albeit in a less competitive environment.31
Furthermore, it is important to appreciate that in modern societies there are characteristics significantly
more crucial than ‘strength’. We need only look at Stephen Hawking to see an example of someone who
has transcended their ‘selective weakness’ to the benefit of humanity.
Natural selection has resulted in the resistance of many bacterial pathogens to the antibiotics that were
once used to treat them, such as Staphylococcus aureus (evolving into the infamous MRSA) and
Mycobacterium tuberculosis.33 As well as using antibiotics to treat human infections, 60% of the
antibiotics produced in the UK are used in farming and agriculture to prevent, rather than cure bacterial
infections in cattle.34 The overuse and misuse of antibiotics promotes the rise of resistant pathogens that
are harder to treat and destroy. Antibiotic resistance is now one of the most serious international public
health threats of our time. Where antibiotics were once the holy grail of medicine that saved billions of
lives since their mass production in the 1940s, they are now unable to control many multidrug-resistant
pathogens.33 A review commissioned by David Cameron in 2014 predicted that, by 2050, drug-resistant
infections could kill more than 10 million people globally each year.38 On one hand, the successful
eradication of a bacterial pathogen would ensure that the pathogen could no longer develop resistance.
However, an eradication campaign may provide a selective pressure for bacteria to become resistant and
this would result in more harm than good; the proportion of antibiotic resistant strains would escalate
and the majority of the available stockpile of antibiotics would be ineffective against them.
Over 20 new diseases have emerged since the 1970s. The majority of these originated as a result of
human behaviour (increased mobility and travel) and changes in the local environment (clearing forests
for agriculture and migration).35 High population densities also boost the transmission of infectious
diseases. In ‘An Essay on the Principle of Population’, Thomas Malthus highlights the pressures
presented by a rapidly growing population on the environment and its resources. He argues that, disease
and famine are naturally-occurring population checks that are vital in maintaining population levels so
they do not exceed their local carrying capacity. However, food and resource production have actually
increased at a faster rate than the population due to technological advances and the Green Revolution,
which may suggest that these population checks are unnecessary. Despite this, overpopulation still poses
a serious threat to climate change and food production.39 Whilst Malthus’ approach may seem harsh, it
is not difficult to comprehend why some people may agree that infectious diseases are a natural and
important population check. They help to prevent populations from spiralling out of control, especially
in developing countries where family planning and contraceptive prevalence rates are low.
Conclusion
It is clear that different infectious agents have different unique characteristics that make them more or
less susceptible to eradication. A targeted approach should therefore be applied with a specific focus on
the amount of resources (political, financial and material to name but a few) that would be required and
the potential economic, health and social consequences of a proposed eradication campaign. Therefore,
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whilst a complete eradication of all infectious disease is a poisoned chalice, targeted eradications of
specific infectious agents following the example of smallpox is a holy grail worth chasing.
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