SINGAPORE: More than 4,000 dengue cases have been reported since the start of 2020 – about twice the number of cases seen within the same period a year ago.
A key concern is the growing evidence of a sustained switch in the predominant dengue virus serotype, the National Environment Agency (NEA) said in a news release on Sunday (Mar 22).
Dengue virus serotype 2 (DENV-2) is the more predominant strain, but there has been an increase in dengue virus serotype 3 (DENV-3) cases lately.
"NEA has seen an increase in DENV-3 cases over the past four months," the agency said.
“The monthly proportion of DENV-3 cases in February was approximately 48 per cent, almost double the proportion of DENV-2 cases at 26 per cent."
It said the rise in proportion of DENV-3 cases is of concern, "as we have not had dengue outbreaks driven by DENV-3 in Singapore for almost three decades".
"This means that our population has lower immunity to DENV-3, and consequently a large proportion of our population is susceptible to DENV-3 infection," NEA said.
NEA is monitoring the situation to see if DENV-3 will emerge as the predominant strain and replace DENV-2.
“The combination of a potential sustained change in the predominant dengue virus serotype, coupled with the high Aedes aegypti mosquito population in some areas, and the unusually high number of dengue cases seen currently, could create a momentum of transmission that may drive even more dengue cases when we enter the warmer months ahead,” NEA explained.
“The warmer months from June to October usually see higher transmission of dengue in Singapore, due to accelerated development of the Aedes mosquito and shorter incubation period of the dengue virus.”
There could be an increasing trend of dengue cases in the second half of 2020 if additional proactive steps are not taken to manage the mosquito population, the agency added.
EFFORTS TO CURB DENGUE
Minister for the Environment and Water Resources Mr Masagos Zulkifli called for a “concerted and collective effort to step up prevention of mosquito breeding”.
As part of efforts to combat the issue, NEA brought forward the launch of the annual National Dengue Prevention Campaign to March, taking into account the dengue outlook for the year.
The focus of the campaign this year, it said, was to raise residents’ awareness that clean, stagnant water – as small as a 20-cent coin – can be a critical breeding ground for mosquitoes.
NEA highlighted the need for “community-led outreach” to protect neighbourhoods from dengue.
“Over the past three years, more than 3,000 mosquito breeding habitats were linked to containers and receptacles found at public areas," NEA said.
“About 65 per cent of these receptacles – such as plastic containers and empty drink cans – had been discarded as litter by people.
“We have also observed a 90 per cent increase in the detection rate of Aedes mosquito larval habitats found in homes, over the past three years.”
PENALTIES HANDED OUT TO OFFENDERS
There have also been stepped up checks by NEA and other parties leading up to the traditional peak dengue season, to remove potential mosquito breeding habitats in public areas and housing estates.
“Of the 498 clusters notified this year, about 80 per cent have been closed, with the concerted efforts of our partners and the community," the agency said.
“The 183-case cluster at Begonia Drive, 154-case cluster at Elias Road, 148-case cluster at Jalan Bangau, and 106-case cluster at Gangsa Road, were closed in the first three months of the year."
But there are still large clusters in Jurong West Street 91, Ang Mo Kio Avenue 3, Pavilion Circle and Berwick Drive, it cautioned.
Last year, NEA conducted about 900,000 inspections islandwide for mosquito breeding, including about 6,400 checks at construction sites. It uncovered more than 16,000 mosquito breeding habitats.
About 8,700 enforcement actions have been taken against owners of premises for mosquito breeding, with about 490 summonses and 26 Stop Work Orders issued to construction sites. Fifteen contractors were charged in court for repeat offences.
USING TECHNOLOGY IN FIGHT AGAINST DENGUE
In January this year, NEA completed the deployment of Gravitraps - which is used to monitor the Aedes mosquito population - to private landed estates, complementing those already at HDB estates since 2017.
“We now have more than 64,000 Gravitraps deployed islandwide, to monitor the Aedes mosquito population in Singapore,” it said.
"The data on mosquitoes caught in these traps have guided NEA’s inspection focus, thus enabling more targeted deployment of limited manpower resources," the agency added.
"The traps have also played a role in helping NEA remove adult Aedes aegypti mosquitoes, including female mosquitoes infected with dengue.
"Deployment of Gravitraps complements the efforts of the community, owners of premises and other stakeholders, in suppressing the mosquito population."
The agency has also shared data on areas with relatively higher Aedes aegypti mosquito population since late 2019.
There was also an expansion of NEA’s efforts for Project Wolbachia. Project Wolbachia involves infecting male Aedes aegypti mosquitoes with the Wolbachia bacteria, so that when it mates with a female, the eggs will not hatch. Male Wolbachia-infected mosquitoes also do not bite.
In February 2020, NEA expanded the ongoing field study at the Tampines and Yishun study sites to cover a total of 56,000 households.
“The results of the project thus far show more than 90 per cent suppression of the urban Aedes aegypti mosquito population at the study sites.
“NEA aims to expand male mosquito releases for Project Wolbachia – Singapore to more neighbourhoods over the next few years.”
To achieve this, NEA has established a new facility to allow researchers to eventually increase its production capacity of Wolbachia-Aedes aegypti mosquitoes by more than 10-fold, compared to the previous production facility.
At the same time, NEA advised residents on how to prevent dengue. This includes applying insect repellent, spraying insecticide in dark corners of the home, ensuring there is no stagnant water at home if leaving home for prolonged periods and seeking medical treatment early if they spot symptoms of dengue, like severe headache and high fever.