Dr Leong Hoe Nam
Infectious Disease Physician
Pronounced dan-gee, dengue fever is a debilitating mosquito-borne viral disease in the world. Approximately 390 million dengue infections occur every year, with as many as 96 million resulting in illness.
Closer to home, neighbourhoods are labelled green, yellow and red zones to reflect the increasing risk of dengue fever respectively.
"Dengue fever is widespread in Singapore and in the region of Southeast Asia. The prevalence of the virus is closely tied to the prevalence of the Aedes mosquito, the transmitter of the infection," explains Dr Leong Hoe Nam, infectious disease specialist at Mount Elizabeth Novena Hospital.
Here's a comprehensive guide to help you understand the illness and gear up against the disease.
Dengue fever, also known as breakbone fever, is a vector-borne disease transmitted by the bite of an infected female Aedes mosquito. It can be caused by 4 different strains of the same virus (DEN-1 to DEN-4).
Dengue fever can vary from mild, presenting just as fever, to severe. Severe forms include dengue haemorrhagic fever and dengue shock syndrome, all of which are potentially lethal.
An overwhelming 75 – 90% of patients acquire dengue fever without any symptoms, not even fever. This means that many individuals who fall ill during their '1st symptomatic dengue fever' in fact had their 2nd attack. "It has been observed and hypothesised that 2nd attacks of dengue tend to be severe," says Dr Leong.
Dengue is prevalent throughout Southeast Asia and the western Pacific islands, but the disease has been spreading rapidly in Latin America and the Caribbean. Nonetheless, regardless of geographical location, dengue outbreaks can occur anytime and anywhere as long as warm weather conditions favour mosquito survival and the mosquitoes are active.
"In line with global warming, we see the widening and spreading of the footprint of the vector Aedes mosquito," says Dr Leong. "This, in turn, has led to the spread of dengue worldwide. We have seen reports of dengue in Italy and the Mediterranean countries, as well as in Florida, USA, during summer months."
In a nutshell, the Aedes mosquito can fly up to 400 metres looking for water-filled containers to lay their eggs but will usually remain close to human habitation. It prefers to breed in clean, stagnant water that's easily found in our homes. A volume of clean water that approximates a Singapore 20 cent coin is sufficient for breeding.
Dengue fever cannot spread directly from person to person, but a person suffering from dengue fever can infect mosquitoes. A mosquito becomes infected when it takes a blood meal from a dengue-infected person, and dengue spreads when the mosquito later transmits the virus to other people they bite.
"After 5 – 14 days, the virus will mature in the salivary glands of the mosquito and spread to the next victim during the mosquito's next feed," explains Dr Leong.
Humans are known to carry the infection across borders or from an area to another during the stage when the virus circulates and reproduces in the bloodstream.
In fact, the general belief was that the Japanese occupation of Southeast Asia during World War 2 provided the means for the growth and spread of the mosquito, and hence the virus in our region. The mosquitoes followed the troops that provided the breeding water and feeds for the mosquitoes.
Dengue fever presents itself with flu-like symptoms that typically show about 1.5 – 10 days after being bitten by an infected mosquito. If it's a mild case, symptoms will resolve on its own within 2 – 7 days.
The 1st symptoms include fever, headache, muscle and joint aches, high fever, pain behind the eyes, and vomiting or nausea. "Body rash tends to occur a bit later in the illness," says Dr Leong. "The absence of rash was identified to be a risk factor of severe dengue, largely due to a failure to recognise the illness."
Severe dengue develops 3 – 7 days after the 1st signs of illness with worsening symptoms, such as severe abdominal pain, persistent vomiting, bleeding gums, vomiting blood, rapid breathing, and fatigue or restlessness.
"One peculiar feature of the infection is that it can cause platelets (tiny cell fragments that form blood clots to stop bleeding) to fall steeply, which leads to bleeding in the internal organs, particularly in the gastrointestinal tract," explains Dr Leong.
Younger children and people who have not had the infection before tend to have milder cases than older children and adults. However, serious problems can still develop. These include dengue haemorrhagic fever (DHF) that may later progress to massive bleeding, shock and death, a condition known as dengue shock syndrome (DSS).
People with weakened immune systems, as well as those with a 2nd dengue infection are believed to be at greater risk of developing DHF. "Professor Scott Halsted, a leading figure in dengue research, popularised the belief that the 1st infection primes the body for a more severe 2nd infection," explains Dr Leong. "However, as we understand more of the disease, scientists have come to observe that the 3rd and subsequently 4th dengue infection may instead be less severe!"
If you're returning from an area where dengue is prevalent, you should consult your doctor before symptoms begin to show in order to get a peace of mind.
The symptoms of fever, headache, muscle aches, are overwhelmingly similar to other common ailments such as influenza, Chikungunya and Zika infection. In general, we recommend going for a blood test on day 3 of the illness to diagnose the disease.
Avoid dengue fever by preventing mosquito bites. Use a mosquito repellent, wear long pants, a long-sleeved shirt and socks. At home, install structural barriers.
The best protection is to avoid getting bitten by mosquitoes. The chances of being bitten are significantly reduced if you expose as little skin as possible. When in an area with mosquitoes, wear long pants, a long-sleeved shirt and socks.
