Eradication and elimination: facing the challenges, tempering expectations
The words eradication, elimination and control have been regularly defined in attempts to avoid inappropriate use of terminology
while addressing the realities and challenges of public health programmes.1,2
Whitty3
has recently outlined the dangers of raising expectations in the face
of political, financial, biological and logistical
efforts of eradication or elimination programmes,
emphasising these risks in search of a holy grail. Bockarie et al.4
noted five categories that defined the elimination or endgame
challenges—biological, socio-geographic, logistic, strategic
and technical—providing examples from current
programmes. These have created significant strategic and resource
impediments
to progress in implementation, requiring changes in
approach often with significant financial implications.
A variety of strategies are used to reduce
incidence and prevalence of infectious diseases: vaccination (smallpox,
polio,
measles), chemotherapy (onchocerciasis, lymphatic
filariasis, schistosomiasis), vector control, (onchocerciasis, malaria,
schistosomiasis) and provision of improved clean
water and sanitation (trachoma, guinea worm, soil transmitted helminths,
schistosomiasis). Such strategies are more
effective when combined, for example, chemotherapy, vector control and
behaviour
change, thereby achieving proportionately greater
and more rapid impact on transmission.
Eradication as a concept is specifically
defined as a reduction to zero global incidence of a specific pathogen,
not a disease,
which results from such an infection. This
represents a crucial distinction—the words disease and infection are
often used
interchangeably but incorrectly. Even WHO reporting
recently on the yaws programme in India entitled their publication
‘Eradication
of yaws in India.’ Thus, even WHO are unable to
consistently use correct terminology. Another example is the call for
the
eradication of malaria. However, eradication is
defined as the removal from the planet of a specific infection; raising
the
question, which of the five human species of Plasmodium is to be targeted? This is yet to be specified.
If an organism, such as the smallpox
virus, is maintained in the laboratory then the infection is considered
eradicated but
it is not extinct. In the case of smallpox, the
virus was maintained in the USA and the Soviet Union (Russia). A global
certification
process is required for those organisms targeted
for eradication and a Declaration of Global Eradication is required from
WHO.
For Dracunculiasis (guinea worm disease),
an independent body, the International Commission for the Certification
of Dracunculiasis
Eradication, was established to oversee the process
to conform with WHO's legal obligations through World Health Assembly
resolutions. Members are appointed by the Director
General of WHO to assess the validity of the evidence that transmission
of Dracunculus medinensis has been achieved in previously endemic countries. Countries with no evidence of infection are required to submit a statement
that transmission does not take place.5
Countries that have been certified following scrutiny of the evidence
presented require a visit to validate the information
provided to WHO by an independent certification
team. If certified, countries are required to maintain vigilance that
they
remain transmission free through continued
surveillance and maintenance of a rumour register. Any rumour should be
investigated
within 24 hours of being reported and the national
reward system to do this should be continued. The responsibility for
‘proving
a negative’ is a significant one if the target is
global eradication or country or regional elimination. Evidence must be
robust with regular assessments and surveillance
for at least 3 years after the interventions have stopped.
The smallpox programme in its final stages
introduced a global reward of US$1000 to report any suspected case.
Such a system
will need to be established for guinea worm when
all countries have been certified free of transmission. To date, some
194
countries and territories have been certified free
of transmission. There remain four Guinea worm endemic countries: Chad,
Ethiopia, Mali and South Sudan. The challenges of
the endgame and the costs of driving transmission to zero country
incidence
are exemplified3,4
in high unit costs per case detected, in remote settings where health
systems are weak, where surveillance and communication
a challenge, and where civil unrest and conflict
prevail. The recent experience of the polio eradication programme in
Pakistan
testifies to the security challenges.
UN access to endemic areas may not be
permitted for security reasons potentially preventing certification to
validate the
situation on the ground. Proving a negative to the
satisfaction of an independent body will be a challenge despite the
remarkable
gains made in the guinea worm programme to date,
with the two most endemic countries, Ghana and Nigeria, recently
certified
as free of transmission.6 The question of the use of the term ‘eradication’ following the findings of dogs infected with D. medinensis in Chad,7
and the possibility that the infection can be transmitted without the
human host involvement, poses significant problems
in confirming global eradication. In addition,
post-intervention surveillance periods are necessary prior to any final
assessment
by an independent body to verify absence of
transmission. The assessments required to provide sufficient evidence
that transmission
has been arrested are potentially expensive when
needed at scale and in all previously endemic countries.
