Dengue facts, stats, strains, vaccines, symptoms and preventions
Singapore is one of the world’s safest cities, but we’re still not safe from dengue fever. This tropical disease may be deadly, particularly for young kids, but knowledge is power. With reports from the National Environment Agency of a spike in dengue outbreaks in Singapore (604 cases were reported during the week ending 9 January 2019), we decided to hunt down some facts, a few tips, and one kick-ass solution (scroll to bottom), so you can take the sting out of this insect infestation and turn it into a manageable situation.
1. Mosquitoes that carry dengue
The breed most responsible for the spread of dengue is infected adult Aedes aegypti mosquitoes. Their population has nearly tripled since the last major outbreak in 2013, according to the NEA. They are black with white stripes on their body and legs. It’s the females that bite, as they use blood to enable egg production. But let’s face it, if you’re close enough to see their colouring and sex you could be close to being a victim. It’s best to defend yourself against all mosquitoes and take preventative measures to avoid bites. Most importantly, people who acquire dengue fever need to prevent successive bites – if a mosquito that does not carry dengue bites an infected person and acquires the virus, they can become a carrier. And this is where the spread of dengue really gains momentum.
2. Behaviour of dengue-carrying mosquitoes
As if you didn’t already have ankle-biters to worry about – the Aedes aegypti mosquito is quite partial to biting around the feet too. Unfortunately, this can take place at any time of the day but peak hours are a couple of hours after sunrise and before sunset. They’re considered a domestic insect because they like hanging out indoors near humans. When resting, they are quite fond of dark and shady places like behind curtains, in wardrobes, under furniture and in corners. They like to breed in water so places where water is stagnant and can collect is the ideal home for larvae. Given the right conditions, an Aedes mosquito can hatch into larva in less than a day. By the same token, an egg can lay dormant for nine months in dry conditions and hatch when conditions are right again. The larva then takes about four days to develop into a pupa, and another two days to mature into an adult. Three days after the mosquito has bitten a person and taken in blood, it will lay eggs, about 100 of them, and the cycle begins again. This mosquito can lay eggs three times in its lifetime and its lifespan is about two weeks. If the mosquito happens to contract dengue by biting an infected person, then the results of this rapid breeding are dire.
3. Different strains of dengue
There are four different strains, or serotypes, of dengue and currently three of them are active in Singapore. This is a rare occurrence and a big reason why cases of infection have increased. Den-2 had been the main culprit for the spread of the disease for a while but, just like an ageing rock band that won’t die, Den-1 and Den-3 have recently had resurgence. This means that past sufferers, who would usually help to arrest the disease due to their increased immunity, have little defence against these previously dormant strains.
4. Dengue at its peak
Mosquitoes like to make hay when the sun shines. The hot dry months of May to October, in Singapore, are typically when dengue cases are more prevalent. The mosquitoes can breed and mature unimpeded at an accelerated pace. What makes this year a bit more concerning is that dengue epidemics tend to occur every five to seven years, with higher peaks recorded each time it returns, and we are now due to ride the crest of this wave. Although the number of people infected currently is significant, the number of people experiencing severe fever is considered low.
5. Trial of dengue vaccine
The results of a trial of the world’s first dengue vaccine have shown it capable of providing moderate protection against three strains of dengue, according to findings published by The Lancet Journal. The study found the vaccine reduced the most serious cases of haemorrhagic fever by nearly 90 per cent. However, protection for children did not prove very effective and it did not fare well against Den-2, our most common strain in Singapore. The results, from French producer Sanofi, suggest the new vaccine acts best as an immune booster for patients with some previous exposure to the virus.
6. Symptoms of dengue fever
The dengue virus is a mean little infectious agent and takes two forms. Dengue fever is the less vicious attacker but is no walk in the park. Symptoms include a fever that can last seven days, body aches and joint pain (which is where its other name, ‘breakbone’, comes from), intense headaches, vomiting, nausea, loss of appetite, dehydration, itching and skin rashes. Even when a sufferer is past the worst of it, it can take a month to recover from tiredness and being rundown. Dengue haemorrhagic fever shares all the same features, with the addition of a severe reduction in platelet count, blood vessel leakage, bleeding of the gums, nose, skin and internal organs and dangerously low blood pressure. Needless to say this can be life-threatening and treatment should be sought immediately.
