Bloody mosquitoes! How dengue virus spreads around the world

  • Wellness
  • Thursday, 29 Aug 2019

Mosquitoes filled with Wolbachia are ready for release in an effort to reduce dengue cases. — AP

I read about the recent rise in cases of dengue fever in Malaysia. How common is dengue fever around the world?

Dengue fever is extremely common around the world. The World Health Organisation (WHO) considers dengue fever as the most critical mosquito-spread viral disease globally. In the past 50 years, there has been a 30-fold increase in the number of dengue cases, with an estimated 390 million cases every year worldwide.

Within this number, half a million cases develop into the more dangerous dengue haemorrhagic fever (DHF), which can cause up to 25,000 deaths every year around the world.

Now I am scared! Which countries are dengue fever most common in?

Any country situated between 10° north and 10° south latitude is at risk. This includes tropical and subtropical parts of Asia (yes, Malaysia is definitely included!), Africa and South America.

How did dengue fever originally come about?

The first recorded case of dengue fever was found in a Chinese medical encyclopaedia from the Jin Dynasty, which was as far back as 265–420 AD! It wasn’t called dengue fever then; it was called “water poison” and was associated with flying insects. After that, there were probably many people who contracted and died of dengue fever, but it wasn’t described until around the 1780s.

American physician Dr Benjamin Rush coined the term “breakbone fever” in 1789. There were plenty of dengue epidemics then, which occurred almost simultaneously in Asia, Africa and North America. Dr Rush called it “breakbone fever” because the disease causes a lot of tiredness, back pain, joint pains and muscle aches. At that time, no one knew that dengue fever was transmitted by mosquitoes. This was only discovered in the 20th century.

How did dengue fever get to be so prevalent around the world?

Well, the disease spread further and further around the world. During World War 2, whole populations were affected because of so much movement between countries worldwide. Mosquitoes followed ships, airplanes and people around the world, and epidemics bloomed everywhere.

The first epidemic of DHF happened in Manila, the Philippines, in 1953. Following that, it became more and more common for countries to report outbreaks. In the late 1990s, dengue fever became second in frequency only to malaria worldwide, with 40 million cases reported of dengue fever alone.

As for DHF, they numbered in the hundreds of thousands. At that time, in the mid-1990s, I myself was among the casualties. I worked in a general hospital with an on-call sleeping room that was known as “the dengue room”.

It meant that whoever slept in that room while they were on call were 100% certain to contract dengue fever! I contracted the DHF type and was bleeding from my gums. My platelet count went down to 11 (the normal range is 150-400).

In the ward, we admitted so many dengue cases every day and monitored their platelet levels while providing supportive therapy. The moment the platelet levels went on the uptrend, we discharged them.

Significant outbreaks of dengue fever occur every five or six months. DHF outbreaks happen yearly. This pattern has repeated itself as dengue fever spreads to more and more areas.

I know about the anti-Aedes mosquito campaign run by Malaysia. Is there any treatment or vaccine for dengue fever?

There is no specific treatment other than observation, support with fluids (orally, and if necessary, intravenously) and providing IV (intravenous) platelets if the patient’s platelet levels get too low. In dengue fever, your platelet count is low because dengue fever is a viral disease that causes bone marrow suppression, reducing your ability to produce platelets.

Moreover, the dengue virus can bind to your platelets, causing them to be destroyed more easily. One dengue vaccine has been licensed, while a couple of others are undergoing clinical trials. However, researchers have found that where Wolbachia, a natural bacteria present in 60% of insects, is found, there is very little dengue virus present.

Wolbachia? This is interesting!

Yes. These bacteria are, unfortunately, not naturally found in the Aedes aegypti mosquito, which is responsible for transmitting the dengue, Zika, chikungunya and yellow fever viruses. Many scientists have studied these bacteria, looking for ways to control this deadly mosquito.

Research has been done on inoculating Aedes mosquitoes with Wolbachia. These Wolbachia-filled mosquitoes are then released into the wild for a few weeks so that they can breed with the wild mosquito population, ensuring that their offspring also have Wolbachia.

Over time, there will be more and more Wolbachia-carrying mosquitoes, which have a reduced ability to transmit diseases to humans. The mosquitoes are not altered genetically and Wolbachia is totally safe for humans and animals.

In fact, the Health Minister launched a programme to release Wolbachia-filled Aedes mosquitoes in Kuala Lumpur, Putrajaya and Selangor in July 2019, with plans to extend it to other states in September 2019. Hopefully, this will help usher in an era of reduced dengue fever.

Dr YLM graduated as a medical doctor, and has been writing for many years on various subjects such as medicine, health, computers and entertainment. For further information, email The information contained in this column is for general educational purposes only. Neither The Star nor the author gives any warranty on accuracy, completeness, functionality, usefulness or other assurances as to such information. The Star and the author disclaim all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.

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