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  1. Article ; Online: Short Report

    Janet Ong / Joel Aik / Lee Ching Ng

    PLoS Neglected Tropical Diseases, Vol 15, Iss 6, p e

    Adult Aedes abundance and risk of dengue transmission.

    2021  Volume 0009475

    Abstract: Dengue is transmitted mainly by the adult female Aedes aegypti mosquito. However, little is known about the impact of adult Aedes abundance on the risk of dengue transmission. Here we analysed nationally representative dengue case and vector surveillance ...

    Abstract Dengue is transmitted mainly by the adult female Aedes aegypti mosquito. However, little is known about the impact of adult Aedes abundance on the risk of dengue transmission. Here we analysed nationally representative dengue case and vector surveillance data collected from Singapore, to determine the effect of adult Aedes abundance on the risk of dengue transmission. A case was an area with active dengue transmission as indicated by the presence of dengue cluster. A control was an area where no dengue cluster was reported. Using multivariate logistic regression, we analysed 88 cases and 602 controls and estimated the odds of dengue cluster formation at various adult Aedes abundance levels, estimated by the mean number of adult female Aedes per Gravitrap per week and categorised into Low, Moderate, High and Very High abundance level. We found that the risk of dengue cluster formation was positively associated with adult Ae. aegypti abundance. We observed a three to four-fold increase in the odds of dengue clusters forming in areas with High (AOR: 3.40, 95% CI: 2.09, 5.52) and Very High (AOR: 3.99, 95% CI: 2.46, 6.46) adult Aedes aegypti abundance level compared to those with low Ae. aegypti abundance level. Our study strengthens the evidence for the use of adult Aedes indices for dengue risk assessment and early warning for dengue outbreaks. Entomological indicators of adult Ae. aegypti could be used to anticipate and prioritize areas for dengue control.
    Keywords Arctic medicine. Tropical medicine ; RC955-962 ; Public aspects of medicine ; RA1-1270
    Language English
    Publishing date 2021-06-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Aedes aegypti exhibits a distinctive mode of late ovarian development

    Heng Zhang / Feng Guang Goh / Lee Ching Ng / Chun Hong Chen / Yu Cai

    BMC Biology, Vol 21, Iss 1, Pp 1-

    2023  Volume 18

    Abstract: Abstract Background Insects live in almost every habitat on earth. To adapt to their diverse environments, insects have developed a myriad of different strategies for reproduction reflected in diverse anatomical and behavioral features that the ... ...

    Abstract Abstract Background Insects live in almost every habitat on earth. To adapt to their diverse environments, insects have developed a myriad of different strategies for reproduction reflected in diverse anatomical and behavioral features that the reproductive systems of females exhibit. Yet, ovarian development remains largely uncharacterized in most species except Drosophila melanogaster (D. melanogaster), a high Diptera model. In this study, we investigated the detailed developmental process of the ovary in Aedes aegypti (Ae. aegypti), a major vector of various disease-causing pathogens that inhabits tropical and subtropical regions. Results Compared with Drosophila melanogaster, a model of higher Diptera, the processes of pole cell formation and gonad establishment during embryonic stage are highly conserved in Ae. aegypti. However, Ae. aegypti utilizes a distinct strategy to form functional ovaries during larval/pupal development. First, during larval stage, Ae. aegypti primordial germ cells (PGCs) undergo a cyst-like proliferation with synchronized divisions and incomplete cytokinesis, leading to the formation of one tightly packed “PGC mass” containing several interconnected cysts, different from D. melanogaster PGCs that divide individually. This cyst-like proliferation is regulated by the target of rapamycin (TOR) pathway upon nutritional status. Second, ecdysone-triggered ovariole formation during metamorphosis exhibits distinct events, including “PGC mass” breakdown, terminal filament cell degeneration, and pre-ovariole migration. These unique developmental features might explain the structural and behavioral differences between Aedes and Drosophila ovaries. Importantly, both cyst-like proliferation and distinct ovariole formation are also observed in Culex quinquefasciatus and Anopheles sinensis, suggesting a conserved mode of ovarian development among mosquito species. In comparison with Drosophila, the ovarian development in Aedes and other mosquitoes might represent a primitive mode in the lower ...
    Keywords Aedes aegypti ; Drosophila melanogaster ; Ovariole formation ; Terminal filament ; Cyst-like proliferation ; TOR signaling ; Biology (General) ; QH301-705.5
    Subject code 590
    Language English
    Publishing date 2023-01-01T00:00:00Z
    Publisher BMC
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: Public sentiments towards the use of Wolbachia-Aedes technology in Singapore

    Christina Liew / Li Ting Soh / Irene Chen / Lee Ching Ng

    BMC Public Health, Vol 21, Iss 1, Pp 1-

    2021  Volume 12

    Abstract: Abstract Background Wolbachia technology is a novel vector control approach that can reduce mosquito populations and the risk of mosquito-borne diseases, which has recently gained popularity amongst countries. In 2016, Singapore embarked on a multi- ... ...