7. Treatment for dengue fever
It’s important to visit a GP for diagnosis, then rest and drink plenty of water. A doctor should also be able to instruct if hospitalisation needs to take place. If symptoms already include stomach pain and vomiting, head to the hospital. There are no anti-viral drugs available but there a few things that doctors might prescribe to ease symptoms, such as folic acid for stomach bleeding and antihistamines for itchy skin. If dehydration is very bad, then intravenous fluids will need to be administered. If platelet count gets very low, then there might be a need for blood transfusions.
8. Preventing dengue infection
Prevention is the cure for now. Here’s what you can do:
Do the NEA 5-step mozzie wipeout:
- Change water in vases/bowls on alternate days
- Turn over all water storage containers
- Cover bamboo pole holders when not in use
- Clear blockages and put BTI insecticide in roof gutters monthly
- Remove water from flower pot plates on alternate days
You may also find it useful to refer to their checklist for houses and condos.
Contact the NEA
We’ve had first-hand experience dealing with these guys and can’t speak of them highly enough. After sending off an email to inform that there seemed to be a few more mozzies in our area than normal, the NEA had contacted us and deployed a crew to our home within 24 hours. An extremely thorough inspection was carried out and neighbouring properties were also visited. Some traps consisting of carbon dioxide tablets, designed to attract and kill mosquitoes, were inserted into drains for good measure. We even got a follow-up call a few days later to say they had discovered a breeding ground nearby and had destroyed it. So, big thumbs up, NEA!
Apply insect repellent
- DEET – The most common active ingredient for repellents in Singapore is DEET, in concentrations from seven to 25 per cent. Typically a higher concentration indicates longer-lasting protection, not a reduction in your chances of being bitten. Studies suggest it is safe for children in lower concentrations but not for infants under two months of age. A reliable option is the RID range from Australia, available at International Medical Clinic. IMC carries the Tropical Strength range (six hours’ protection), the low irritant Kids RID, which is suitable for children over six months of age (two hours’ protection), and an SPF 30+ sunscreen/repellent combination.
- Permethrin – Permethrin is a naturally occurring insecticide, which can be used safely to treat your baby clothes. It’s a good option for children under six months old. IMC stocks Permethrin Treatment Kits.
- Natural – There are a number of natural alternatives available. Products that contain citronella, such as Badger Anti-Bug Balm, have shown to be effective and are safe to use all over the body. You will need to re-apply more often though.
For more product options check out the selection at RedMart.
Burn citronella oil
Burning candles containing citronella can reduce the chance of being bitten somewhat. In fact, any candle may help, although what the mosquito is avoiding is the smoke, not just the citronella. You do need to be safety-conscious though – effectiveness improves the closer you are to the flame and smoke. You can also pick up citronella essential oil from iHerb if you prefer to use a burner. Mosquito coils are considered questionable due to the fact that the smoke they produce, from sometimes-unregulated ingredients, can be harmful to respiratory function.
Use mosquito nets
Although a mosquito net might not be that useful at night, it’s a good option for protecting sleeping babies during the day when Aedes aegypti mosquitoes are out feeding. It’s worth noting though that there are some safety risks involved: IKEA withdrew their netted bed canopies for children recently amid fears of strangulation. Spotlight sells bed canopies and mosquito nets and The Australian Mosquito Net Shop, who ship internationally, has a model that fits over cots and can then be suspended to extend over beds as children grow.
If you live in a condo, this probably already takes place once a week. If you live in a house you can organise to have it done but it’s really only effective if it takes place on an ongoing basis due to the lifecycle of the mosquito. There is a lot of controversy surrounding fogging and DDT due to the side effects of insecticides and diesel and the negative effect they can have on the environment.
Research mosquito traps
Mosquitoes are attracted by sight and smell, so lights and carbon dioxide are the common lures used to trap them. Because the Aedes aegypti mosquito is active during the day, they are quite responsive to visual attractants. Most traps you can buy use a combination of both of these elements and when the mosquito gets close a fan sucks them in and catches them in basins, sticky mats or bags. Generally it can take about two months to wipe out enough females for the local population to collapse.
The principle behind a trap is to act as a screen, so their placement is crucial. They need to be positioned between the source of mosquitoes and where people gather. The effectiveness of them is therefore debatable – they will certainly kill the ones that they trap but the issue is getting them to the trap site. Online reviews point to the Mega Catch Ultra as the most effective trap on the market currently. You can source them from Mosquito Management System here in Singapore.
In our experience, the options you can get at HomeFix and other small hardware stores baffled us as the store staff don’t seem to be that informed about the products. One last thing on traps: the internet is awash with homemade mosquito trap guides, but because liquid is usually involved be careful you don’t go causing an infestation rather than preventing one.
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