Source reduction is key strategy to fight Zika and dengue: Masagos

Source reduction is key strategy to fight Zika and dengue: Masagos

Between January and July this year, NEA conducted about 748,000 inspections to uncover mosquito breeding habitats and more than 10,000 breeding habitats were destroyed, says Environment and Water Resources Minister, Masagos Zulkifli.

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SINGAPORE: The National Environment Agency (NEA) conducted about 748,000 inspections to uncover mosquito breeding habitats between January and July this year and more than 10,000 breeding habitats were destroyed during these inspections, said Minister for Environment and Water Resources Masagos Zulkifli in Parliament on Tuesday (Sep 13).

Of the 10,000 breeding sites that were destroyed, about half of them were found in homes and about five per cent were in construction sites, said Mr Masagos in his ministerial statement as he outlined strategies to tackle the Zika outbreak in Singapore.

Besides deploying some 850 officers to do inspections island-wide, Mr Masagos said NEA also conducts indoor spraying with insecticide and outdoor fogging within the cluster to kill adult mosquitoes, as well as oiling of breeding habitats to kill any mosquito larvae.

“Zika and dengue are conveyed by the same mosquito – the Aedes aegypti. Our key strategy for dengue control, and now Zika, is source reduction – the detection and removal of breeding habitats and larvae,” said Mr Masagos.

"This integrated vector management strategy is in line with the World Health Organisation (WHO)’s recommendations and remains especially critical now as we are in the traditional dengue peak season," he added.

But Mr Masagos also noted that it would not be wise to conduct fogging indiscriminately outside of the clusters as a preventive measure. That is because fogging is only effective if the chemical has direct contact with the mosquitoes, Mr Masagos explained.

"The overuse or indiscriminate use of chemical treatment may cause the build-up of resistance in the local mosquito population. Fogging should only be used when there are Zika or Dengue clusters or when the adult mosquito population is observed to be high so that we can mitigate the situation quickly," he said.

Enforcement actions and penalties have been stepped up over the years at construction sites, Mr Masagos added.

Between January and July this year, the NEA issued around 50 Stop Work Orders for work sites repeatedly found with poor housekeeping and mosquito breeding habitats. A total of 410 notices were issued to construction companies to attend court and 40 errant contractors were prosecuted for repeat offences.

Even as the NEA has given attention to construction sites, Mr Masagos stressed that a large number of mosquito breeding sites is in fact found in homes.

About 2,200 households were fined between January and July this year as they were found to have mosquito breeding sites.

To mitigate the risk of transmission, the Government has also put in resources for surveillance.

NEA has deployed about 37,000 Gravitraps around Singapore and the number is set to reach 48,000 by the end of the year, said Mr Masagos. Gravitrap allows the authorities to identify areas with a large Aedes aegypti population and take targeted mosquito control measures proactively even if there are no dengue or Zika cases reported.

“This sort of risk-based, preventive surveillance work will go on well ahead of any peak transmission season,” Mr Masagos added.


Several MPs including MP for Holland-Bukit Timah GRC Mr Christopher De Souza, Non-Constituency MPs Mr Dennis Tan and Associate Professor Daniel Goh asked about what steps have been taken by the Government to contain the Zika virus.

In response, Mr Masagos said the current mosquito control strategy has helped suppress dengue over the years and the same strategy has prepared Singapore well to tackle the Zika challenge.

He added that following the Ministry of Health’s announcement of the first locally-transmitted Zika case on Aug 27, around 300 NEA officers, contractors and volunteers have been carrying out vector control efforts and outreach in the affected clusters.

As of Sep 11, more than 31,000 premises in the various Zika clusters have been inspected for mosquito breeding.

“In the Zika clusters, thermal fogging outdoors and indoor spraying of premises have been carried out to kill adult mosquitoes and the drains have been flushed to remove any stagnant water as an added precaution,” said Mr Masagos.

The NEA has also inspected construction sites and workers’ dormitories in the Zika clusters.

A Stop Work Order was issued to the construction site at Sims Drive on Aug 27 to curb the local Zika transmission as the site had failed to maintain satisfactory housekeeping and to eliminate potential mosquito breeding habitats, said Mr Masagos.

Mr Masagos added that the NEA has been working regularly with the Singapore Contractors Association (SCAL) to remind its members to be more vigilant about mosquito control and to look out for any workers with Zika symptoms.

Stricter requirements have been imposed on four dormitories. They are required to check for mosquito breeding and carry out thermal fogging if the mosquito population is high, as well as mandatory residual spraying in their premises on a quarterly basis.


Despite all these efforts, Mr Masagos told the House that Singapore remains vulnerable to dengue and other mosquito-borne diseases for a few reasons.

He cited that Singapore is in a dengue-endemic region and there are four different dengue virus serotypes circulating concurrently and a change in the predominant virus is usually followed by a spike in dengue cases.

The region’s warm climate and high humidity have also supported faster breeding and the maturation cycle of the mosquitoes, said Mr Masagos, adding that these have led to a higher mosquito population and the spread of diseases.

Mr Masagos also cited a large proportion of Singapore's population is susceptible to dengue due to the lack of immunity,

"In many other countries where dengue is endemic, the affected are often children. This is not the case in Singapore, which is good. Our success has, therefore, paradoxically lowered our herd immunity so that disease transmission occurs easily even with a very small mosquito population," said Mr Masagos.

“We must acknowledge that all these extraneous factors make it impossible to eliminate the Aedes aegypti here. Indeed, if we had done anything less, dengue and Zika would have spread throughout the whole island more quickly and thoroughly,” Mr Masagos added.

Mr Masagos stressed that everyone has a part to play in fighting Zika and dengue.

“Everyone – the Government agencies, premises owners, businesses, residents, and the community – has a role in our fight against Dengue and Zika,” he said.

Source: CNA/jq