Singapore’s 5 decades of dengue prevention and control—Implications for global dengue control

Abstract

This paper summarises the lessons learnt in dengue epidemiology, risk factors, and prevention in Singapore over the last half a century, during which Singapore evolved from a city of 1.9 million people to a highly urban globalised city-state with a population of 5.6 million. Set in a tropical climate, urbanisation among green foliage has created ideal conditions for the proliferation of Aedes aegypti and Aedes albopictus, the mosquito vectors that transmit dengue. A vector control programme, largely for malaria, was initiated as early as 1921, but it was only in 1966 that the Vector Control Unit (VCU) was established to additionally tackle dengue haemorrhagic fever (DHF) that was first documented in the 1960s. Centred on source reduction and public education, and based on research into the bionomics and ecology of the vectors, the programme successfully reduced the Aedes House Index (HI) from 48% in 1966 to <5% in the 1970s. Further enhancement of the programme, including through legislation, suppressed the Aedes HI to around 1% from the 1990s. The current programme is characterised by 4 key features: (i) proactive inter-epidemic surveillance and control that is stepped up during outbreaks; (ii) risk-based prevention and intervention strategies based on advanced data analytics; (iii) coordinated inter-sectoral cooperation between the public, private, and people sectors; and (iv) evidence-based adoption of new tools and strategies. Dengue seroprevalence and force of infection (FOI) among residents have substantially and continuously declined over the 5 decades. This is consistent with the observation that dengue incidence has been delayed to adulthood, with severity highest among the elderly. Paradoxically, the number of reported dengue cases and outbreaks has increased since the 1990s with record-breaking epidemics. We propose that Singapore’s increased vulnerability to outbreaks is due to low levels of immunity in the population, constant introduction of new viral variants, expanding urban centres, and increasing human density. The growing magnitude of reported outbreaks could also be attributed to improved diagnostics and surveillance, which at least partially explains the discord between rising trend in cases and the continuous reduction in dengue seroprevalence. Changing global and local landscapes, including climate change, increasing urbanisation and global physical connectivity are expected to make dengue control even more challenging. The adoption of new vector surveillance and control tools, such as the Gravitrap and Wolbachia technology, is important to impede the growing threat of dengue and other Aedes-borne diseases.

Associations between Dengue Incidence, Ecological Factors, and Anthropogenic Factors in Singapore

“…Furthermore, the tropical climate is ideal for year-round breeding of the Aedes aegypti vector, facilitating endemic dengue transmission. However, due to a comprehensive vector control program, the force of infection has steadily decreased, concomitantly with dengue seroprevalence across all age groups [ 18 , 19 ]. This has led to a low level of herd immunity, particularly among the young [ 18 ], enabling explosive outbreaks to occur once dengue transmission takes hold.…”

Efficacy ofWolbachia-mediated sterility for control of dengue: emulation of a cluster randomized target trial

“…While four long-term Wolbachia field trial townships were not randomly pre-selected, we emulated constrained randomisation protocols for cluster-randomised trials by randomly selecting a set of 12 control townships, such that the historical dengue incidence of the intervention arm is similar to that of the control arm in the pre-intervention period 4,11 .This further prevents chance-imbalance in baseline dengue risk due to the small number of intervention (n=4) locations considered (See Supplementary Information). All locations practiced the same baseline dengue control protocol in the pre- and post-intervention periods 2,3 .…”

“…In Singapore, 133,821 individuals reported for febrile illness and were tested for dengue at the Environmental Health Institute, hospital laboratories and commercial diagnostic laboratories, through general practitioner clinic, polyclinic or public/private hospital from EW1 2019 – EW 26 2022. All dengue-suspect patients were tested using either using an internally controlled RT-qPCR assay, dengue non-structural protein 1 (NS1) or IgM as diagnostic assays to detect dengue virus in serum samples 3,11 . We excluded individuals who were tested on more than one occasion in 4 weeks, individuals who had more than one residential address in different control or intervention townships and individuals who had been tested at different labs with conflicting dengue results.…”

“…Vector control remains the primary tool for mitigating the spread of dengue due to the lack of available therapeutics and highly effective vaccines globally. Conventional vector control measures include environmental management, source reduction and insecticide use 2,3 . While these measures can reduce the burden of dengue, they are resource intensive and yield diminishing returns.…”

Precision Prediction for Dengue Fever in Singapore: A Machine Learning Approach Incorporating Meteorological Data

“…In the tropical city-state of Singapore, despite ongoing rigorous vector control measures and public health interventions, DF continues to be a persistent issue. The existing measures to combat dengue, including vector control, public education, and vaccination (CYD-TDV, Dengvaxia), have shown limitations [ 7 ], highlighting the need for innovative and effective strategies. Therefore, there is a pressing need to develop more precise and robust prediction models for DF.…”