Tackling the dengue epidemic: learning from Singapore
Official statistics revealed recently that 74 people have died and
nearly 15,000 have been affected by dengue in the past six months. It
was said that numbers were increasing rapidly. It seems that dengue
fever and dengue haemorrhagic fever are re-emerging in full force in Sri
The Health Minister blamed it on the lackadaisical attitude of the
authorities concerned to take precautionary measures. He added, "The
country has 45 ministries, but only nine have appointed Dengue Control
Committees. Only four out of 90 departments have responded to the
circular by the Secretary to the President directing all government
institutions to set up Dengue Control Committees".
The minister has a valid point. Health Ministry on its own will never
be able to deliver the expected results unless the total support of all
sections is obtained.
Dengue is transmitted by several species of mosquito within the genus
Aedes, principally A. aegypti. The virus has four different types;
infection with one type usually gives lifelong immunity to that type,
but only short-term immunity to the others. Subsequent infection with a
different type increases the risk of severe complications. As there is
no vaccine, prevention is sought by reducing the habitat and the number
of mosquitoes and limiting exposure to bites.
While vaccines for other flaviviruses such as yellow fever and
Japanese encephalitis have been developed, dengue vaccine development is
complicated by the need to incorporate all four virus serotypes into a
single preparation. Experts believe that an approved vaccine is not
likely to be available for five to seven years; the only way to prevent
dengue transmission, therefore, is by vector control.
If we go back to history, dengue has been successfully prevented
through vector control in three instances. The first of these was the
highly successful, vertically structured paramilitary hemispheric
eradication campaign directed by the Pan American Sanitary Board (later
Pan-American Health Organization) 1946 to 1970. The second was also a
rigorous, top-down, military-like vector control operation in Cuba that
was based on intensive insecticidal treatment followed by reduction of
available larval habitats in 1981. Neither of these programmes, however,
was sustainable. The third successful programme was in Singapore.
The remorseless progression of the 20-21st centuries dengue pandemic
tells us that large-scale control of Aedes aegypti has been among their
most conspicuous public health failures.
Why is this? Professor Scott B. Halstead has the answer. He is
currently Adjunct Professor at the Department of Preventive Medicine and
Biometrics, Uniformed Services University of the Health Sciences,
Bethesda, USA, and Research Director and Senior Advisor, Pediatric
Dengue Vaccine Initiative.
“There are many reasons for the failure,” he says, “Among them,
limited national and global resources, failure of planners to recognize
that dengue imposes an important financial and social burden, the
regional nature of the dengue problem, absence of proven and sustainable
vector control methods, the confusion caused by the squabble between the
proponents of 'eradication' and 'control' strategies, indecisiveness
because of waiting for a dengue vaccine, and the generally doleful
support for and leadership by the public health sector. In short, dengue
is a paradigm for unsolved 21st century health problems.”
One might say that there is no point in dwelling on the reasons for
the failure to control Aedes aegypti, although a great deal can always
be learned by examining the past. Instead, we should direct our full
attention to the question of what can be done to improve the chances of
success of controlling dengue in the new century.
It follows that successful control of dengue will require a major,
sustained, cooperative and well-funded effort. We cannot hope to
approach dengue control except by re-prioritizing society’s social
goals, creating new partnerships and developing new tools through an
imaginative programme of enhanced research.
It is in this context that we could learn from the Singaporean
experience. WHO agrees Singapore is on the right path.
National Environment Agency (NEA) is vested with the responsibility
of adopting counter-measures to the dengue menace in Singapore. Its key
strategy in dengue control is to tackle the root of the problem, which
is to deny Aedes mosquitoes the place to breed (i.e. source reduction).