    Abstract Abstract Background Wolbachia technology is a novel vector control approach that can reduce mosquito populations and the risk of mosquito-borne diseases, which has recently gained popularity amongst countries. In 2016, Singapore embarked on a multi-phased field study named Project Wolbachia – Singapore, to evaluate the use of Wolbachia technology as an Aedes aegypti mosquito population suppression tool to fight dengue. Due to the novelty of this technology in Singapore, this study aims to understand the public’s acceptance and sentiments towards the use of Wolbachia technology. Methods Several public sentiment survey approaches – including online, face-to-face in the streets, as well as door-to-door household surveys – were conducted. Results The surveys conducted prior to the first field releases and implementation of the project revealed high support for the use of Wolbachia technology in Singapore. A household perception survey conducted in the interim of the first project phase was encouraging, with the majority of the respondents being aware of the project and having no concerns with the release of male Wolbachia-carrying Aedes aegypti (Wolbachia-Aedes) mosquitoes in their neighbourhood. Conclusions The study reveal high support for the use of Wolbachia technology in Singapore and also provided invaluable insights that were used in the development of a public communications and engagement framework model, which thus helped to guide these elements in the subsequent phases and expansion of the project.
    Keywords Wolbachia ; Perception ; Survey ; Dengue ; Singapore ; Public aspects of medicine ; RA1-1270
    Subject code 380
    Language English
    Publishing date 2021-07-01T00:00:00Z
    Publisher BMC
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article ; Online: VKORC1 mutations in rodent populations of a tropical city-state as an indicator of anticoagulant rodenticide resistance

    Cliff Chua / Mahathir Humaidi / Erica Sena Neves / Diyar Mailepessov / Lee Ching Ng / Joel Aik

    Scientific Reports, Vol 12, Iss 1, Pp 1-

    2022  Volume 8

    Abstract: Abstract Anticoagulant rodenticides are commonly used in rodent control because they are economical and have great deployment versatility. However, rodents with Single Nucleotide Polymorphism (SNP) mutations within the Vkorc1 gene are resistant to the ... ...

    Abstract Abstract Anticoagulant rodenticides are commonly used in rodent control because they are economical and have great deployment versatility. However, rodents with Single Nucleotide Polymorphism (SNP) mutations within the Vkorc1 gene are resistant to the effects of anticoagulant rodenticide use and this influences the effectiveness of control strategies that rely on such rodenticides. This study examined the prevalence of rat SNP mutations in Singapore to inform the effectiveness of anticoagulant rodenticide use. A total of 130 rat tail samples, comprising 83 Rattus norvegicus (63.8%) and 47 Rattus rattus complex (36.2%) were conveniently sampled from November 2016 to December 2019 from urban settings and sequenced at exon 3 of Vkorc1. Sequencing analysis revealed 4 synonymous and 1 non-synonymous mutations in Rattus rattus complex samples. A novel synonymous mutation of L108L was identified and not previously reported in other studies. Non-synonymous SNPs were not detected in the notable codons of 120, 128 and 139 in R. norvegicus, where these regions are internationally recognised to be associated with resistance from prior studies. Our findings suggest that the prevalence of anticoagulant rodenticide resistance in Singapore is low. Continued monitoring of rodenticide resistance is important for informing rodent control strategies aimed at reducing rodent-borne disease transmission.
    Keywords Medicine ; R ; Science ; Q
    Language English
    Publishing date 2022-03-01T00:00:00Z
    Publisher Nature Portfolio
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article ; Online: Features of the urban environment associated with Aedes aegypti abundance in high-rise public apartments in Singapore

    Stephanie A Fernandez / Haoyang Sun / Borame L Dickens / Lee Ching Ng / Alex R Cook / Jue Tao Lim

    PLoS Neglected Tropical Diseases, Vol 17, Iss 2, p e

    An environmental case-control study.

    2023  Volume 0011075

    Abstract: Aedes aegypti abundance in residential estates is hypothesized to contribute to localised outbreaks of dengue in Singapore. Knowing the factors in the urban environment underlying high Ae. aegypti abundance could guide intervention efforts to reduce Ae. ... ...

