Straits Times Forum 17 Jun 13;
WE THANK Mr Lim Boon Hee ("Dengue epidemic: More aggressive measures needed"; last Tuesday) for his interest.
The National Environment Agency's (NEA's) Environmental Health Institute is actively monitoring the development of new technologies in vector control, and evaluating the applicability of each technology in the context of our highly urbanised environment.
Mr Lim refers to trials on genetically manipulated mosquitoes, such as the one from Oxitec UK that releases sterile male Aedes mosquitoes to mate with females in the field, and causes a population reduction as the progeny will not mature to adults.
Thus far, preliminary results from field trials suggest some level of success in population suppression.
However, its impact on dengue transmission has not been demonstrated and our unique circumstances (highly urbanised environment, comparatively low levels of adult mosquitoes, and low herd immunity to dengue) requires careful evaluation to ensure such novel approaches can achieve a demonstrable impact on dengue, without negatively impacting our natural ecology.
The NEA advocates source reduction and the removal of potential breeding habitats through environmental management. In areas that cannot be reached, the NEA has been using Bti, a bacteria toxin that kills mosquito larvae.
The use of certain species of fish to eat up mosquito larvae was also raised by Mr Lim.
This is common in places where rainwater is collected in big pots for domestic use in lieu of piped water.
However, its use is not feasible in Singapore except in ponds. It is difficult to maintain a population of fish in our drains, as they are designed to channel water into our canals, water catchments or to the sea, and water found in drains is thus relatively transient.
We have also recently shared our stepped up efforts to address the dengue situation, such as eliminating adult mosquitoes through the indoor application of insecticides.
We will continue to monitor the progress of these novel technologies through close collaboration with the research community.
As the majority of breeding spots are found in homes, we encourage the community's concerted action to remove mosquito breeding habitats.
Ng Lee Ching (Dr)
Director, Environmental Health Institute
National Environment Agency
More aggressive measures needed
Straits Times Forum 11 Jun 13;
I SUGGEST that the National Environment Agency (NEA) implement other methods, such as biological control measures, to control the present dengue epidemic.
The current system of fogging and eradicating breeding grounds seems to be ineffective, if the 9,000 cases and two deaths are any indication ("60-year-old man 2nd person to die of dengue this year"; yesterday).
Malaysia mated genetically engineered Aedes aegypti male mosquitoes with females to produce no offspring or ones with shorter lives, in hopes of curtailing the mosquito population. Only female Aedes aegypti mosquitoes spread dengue fever.
Genetically altered sterile male mosquitoes were also set loose by scientists in a 40-acre region in the Cayman Islands between May and October 2010. By the end of the trial, mosquito numbers in that area dropped by 80 per cent compared with a neighbouring area where no sterile mosquitoes were released.
Releasing guppies is also an effective biological agent used in India to control mosquitoes in different habitats.
These fish have adapted to the sewage drain conditions and are involved in regulating the populations of different species of pest and vector mosquitoes.
The NEA has to be more aggressive in its fight against dengue fever. It should consider using biological agents to control Aedes mosquitoes as the present control measures appear to be ineffective and inadequate.
Lim Boon Hee