NEA adopts a multi-pronged approach to control dengue. The main
thrusts in our approach are:
*Preventive surveillance and control;
*Public education and community involvement;
Preventive surveillance and control
Through data gathered during field surveillance and with the aid of
the Geographical Information System, NEA conducts daily mosquito
surveillance operations. The information enables NEA to move quickly
into areas to do source reduction (i.e. remove/destroy breeding grounds
found). These are important steps to prevent possible dengue
NEA's operations strategies are: (a) active surveillance in areas
prone to dengue and/or where there is high mosquito population, (b)
breaking the source of transmission as quickly as possible when cases
(both suspected and confirmed) and clusters of cases emerge.
NEA has a considerable manpower deployment for mosquito control and
consists of dedicated teams responsible for regular auditing,
inspections and enforcement in each of the 84 constituencies. These
teams, being familiar with the areas under their charge, are able to
identify and pre-empt potential problematic areas quicker and more
NEA works with various land agencies as well as private organizations
and associations to ensure that there is a coordinated approach in
keeping the mosquito population and dengue cases low.
Some of the agencies NEA has worked with include:
i) Construction sites
An Environmental Control Officer (ECO) Scheme had been introduced in
construction sites. Under the scheme, construction sites are required to
engage a part time or full time ECO depending on the cost of the
development. These NEA-trained ECOs are responsible for maintaining the
mosquito control works within the construction sites.
A programme was introduced to train Operation Managers of schools on
dengue prevention. Through the training, these Managers have a deeper
knowledge of mosquito control and are able to audit the performance of
their mosquito control operators more effectively.
iii) Local Councils
NEA had assisted local bodies to kick-start a dedicated mosquito
control programme. The dedicated programme focuses the dengue control
efforts on source reduction. Apart from providing technical
specifications for dengue control works, NEA also provided some
financial assistance for these programmes. Local Council officers were
also trained as Estate Environmental Officers so as to equip them with
the necessary mosquito control knowledge and skills to supervise the
performance of pest control operators.
iv) Inter-Agency Dengue Task Force
The Chief Executive of NEA chairs the Inter-Agency Dengue Task Force
(IADTF) comprising of 25 government agencies and private associations.
Through IADTF, NEA leads other government agencies to similarly enhance
their mosquito control programmes. This collaboration has enhanced the
communication and coordination on dengue control efforts among various
agencies. Each agency has put in place a tighter and more comprehensive
source reduction regime in their mosquito control contracts with pest
Furthermore, permanent solutions to eliminate potential sources of
stagnant water like repairs to infrastructure, sealing up of cracks,
backfilling of land, and removal of roof-gutters are carried out on a
(c) Intensive Source Reduction Exercises (ISREs)
As NEA officers carry out routine surveillance checks every day,
additional pre-emptive Intensive Source Reduction Exercises (ISREs) are
carried out ahead of the warmer months to pre-empt the rise in dengue
fever cases. ISREs consist of coordinated search and destroy operations
carried out to remove mosquito breeding habitats (including potential
habitats), hence suppressing the rise in mosquito population during
warmer months. The operations cover all public areas and residential
estates, as well as premises belonging to government agencies.
Active community involvement is the key to keep the mosquito breeding
low in homes. To engage the community, NEA adopts a two-pronged
communication approach that incorporates a national publicity strategy
and a series of target-group specific (e.g. residents, foreign workers/
domestic workers and outbound travellers) outreach programmes.
Reaching Out Through 3P (People, Private and Public Sectors) Partners
To effectively reach out to different segments of the population, NEA
works very closely with 3P (People-Public-Private Sectors) partners to
jointly develop and roll out dengue prevention activities through
Recognising the disease burden and a different epidemiological
profile, Singapore started a research programme three and half years
ago. Code named STOP Dengue, it had four objectives: (1) Scientific
exploration of disease pathogenesis,(2) Translational research for
improved clinical management, (3) Operational evaluation for
introduction of intelligent, vector control measures and (4) Preventive
measures through innovative treatment strategies for Dengue.
The ultimate aim is to translate research into clinical management
that results in zero dengue fatality in Singapore.