    Abstract Aedes aegypti abundance in residential estates is hypothesized to contribute to localised outbreaks of dengue in Singapore. Knowing the factors in the urban environment underlying high Ae. aegypti abundance could guide intervention efforts to reduce Ae. aegypti breeding and the incidence of dengue. In this study, objective data on Ae. aegypti abundance in public apartment blocks estimated by Singapore's nationally representative Gravitrap surveillance system was obtained from the National Environmental Agency. Low and high abundance status public apartment blocks were classified based on the Gravitrap Aegypti Index, corresponding to the lowest and highest quartiles respectively. An environmental case-control study was conducted, wherein a blinded assessment of urban features hypothesised to form breeding habitats was conducted in 50 randomly sampled public apartment blocks with low and high abundance statuses each. Logistic regression was performed to identify features that correlated with abundance status. A multivariable logistic model was created to determine key urban features found in corridors and void decks which were predictive of the Ae. aegypti abundance status of the public apartment block. At a statistical level of significance of 0.20, the presence of gully traps [Odds Ratio (OR): 1.34, 95% Confidence Interval (CI): 1.10, 1.66], age of the public apartment block [OR: 2.23, 95% CI: 1.48, 3.60], housing price [OR: 0.33, 95% CI: 0.16, 0.61] and corridor cleanliness [OR: 0.67, 95% CI: 0.40, 1.07] were identified as important predictors of abundance status. To reduce Ae. aegypti abundance around public apartment blocks and potential onward dengue transmission, gully traps could be remodelled or replaced by other drainage types. Routine inspections of Ae. aegypti breeding should be targeted at older and low-income neighbourhoods. Campaigns for cleaner corridors should be promoted.
    Keywords Arctic medicine. Tropical medicine ; RC955-962 ; Public aspects of medicine ; RA1-1270
    Subject code 720
    Language English
    Publishing date 2023-02-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  6. Article ; Online: Singapore’s 5 decades of dengue prevention and control—Implications for global dengue control

    Soon Hoe Ho / Jue Tao Lim / Janet Ong / Hapuarachchige Chanditha Hapuarachchi / Shuzhen Sim / Lee Ching Ng

    PLoS Neglected Tropical Diseases, Vol 17, Iss

    2023  Volume 6

    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 ... ...

    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 ...
    Keywords Arctic medicine. Tropical medicine ; RC955-962 ; Public aspects of medicine ; RA1-1270
    Subject code 910 ; 390
    Language English
    Publishing date 2023-06-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  7. Article ; Online: Singapore's 5 decades of dengue prevention and control-Implications for global dengue control.

    Soon Hoe Ho / Jue Tao Lim / Janet Ong / Hapuarachchige Chanditha Hapuarachchi / Shuzhen Sim / Lee Ching Ng

    PLoS Neglected Tropical Diseases, Vol 17, Iss 6, p e

    2023  Volume 0011400

    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 ... ...

    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 ...
    Keywords Arctic medicine. Tropical medicine ; RC955-962 ; Public aspects of medicine ; RA1-1270
    Subject code 390
    Language English
    Publishing date 2023-06-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  8. Article ; Online: Non-Invasive Dengue Diagnostics—The Use of Saliva and Urine for Different Stages of the Illness

    Mahathir Humaidi / Wei Ping Tien / Grace Yap / Choon Rong Chua / Lee Ching Ng

    Diagnostics, Vol 11, Iss 1345, p

    2021  Volume 1345

    Abstract: Dengue diagnosis is largely dependent on clinical symptoms and routinely confirmed with laboratory detection of dengue virus in patient serum samples collected via phlebotomy. This presents a challenge to patients not amenable to venipuncture. Non- ... ...

    Abstract Dengue diagnosis is largely dependent on clinical symptoms and routinely confirmed with laboratory detection of dengue virus in patient serum samples collected via phlebotomy. This presents a challenge to patients not amenable to venipuncture. Non-invasive methods of dengue diagnosis have the potential to enhance the current dengue detection algorithm. In this study, samples from dengue infected patients were collected between January 2012 until September 2012 and September 2013 until December 2013 in two different setups. Panel A samples (blood, urine, and saliva) were collected daily when the 39 patients were hospitalised and during their follow-up visits while Panel B samples (saliva) were collected from 23 patients during the acute stage of dengue. Using DENV PCR on Panel A, from day 2 to day 4 post fever onset, serum showed the best overall positivity followed by saliva and urine (100%/82.1%/67.9%). From day 5 until day 10 post fever onset, serum and urine had similar positivity (67.4%/61.2%), followed by saliva (51.3%). Beyond day 10 post fever onset, DENV was undetectable in sera, but urine and saliva showed 56.8% and 28.6% positivity, respectively. DENV in urine was detectable up until 32 days post fever. Panel B results showed overall sensitivity of 32.4%/36% (RNA/NS1) for DENV detection in saliva. Our results suggest that the urine-based detection method is useful especially for late dengue detection, where DENV is undetected in sera but still detectable in urine. This provides a potential tool for the physician to pick up new cases in an area where there is ongoing dengue transmission and subsequently prompt for intensified vector control activities.
    Keywords dengue ; diagnostics ; non-invasive ; urine ; saliva ; Medicine (General) ; R5-920
    Subject code 630
    Language English
    Publishing date 2021-07-01T00:00:00Z
    Publisher MDPI AG
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  9. Article ; Online: A greener vision for vector control

