Stopping dengue : Rethinking our strategies

main_mosquito_1Dengue infections has been on the rise. Despite decades of experience with this virus, Malaysia is nowhere near getting on top of the situation. Perhaps rethinking the strategies may be wise.

Vector control

This has been the main strategy employed by public health in battling the spread of dengue. Putting Abate in breeding spots to destroy mosquito larvae and spraying insecticides to kill adult mosquitoes has been a constant feature in many areas designated as hot spots for dengue. There are concerns that mosquitoes are developing resistance to conventional insecticides.

Identifying these hotspots is reliant on reports from dengue cases in hospitals. It is compulsory for hospitals and clinics to notify health authorities of any cases of dengue. With the presumption that Aedes mosquitoes fly within a 50-100 metre radius from the source (patient), containment of aedes mosquitoes is concentrated as such. However, research has shown that a female mosquito can cover up to 840 metres from the source to lay its eggs. (Reiter et al, SHORT REPORT: DISPERSAL OF AEDES AEGYPTI IN AN URBAN AREA AFTER BLOOD FEEDING AS DEMONSTRATED BY RUBIDIUM-MARKED EGGS ,Am. J. Twp. Med. Hyg.. 52(2). 1995, pp. 177-179)

So perhaps we have underestimated the flying range of infected mosquitoes in considering our public health strategies. We also need to liase with entomologists in identifying if our mosquitoes are indeed developing resistance to our usual insecticides.

Campaigns to keep our drains and surrounding areas free of mosquito breeding spots need to be continuous. Aggressive monitoring of high risk areas, for example, construction sites, factories and squatter areas, need to be employed. Heavier penalties also need to be meted out, if we are to send a deterrent to harbouring aedes mosquitoes. Our education system needs to incorporate and inculcate knowledge of tropical diseases prevalent in Malaysia, in particular dengue.

Bio-engineered mosquitoes

Bio-engineering mosquitoes must be continuously considered. To our knowledge, there has been experiments in several areas where genetically engineered mosquitoes were released to mate with female mosquitoes in the wild. The offsprings are supposedly to live a shorter life and therefore be of no threat to humans.

There was also an experiment involving a bacteria infected mosquito (Wolbachia). Female mosquitoes infected with this genus of bacteria is unable to produce offpring. This will then control the mosquito population in dengue infested areas.

There are of course a lot of resistance from environmental groups who are concerned that bio-engineered mosquitoes can alter the delicate balance of the ecosystem. This is unsubstantiated and may be a viable option in the current epidemic scenario.

Dengue Vaccine

Finally there is the dengue vaccine. There is currently no approved vaccine. Prior trials have not conferred immunity to all serotypes of dengue virus. Trials are continuing in this area.

The Future

Newer immunological pathways are being explored in the case of dengue infection. As a greater understanding emerge, there is a likelihood that this infection can be stopped before it does damage to the body. However, it is likely not in the next few years and many more will likely die as a result. Even if a vaccine is available, it will likely be costly and its long term effects may continue to fuel debate on its safety.

As for now, low tech approaches are likely best. It needs to be continuous with the same intensity for long periods, if we are to ensure any impact on the control of dengue infections.

Bio war against dengue – The Star

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2 thoughts on “Stopping dengue : Rethinking our strategies

  • February 9, 2014 at 6:40 am

    Various strategies have been considered in tackling the Aedes/ Dengue phenomenon, although the public is less aware of it. For a start,the public health team involves entomologists in their vector-control, instead of doctors to decide on the strategy, as you know, doctors are more knowledgeable in human anatomy only, after all. The vector-borne control disease unit is a multidisciplinary team consisting of public health specialists, entomologists, health investigation officers, as well as our field “troops” who does the groundwork risk assessment, inspection and fogging when required.
    Not only that, there is also liasion with other units, which includes the law and inspectorate unit, health educational unit, as well as local councils in tackling the root of the problem, cleanliness, awareness and even structural flaws which may contain water suitable to breed mosquitors, such as Astro satelite dish. Community leaders and joint management board are called upon to raise awareness and remind the community to do their roles in preventing Aedes prevention.

    The minimum 200 up to 400 meter-radius coverage is an average estimated by entomologists’ studies including the behavioral flight pattern of Aedes mosquitoes which travel nearer when the food source is readily available nearby, hence laying groundwork to the basis of vector-control activities. In fact, there are more than 5 research arms in IMR ongoing researching on various aspects, including Aedes behaviour and resistance, serotyping, detection tests, vaccination and even biological and chemical controls. While it is ideal to cover as far as possible, just like on medicine, we have to take into account of the resources, just like the NNTI (Number needed to treat index) figures used in medicine.

    As for the fogging insecticides, there are various chemicals used and even on rotational basis to prevent resistance. However, just like any antibiotics, if the source remains, even the use of multple agents will lead to eventual resistance, hence the need for source reduction, which is the destruction of Aedes breeding sites.

    Bioengineered mosquiotoes are not only meeting resistancce from environmentalists, but from financial constraints. Each sterie bioengineered mosquitoes are to cost at least RM100 each and a large number need to be released into the environment while the results are unproven in urban settings especially in high rise settings (Mid you, most research are done in the open field settings or low density areas)

    Other new trial methods are done in small areas as they are yet to be proven effective to control epidemic, including deployment of various autocidal ovitraps, space-spraying of termephos at concentration adequate to even kill adult mosquitoes (Termephos are usually put in water to prevent breeding of Aedes larvae), space-spraying of BTI to reach areas difficult by conventional methods to prevent breedingof Aedes and even complex control of area coverage are eployed in the year 2014 by the Ministry of Health. All this are aimed to reduce the source.

    But why the source, one would ask? An adult Aedes mosquito can live on average 1-2 weeks, perhaps some extreme up to 3 weeks. While it takes up to 1 week for new adult mosquitoes to hatch from its larvae. However, the eggs could live up to 6-9 months even without water. So, that means that you would need to fog every week to kill off every adult mosquitoes in an area for up to 9 months to ensure that not even the last straw of eggs made it to breed for any generation. That amount of poison, would have been enough to cause serious ecological effects, as well as the human beings. Fogging is preferably done if there is an outbreak as a temporary measure while efforts to seek and destroy the Aedes breeding sites are made. Hence, the public perception should be change in that source reduction should be the solution to reducing Aedes mosquitoes, not fogging alone.Various campaigns have been run just to correct the public perception who would rather choose fogging out of convenience, to remind them of the current danger that Aedes would have pose without eradicating the source.

    For more information, do visit for more information. Ministry of Health are intensifying the health education and awareness as the vector-borne disease control unit had been doing work under radar for far too long that nobody knows its existent despite working 24/7.

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