Dengue wants to be your new boyfriend/girlfriend, but it'll be a terrible ex: S'pore doctor

The dengue virus infects humans, causing sudden fever, severe headache, joint and muscle pain, rashes, nausea, and in rare, severe cases, death.

Like with other viruses (e.g. Covid-19 or chickenpox), even though patients do develop some immunity from past infection, it is possible to get dengue repeatedly — up to four times.

This is why dengue can be like a terrible ex, says Leong Hoe Nam, a doctor who specialises in infectious diseases.

He also talks to Mothership about why it might be impossible for the mosquito-borne disease to be fully eradicated in Singapore, and what we can do about it.

Why is it possible to get dengue four times?

“There are four different types of dengue in the world,” says Leong.

They are known as DENV-1, DENV-2, DENV-3 and DENV-4.

Each of the types are sufficiently different that they can be considered different viruses, he explains.

And yet, they have very similar structures, such that the human body can get confused between the virus types.

This makes a dengue infection different from the usual scenario where those who are infected with viruses like Covid-19 or chickenpox can recover and gain some level of immunity against those viruses.

Someone infected with one type of dengue is actually more likely to be infected with one of the other types.

Thus, an infection with one type of dengue virus actually “enhances the infectivity” of the other types.

“The first infection disadvantages the infected individual for the second, because the body responses assume the second infection was the first, when it is different,” says Leong.

Thus, it is possible to get dengue four times as each virus is different. “The body has to develop a different immunity to the next strain,” he explains.

“So in theory you can have four encounters with the dengue virus because of the four strains circulating.”

How is this explained by the example of the “terrible ex”?

“For many of us, the second girlfriend or boyfriend relationship is modified by the experience of the first,” says Leong.

“But if you think about it, each potential lifelong partner is different from the previous boyfriend or girlfriend. Using previous experience to enter a relationship is the biggest disaster one can make.”

Leong says this is “exactly what happens with dengue”.

For a patient who has recovered from one type of dengue, their body’s natural reaction will be to use the prior experience of the first dengue to fight the second dengue.

But, because of the difference between the dengue types, the body’s experience dealing with the first type is not helpful at all.

“You make a mess of things,” says Leong.

What is it like getting dengue?

While the analogy of a terrible ex might be amusing to some, it’s a serious matter; a dengue infection can be quite debilitating.

“It would be seven days of misery, often described as being hit by a truck,” says Leong.

It can also have more severe consequences for those in vulnerable groups, such as the elderly and those with chronic illnesses.

For them, “it is akin to having a guillotine hanging over their neck until it is completely over,” Leong adds.

If dengue is so serious, what is being done to tackle it?

Leong explains that much of what is being done focuses on “reducing mosquito load” — targeting the vectors that transmit the virus.

For example, there are “aggressive hunts for breeding sites”, and carry out fogging operations (though Leong points out that sustained fogging may also have unintended consequences).

Leong also points to Singapore’s project to release male Wolbachia-Aedes mosquitoes to prevent mosquito breeding.

Aside from clearing breeding sites, education campaigns aim to rope in the public to clear stagnant water to prevent mosquito breeding at home and in common areas.

So when will we completely eradicate dengue in Singapore?

It may not actually be possible to totally wipe out dengue in Singapore.

“If you go to a dengue cluster area now, and you manage to catch every single aedes mosquito in the area, less than one per cent of the mosquitoes carry the dengue virus in the salivary glands,” says Leong.

To hunt down that small number of mosquitos in any given geographical area “is like targeting the needle in a haystack,” he adds.

“Clearing all mosquitoes is a pie in the sky,” Leong says.

Furthermore, doing so would be “a blunderbuss approach”, which would also be “inappropriate and wasteful”.

What if we somehow managed to catch all the dengue-carrying mosquitoes?

It’s also not possible to prevent dengue-carrying mosquitoes from entering Singapore. Leong says:

“Even if miraculously we do [catch 100 per cent of them], the mosquitoes can fly over and repopulate in a very short while, just like humans entering or leaving Singapore.”

So what are some dengue-prevention steps that Singaporeans can take?

While Leong says that dengue is “here to stay”, there are also “alternative defensive measures” that may be helpful.

Leong points out that a dengue vaccine could similarly “ameliorate the risk of severe infection”, just like vaccination against Covid-19 prevented severe illness in many individuals, even when the virus was actively circulating among the population.

But an effective vaccine would need to be tetravalent — that is, capable of targeting each of the four types of dengue.

Thus, a dengue vaccine that works well against all four strains of the dengue virus would represent a major advance for the control of the disease. It could be an important tool in the prevention of dengue.

There are in fact several vaccines in development, and you can read more about them on the World Health Organisation (WHO) website here.

In the meantime, Leong says Singaporeans who are concerned about dengue should participate in the mosquito eradication measures initiated by the authorities.

It’s not enough that we avoid creating breeding sites — we should go further and clear potential breeding sites when we see them.

He adds, “See any puddle of water, drain it and you drain the risk of mosquito breeding.”

This sponsored article by KnowDengue.sg made the author grateful he doesn’t have a crazy ex out there waiting to infect him.

Top image by Priscilla Du Preez and Ronald Langeveld on Unsplash