Saturday, 9 January 2016

Dengue infections will be high this year, warns NEA

NEA expects spike in dengue cases this year
Factors include high base of cases, change in dominant strain and rise in mosquito numbers
By Salma Khalik, Senior Health Correspondent, The Straits Times, 9 Jan 2016

The battle against dengue could turn grim this year.

Not only is the number of infections expected to be large, but the cases are also expected to spike earlier than in previous years, the National Environment Agency (NEA) warned.

This is due to the confluence of three factors: Large numbers of infections in what is usually the low season, increases in the mosquito population and a change in the dominant viral strain.

The agency said on its website: "We are starting off the year with an unusually high base of dengue cases; 459 cases were reported in the final week of 2015."

This was the highest for the year. Between Sunday and 3.30pm on Thursday (latest availabe figures), there were 345 cases, signalling another week of high infections. Since 2013, Den-1 had been the dominant virus spread by the Aedes mosquito, accounting for more than half the infections. But now, more than two-thirds are due to the Den-2 strain, which marks a significant shift.

NEA said that, from historical trends, such changes in dengue strain "signal (a) possible spike in dengue cases".

On top of that, it added: "We have also seen a further increase in the Aedes mosquito population due to the slightly warmer than usual year-end weather."

It concluded: "The number of dengue cases in 2016 is expected to be high, with cases spiking earlier than in previous years."

Yesterday, Mr Masagos Zulkifli, Minister for the Environment and Water Resources, visited Singapore's biggest dengue cluster, where 195 people have been infected. It is in his constituency of Tampines GRC.

He said NEA found 86 breeding sites in the cluster. Of these, 60 were in homes, and only one at a construction site.

Of the 195 cases in the cluster, 81 are foreigners working at the Downtown Line 3 construction site, and the rest are residents. Some of the problem areas include Tampines Avenue 4 with 82 cases, and Tampines Street 91 with 24.

Calling out to dengue fighters in Tampines! Let’s work together to bring down the number of cases in your neighbourhood....
Posted by Stop Dengue Now on Friday, January 8, 2016

In his Facebook post, Mr Masagos said: "We found adult mosquitoes and larvae in some of the Gravitraps, indicating a high level of mosquito activity, despite three rounds of home inspections and destruction of breeding habitats.

"We need to prevent mosquito breeding. But NEA officers and town councils cannot achieve this alone."

More than 11,200 people were diagnosed with dengue last year, with four dying as a result.

NEA officers carried out more than 1.4 million inspections last year and found 15,000 breeding spots.

The agency issued more than 900 notices to construction sites to attend court, with over 100 prosecutions for repeat offenders.

It also issued more than 100 stop-work orders to construction sites.

It advised people living in active dengue clusters - there are 115 now - to use repellents to reduce their risk of getting the virus.

Singapore studying new way to keep dengue at bay
Method uses Wolbachia-infected mozzies to breed with females, which lay eggs that do not hatch
By Carolyn Khew, The Straits Times, 22 Jan 2016

While experts agree that genetically modified (GM) mosquitoes could help to suppress the wild mosquito population here, questions remain as to how well this approach would work in the long run and the Government is trying out another method to keep the insects at bay.

GM mozzies have a gene which prevents them from growing to adulthood and seems to have worked well in keeping dengue in check in several cities in Brazil.

This gene, however, is silenced if the insect comes into contact with the common antibiotic tetracycline.

In Singapore, the National Environment Agency (NEA) is, for now, studying the viability of using Wolbachia-infected mosquitoes instead. This method uses male Aedes aegypti mosquitoes infected with the bacteria to mate with the female dengue-spreaders, which then produce eggs that do not hatch.

The NEA told The Straits Times that its Environmental Health Institute had previously studied the GM mosquitoes produced by Oxitec, but the results were "inconclusive".

"For the progeny from the GM cross, they are not viable provided there is no tetracycline in the environment. For the progeny from the Wolbachia cross, the eggs do not hatch because they are unable to develop in the first place," explained an NEA spokesman.

"Another key difference is that the Wolbachia-Aedes technology is based on a naturally-occurring bacteria, which is found in more than 60 per cent of insects."

Oxitec pointed out that tetracycline degrades rapidly and that studies have shown it does not occur in sufficient amounts in the environment to impact the mosquitoes.

Dengue expert Duane Gubler, epidemiologist at Duke-NUS Medical School's Programme on Emerging Infectious Diseases, said that while the GM mosquitoes have very good potential to suppress the wild mosquito population, continual release would be needed to keep the numbers low.

"The Wolbachia virus takes a longer time to establish itself in the wild population, but once it does, it makes the mosquito less susceptible to dengue, chikugunya and yellow fever," he said. He added that both methods could be used in tandem, with the GM insects helping to suppress the wild population first, before the Wolbachia-infected mosquitoes are released.

Professor Annelies Wilder-Smith, who studies infectious diseases at the Lee Kong Chian School of Medicine at Nanyang Technological University, said that Singapore is understood to have low levels of mosquito infestation - except in areas where they are hard to eliminate, such as breeding places inside homes or construction sites.

"We have been fighting dengue in the same way for the last 100 years - by destroying breeding sites and spraying insecticides. And it hasn't been working very well... We need new tools and I believe the use of GM mosquitoes brings hope."

Any method that works to control mosquitoes should be welcomed, but with GM organisms, there are concerns over the potential ecological impact and risks, noted Dr Tikki Pang, visiting professor at the Lee Kuan Yew School of Public Policy at the National University of Singapore, who was director of research policy and cooperation at the World Health Organisation from 1999 to 2012.

"The big advantage is that the Wolbachia method does not involve genetic modification and, therefore, may be more acceptable from a public perception and risk perspective," he said.


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