The silent assassin

The silent assassin

Thailand has seen a staggering rise in dengue infections, with more than double the amount of fatalities than all of last year

A Wang Thonglang district official sprays fogging chemicals in a residential area  in Soi Lat Phrao 69 on Lat Phrao Road in Bangkok to prevent the spread of mosquitoes that cause dengue fever. (File photo by Patipat Janthong)
A Wang Thonglang district official sprays fogging chemicals in a residential area in Soi Lat Phrao 69 on Lat Phrao Road in Bangkok to prevent the spread of mosquitoes that cause dengue fever. (File photo by Patipat Janthong)

The downpour that began late last month declares that Thailand has officially entered the rainy season. But it also serves as a warning sign to stay vigilant for dengue fever.

According to statistics from the Bureau of Vector Borne Disease under the Ministry of Public Health's Department of Disease Control, it seems this year the country has seen a staggering increase in the number of dengue cases. Only six months in, Thailand has over 26,000 infected cases with 41 deaths. These numbers suddenly become a national worry when compared to last year when a total of 14,900 infections and 19 deaths were reported.

Even in 2016, the year when Channel 3 actor Thrisadee "Por" Sahawong succumbed to dengue infection and died at Ramathibodi Hospital, Thailand only saw around 18,000 cases throughout the year. Only 16 deaths were reported.

Speaking ahead of Asean Dengue Day, which falls annually on June 15, Assoc Prof Dr Kriengsak Limkittikul, a virology expert from the Department of Tropical Paediatrics, Faculty of Tropical Medicine under Mahidol University, said that given the sharp rise with regard to dengue cases, it can be predicted that this year's outbreak is likely to be serious.

"Dengue fever has an outbreak pattern in which a huge outbreak usually hits every two to three years," said Dr Kriengsak. "Normally we'll look at the infection rate during the dry season before the rain comes. If the rate is high, it could possible mean that dengue fever is going to be an epidemic. More rain means more mosquitoes. If the infection is high even before it rains, the disease will easily spread."

Thailand is not the only nation that sees a worrying sign of dengue infection this year. Just recently, the World Health Organization (WHO) declared an unprecedented outbreak of dengue fever in the French overseas territory of La Reunion where tens of thousands of people were reported to have been infected. So far this year, around 22,000 people are suspected to have caught the disease on the popular Indian Ocean tourist island. Last year, only around 6,900 people were diagnosed with dengue fever.

According to the WHO, the number of dengue cases dropped globally in 2017-2018, but there has been a sharp increase this year, especially in Australia, Cambodia, China, Laos, Malaysia, Philippines, Singapore and Vietnam.

Dr Kriengsak said that better screening technology can be attributed to the rising statistics during the past few years.

"A dengue screening test called Dengue NS1 has been widely used lately and many times it detects a virus even without much symptoms. This could probably result in many more reported dengue cases," he said.

And thanks to media coverage during the past years, Thai people are more aware of the disease and its severity. Dengue infection can be deadly even among people who are physically healthy and can kill shortly after a patient is infected. With these scary facts, certain groups of people should be extra watchful as the rainy season kicks off to shield themselves and family members against the mosquito-borne infection, Dr Kriengsak said.

Yet despite better public awareness and understanding when it comes to the disease, there are still some missing pieces to the puzzle when it comes to curbing dengue infection in the country.

First, despite years of campaigns, dengue fever is still a big-city disease, which means it wreaks havoc more among urban populations than in rural neighbourhoods.

"Thailand has very strong public health volunteer networks in provinces where medical volunteers work hand-in-hand with community hospitals to get rid of mosquito-breeding areas, which is the most effective way to prevent dengue fever. But this is not the case in city areas where people sort of have distant relationships. When they don't know the person next door gets infected, they do not realise the severity of the disease and subsequently probably won't allow mosquito spraying in the neighbourhood."

"Especially Bangkok is full of skyscrapers and high-rise residences," he added. "Which makes it almost impossible to do mosquito spraying."

Second, it's a vaccine debacle. In December 2016, Thai people were thrilled by the arrival of a dengue vaccine that then promised around 93% efficacy in reducing the severity of the disease and over 80% effectiveness in lessening the need for hospitalisation.

But only a year later, study-based evidence was released and confirmed that the dengue vaccine could backfire. It was reported that the shot was ideal only for those who have been infected before. People who never had dengue and are vaccinated and later become infected may have a much more severe form of the illness.

In Thailand, the vaccine has been put on hold following the same decision by the Philippines Department of Health to suspend its mass vaccination programme in which more than 733,000 children were reported to have received the shot. Back then, the Paediatric Infectious Disease Society of Thailand also came out and advised people to stop receiving the vaccine.

"To understand the efficacy of the vaccine, it is very important to understand how the disease progresses," the virologist explained. "The first infection is usually not serious in terms of symptoms. Then the second infection is much more severe. After that the body is immunised so the third, fourth infection and so forth is nothing much to worry about. So the problematic period is between the first and second infection.

"Vaccination equates to being infected. If you never had dengue fever and you get a shot, that's the first infection. So when you are actually infected, that is the second infection and is likely to be severe."

Of course, the vaccine controversy has affected the reliability of the shot. But, according to Dr Kriengsak, it doesn't translate to the jab being all bad and harmful.

"There is no such thing as a magic bullet. The vaccine still has its role and is not completely useless. It's just that we have to give it to the right person, to use where and when appropriate," noted the specialist, adding that the dengue vaccine is ideal for people aged between nine to 45 and is administered as a three-dose series at six-month intervals.

While the vaccine loopholes wait to be fixed, Dr Kriengsak advised control of the mosquito population as the most effective protocol to curb dengue infection.

"For now, the best way is to prevent mosquito bites by implementing some basic measures such as wearing appropriate clothes, using mosquito repellents and so forth. Especially during rainy season, it is paramount to make sure to eliminate stagnant water to cut the breeding ground for mosquitoes. Also keep an eye on conditions such as high fever of over 39-40C, body pain and eye pain without coughing, sore throat and runny nose. If these conditions do not subside within a day or two, it is best to have a hospital visit.

"In terms of the vaccine, people can have it if they fall into an appropriate group and find the shot affordable. But for now, the vaccine is not the most effective prevention against dengue fever given its limitations. In the future, if there are more pharmaceutical companies that develop a new vaccine that overcomes the existing glitches, then that's another story to discuss."


  • Before 1970, only nine countries had experienced severe dengue epidemics. The disease is now endemic in more than 100 countries worldwide, with the Americas, Southeast Asia and Western Pacific regions as the most seriously affected zones.
  • It is estimated that 390 million people are infected with the dengue virus per year. Another study, of the prevalence of dengue, estimates that 3.9 billion people, in 128 countries, are at risk of dengue infection.
  • Severe dengue was first recognised in the 1950s during epidemics in the Philippines and Thailand.
  • There is no specific treatment for dengue or severe dengue, but early detection and access to proper medical care lowers fatality rates below 1%.

Information from the World Health Organization.

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