Also, use a mosquito repellent with at least 10% of diethyltoluamide (DEET), a substance that repels biting pests. A higher concentration of DEET is necessary for longer lengths of exposure but avoid using DEET on young children. At the same time, avoid wearing heavily scented soaps and perfumes as these are known to attract mosquitoes.
At home, install structural barriers such as window screens or insecticide-treated netting. Nets that have been treated with insecticides are much more protective. Not only does the insecticide kill mosquitoes and other insects, it is also a physical barrier that prevents mosquitoes from entering the room.
Remember that the Aedes mosquito prefers to breed in clean, stagnant water in your home, so eliminate any possible breeding locations (eg. buckets, watering cans, receptacles). Practise the good habit of regularly cleaning and scrubbing your plant pots to remove mosquito eggs and loosen soil from potted plants to prevent puddles from developing on the surface of hard soil.
As of October 2016, the dengue vaccine Dengvaxia® has been approved by the Health Science Authority for the prevention of dengue disease in individuals aged 12 – 45 years. The vaccine has shown to be 70% effective in preventing dengue fever, and up to 95% in preventing severe, life-threatening dengue illness.
The World Health Organisation, in its expert panel review, recommended countries to implement a national vaccine programme using Dengvaxia® if the rate of previous dengue infection in their population falls below 50%. As such, the vaccine will be less effective here in Singapore. Individuals who wish to be vaccinated with Dengvaxia® should first consult a doctor.
Dr Leong recommends the vaccination for individuals who have had dengue fever before. This is especially important in preventing a second infection, which can often be more severe than the first.
70% of individuals have had dengue fever with no prior symptoms, ie. they had no idea that they had developed dengue fever the first time. For an accurate diagnosis of dengue fever, you can ask your doctor to perform the PanBio Dengue IgG Elisa test.
Diagnosing dengue fever can be difficult because its signs and symptoms are strikingly similar to other viral illnesses like influenza, Zika infection, Chikungunya infection, malaria, typhoid fever and so on.
In order for a doctor to properly diagnose dengue fever, they would assess the symptoms, take a blood test and assess your medical history. "During the acute illness, particularly on day 3, the dengue antigen NS1 is particularly sensitive and effective in diagnosing dengue fever," says Dr Leong. "On or after day 5 of illness, the dengue test for IgM/IgG antibodies would be a better tool in diagnosing the infection."
Your doctor may also ask about your travel history – be sure to describe internal trips in detail, including the countries you visited and the dates, as well as any contact you may have had with mosquitoes.
Dengue fever is caused by a virus, and there is no specific medication or antibiotic to treat it. For typical dengue fever, treatment is directed towards the relief of symptoms. Your doctor may advise that you rest and drink plenty of fluids to avoid dehydration from vomiting and high fever. Paracetamol can be taken to bring down fever and reduce joint pains but avoid pain-relievers that can increase bleeding complications, eg. aspirin, ibuprofen and naproxen sodium.
Do note that there are 4 strains of the dengue virus and once you recover from 1, you are unlikely to contract the same strain as your body would have built immunity against it. However, you may pick up repeated dengue fevers from the other strains.
Watch for the following warning signs of severe dengue:
"If you suspect that you have acquired dengue fever, start by drinking plenty of water. Adequacy of hydration can be assessed by the colour of the urine," Dr Leong advises. "We should aim for clear urine or those stained with a light touch of yellow."
Warning signs may appear as temperature declines 3 – 7 days after symptoms begin. Note that even though your temperature may decline, it does not necessarily mean you are recovering.
When warning signs of severe dengue are present, it is imperative to consult a doctor and seek hospitalisation to manage the disease. "Warning signs include severe abdominal pain, persistent vomiting, bleeding gums, vomiting blood, rapid breathing, and fatigue or restlessness," says Dr Leong.
"Should you suspect that you have acquired dengue fever, start by drinking plenty of water. Adequacy of hydration can be assessed by the colour of the urine," Dr Leong advises. "We should aim for clear urine or those stained with a light touch of yellow."
Dengue haemorrhagic fever (DHF) is a complication of dengue fever that tends to affect children under 10 years or age or older adults. DHF starts abruptly with continuous high fever and headache. Often, there are associated respiratory and intestinal symptoms such as sore throat, cough, nausea, vomiting, and abdominal pain. Shock occurs after 2 – 6 days if the patient remains untreated, and symptoms progress to a sudden collapse, cool and clammy extremities, a weak pulse, and blueness around the mouth.
In DHF, there is bleeding with easy bruising, red or purple blood spots on the skin, spitting up blood, blood in the stools, bleeding gums and nosebleeds.
"Rare but known complications of dengue include myocarditis (inflammation of the heart), resulting in severe and profound hypotension (low blood pressure), heart failure and damage to peripheral nerves," adds Dr Leong. "The latter persists for days to weeks after recovery with persistent numbness of the limbs."
Patients with DHF must be monitored closely for the 1st few days since shock may occur or recur unexpectedly. The mortality rate with DHF is significant. With proper treatment, the World Health Organisation estimates a 2.5% mortality rate. But without proper treatment, the mortality rate increases to 20%. Most deaths occur in children. Infants under the age of 1 are especially at risk.