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 shock syndrome, 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.

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.

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.