Elimination is defined in a geographical
context where transmission has been verified as having been arrested in a
defined
geographic location. Previously, eradication has
been inappropriately used to define this situation. Most recent examples
of achievements in verification of the absence of
transmission are Onchocerca volvulus in Colombia and Ecuador,8
while Mexico and Guatemala are documenting similar achievements through
dossiers submitted to the Pan American Health Organization
(PAHO). The remaining endemic countries in this
region, Brazil and Ecuador, if regional elimination is to be declared,
have
to ensure that the remote Yanomami communities on
the border areas are accessible for regular ivermectin treatment,
preferably
more than once a year, or are treated with the
macrofilaricide, doxycyline. The Yanomami endemic area illustrates the
challenge
of reaching remote communities where access is
limited, where communities are migratory and health services sparse or
non-existent.
The African Programme for Onchocerciasis
Control (APOC) changed its objective from control to elimination after
it was demonstrated
that transmission could be reduced if sustained
high coverage of annual ivermectin treatment could be achieved over a
period
of 15–17 years in Senegal and Mali9 and in Kaduna State, Nigeria.10 However, the aspiration to eliminate transmission of O. volvulus
throughout all endemic areas of Africa requires extension of programmes
into areas not previously treated. The change from
a highly successful control programme to one of
elimination emphasises the increased costs of going the last mile in a
greatly
expanded programme. Will the costs of expansion of
long-term treatment and of verifying that transmission has been arrested
in some of the more remote and inaccessible parts
of Africa over the long-term be sustainable? Proving to the satisfaction
of an independent body that there is zero
transmission over all the endemic areas of Africa has long-term
financial, coordination
and human resource implications.
Lymphatic filariasis has been verified as
eliminated in China and South Korea some 15 years ago. In China this
followed several
decades of interventions of chemotherapy and vector
control. The current programme for the elimination of lymphatic
filariasis
as a public health problem has also achieved
significant gains, providing evidence that transmission has been
arrested in
several countries thereby ensuring that no clinical
cases will emerge following the cessation of mass drug administration.
Again the challenge of obtaining the requisite
evidence at scale globally will be a financial and logistic challenge
based
on the need to verify in 70+ endemic countries that
transmission, the key parameter of success, has been arrested even if
the public health problem has been alleviated.
The use of the term ‘as a public health problem’ has been addressed3
in the case of the leprosy elimination programme. Success in the use of
multi-drug therapy to reduce the public health problem
in many countries has resulted in the perception
that there remains a limited problem despite the large number of cases
that
remain in highly populous countries such as India.
The definition of a public health problem is a subjective view and the
parameters for such a definition dependent on
expert opinion. While the desire to eliminate local transmission in
perpetuity
can be achieved in certain isolated geographic
settings, the balance between true elimination and elimination of a
public
health problem will continue to be debated. The
availability of interventions and, often, donated drugs to impact on the
health
of the poor should not be a reason for avoiding
responsibility to provide resources to implement activities that will
have
a significant public health impact despite the fact
the ultimate goal of total transmission control is difficult to
achieve.
The term eradication has been used to
describe success in several isolated, often island, settings. More
correctly, elimination
should be the term applied. Examples of attempts at
elimination of cystic hydatid disease to reduce human incidence of Echinococcus granulosus
from Iceland in the 1800s, Cyprus, Tasmania, the Falkland Islands and
New Zealand provide an insight into the application
of a range of measures to prevent transmission.
Dogs were prevented from access to sheep offal and purged to remove
tapeworms,
destruction of cyst-infected sheep carcasses
instituted and extensive health education campaigns.11 All these island programmes were carried out over a period of decades, with New Zealand and Tasmania declaring provisionally
they were free of hydatid disease in 2002. The elimination of the transmission of O. volvulus on the island of Bioko, following vector control of the Bioko form of Simulium yahense, has also been achieved.12 However, given that in Bioko S. yahense was a unique cytoform, it can be claimed that not only was elimination of transmission achieved but also extinction of a
unique vector form.
The debate around issues of eradication
and elimination will continue. However, although the challenges are
well-defined,
the spectrum of these challenges, given they will
play out over the long duration of programmes, will need continuous
responses
by the many stakeholders who have invested in them.
The complexities of eradication and elimination and the public health
policy issues generated require a deep
understanding of the many dimensions that confront decision makers. As
programmes evolve
and complexities increase,13
the dynamic of changing biological, ecological and political scenarios
over long periods of time demand an inbuilt flexibility
and capacity to respond. The necessary response to
these inevitable challenges requires vision, finance and commitment by
the stakeholders of these programmes. Removing the
last filarial worm or gametocyte in remote and insecure settings, and
verifying
to the scientific community that the evidence is
sufficiently robust to declare eradication or elimination has been
achieved,
seems optimistic given the constraints identified
and the biological capacity of our targets to challenge us. The
objectives
of eradication or elimination are laudable but
prove costly. We should recognise that solving a public health problem
is indeed
a significant benefit, which has been achieved in
many settings, and that the search for the holy grail may take longer
than
expected.
source : http://inthealth.oxfordjournals.org/content/7/5/299.full
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