    Shuzhen Sim / Lee Ching Ng / Steve W Lindsay / Anne L Wilson

    PLoS Neglected Tropical Diseases, Vol 14, Iss 8, p e

    The example of the Singapore dengue control programme.

    2020  Volume 0008428

    Abstract: Vector-borne diseases are a major cause of morbidity and mortality worldwide. Aedes-borne diseases, in particular, including dengue, chikungunya, yellow fever, and Zika, are increasing at an alarming rate due to urbanisation, population movement, weak ... ...

    Abstract Vector-borne diseases are a major cause of morbidity and mortality worldwide. Aedes-borne diseases, in particular, including dengue, chikungunya, yellow fever, and Zika, are increasing at an alarming rate due to urbanisation, population movement, weak vector control programmes, and climate change. The World Health Organization calls for strengthening of vector control programmes in line with the Global Vector Control Response (GVCR) strategy, and many vector control programmes are transitioning to this new approach. The Singapore dengue control programme, situated within the country's larger vision of a clean, green, and sustainable environment for the health and well-being of its citizens, provides an excellent example of the GVCR approach in action. Since establishing vector control operations in the 1960s, the Singapore dengue control programme succeeded in reducing the dengue force of infection 10-fold by the 1990s and has maintained it at low levels ever since. Key to this success is consideration of dengue as an environmental disease, with a strong focus on source reduction and other environmental management methods as the dominant vector control strategy. The programme collaborates closely with other government ministries, as well as town councils, communities, the private sector, and academic and research institutions. Community engagement programmes encourage source reduction, and house-to-house inspections accompanied by a strong legislative framework with monetary penalties help to support compliance. Strong vector and epidemiological surveillance means that routine control activities can be heightened to specifically target dengue clusters. Despite its success, the programme continues to innovate to tackle challenges such as climate change, low herd immunity, and manpower constraints. Initiatives include development of novel vector controls such as Wolbachia-infected males and spatiotemporal models for dengue risk assessment. Lessons learnt from the Singapore programme can be applied to other ...
    Keywords Arctic medicine. Tropical medicine ; RC955-962 ; Public aspects of medicine ; RA1-1270
    Subject code 360
    Language English
    Publishing date 2020-08-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  10. Article ; Online: Challenges in dengue surveillance and control

    Lee Ching Ng

    Western Pacific Surveillance and Response, Vol 2, Iss 2, Pp 1-

    2011  Volume 3

    Abstract: Globally, the challenge posed by dengue has escalated at an astonishing rate in the last three decades, with no sign of abating. It is estimated that dengue affects at least 50 million – 100 million people every year. With more than 120 dengue-endemic ... ...

    Abstract Globally, the challenge posed by dengue has escalated at an astonishing rate in the last three decades, with no sign of abating. It is estimated that dengue affects at least 50 million – 100 million people every year. With more than 120 dengue-endemic countries, 3.6 billion people are at risk of infection. More than 70% of those at risk reside in the Asia Pacific region, making this region an epicentre of dengue activity.In addition to making a comeback in places such as the Americas and Singapore, where dengue was previously successfully controlled for decades, the virus has also breached the subtropical-temperate barrier as it claims new territories. In the last decade, dengue transmission has extended its reach into places as far north as Nepal, Ningbo in China and France, and as far south as Bueno Aires in Argentina. The Pacific islands, with much lower population densities, have also not been spared, with increasing dengue outbreaks since the 1970s.The direct economic and social impact of dengue on dengue-endemic regions is high,9–12 and the burden in other aspects such as the security of blood supplies is increasingly being recognized. Dengue’s threat to travellers has also been systematically demonstrated by a 2008 study on 6957 travellers who returned ill and sought treatment from EuroTravNet centres. Of those travellers, 1.9% were diagnosed with dengue, and one of the three deaths reported was due to dengue shock syndrome.
    Keywords dengue ; surveillance ; control ; challenges ; Aedes ; western pacific region ; aegypti ; albopictus ; Medicine ; R ; Public aspects of medicine ; RA1-1270
    Language English
    Publishing date 2011-04-01T00:00:00Z
    Publisher World Health Organization Regional Office for the Western Pacific
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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