Tackling the dengue epidemic: learning from Singapore

Lionel WIJESIRI

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 Lanka.

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.

Vaccine

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.

Failure

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.

Approach

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;
*Enforcement; and
*Research

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 transmission.

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 effectively.

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.

ii) Schools

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 control operators.

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 regular basis.

(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.

Community involvement

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 various means.

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.