Is dengue-3 dominant, more lethal?

Virologists and entomologists said it cannot be said conclusively that Denv-3 – one of the four serotypes that cause dengue fever – is dominant in Dhaka, or that it is more infectious and lethal as Bangladesh recorded 49 deaths from dengue this year until Friday.

A recent research suggested that Denv-3 is the dominant category among patients at a hospital in Dhaka. The researchers also attributed the widespread outbreak, higher fatalities and rapid health deterioration of patients to the virus type.

But virologists said there is not enough scientific evidence to fully support the findings since the research collected samples only from 20 patients from a single hospital.

Scientists at the Bangladesh Council of Scientific and Industrial Research (BCSIR), popularly known as Science Lab, on Sunday said the Denv-3 serotype of dengue virus is dominant in Dhaka now, and contracting the virus type with a previous infection history could be fatal.

According to the research findings, a second time infection with Denv-3 for people who previously got infected by Denv-1 and 2 could show symptoms such as bleeding, blood clots and abdominal pains. Their platelet counts also fall rapidly, putting patients in severe shock.

After getting infected by dengue once, BCSIR researchers said, patients can be infected again after a year as immunity wears out by this time. They also claimed dengue could be transmitted to children by breastfeeding.

BCSIR Principal Scientific Officer Salim Khan even told The Business Standard that there could be Denv-5 or Denv-6 in future.

'Totally a nuisance': Virologists debunk dengue myths

"You have to understand that serotype and variant are completely two different things. The prediction about Denv-5 or Denv-6 is completely a nuisance," Dr Jahidur Rahman Khan, virologist at Shaheed Suhrawardy Medical College, told TBS.

The term serotype is used to describe viruses of the same species that are antigenically different. Roughly a variant is a form or version of a virus that differs in some respects from other forms.

According to the World Health Organization (WHO), the virus responsible for causing dengue is called dengue virus (DENV). There are four DENV serotypes, meaning that it is possible to be infected four times.

Dr Khan said Denv-3 is not a newly found serotype in Bangladesh as it has been dominant in the country since 2002. "There was a pause for 10-12 years and then the prevalence of the serotype started to surge again after 2017," he added.

Is Denv-3 more lethal? In reply to the query, he said, "The fact is not that Denv-3 is more lethal than Denv-1 or 2. Basically, the Denv-3 serotype was not out there for quite a long time. Therefore, we do not have antibodies to fight against, leading to a rapid deterioration of patients' conditions."

He said if anyone gets infected by one serotype, he or she will be protected lifelong against that specific serotype, but not from the other three. Now if the individual gets infected for the second time by any of the three serotypes in future, the possibility of getting severely sick and death multiplies several times.

On the claim of BCSIR's Denv-3 dominating Dhaka, Dr Jahidur Rahman Khan said, "Research on only 20 samples cannot mention conclusively that Denv-3 is dominating Dhaka. No statistical structure for research can do that."

"But it is an important finding. We have to do more study with more samples from different sources."

Dr Manjur Ahmed Chowdhury, chairman of the Centre for Governance Studies (CGS) and an entomologist, also raised his concerns over the BCSIR sample size.

"Their sequencing for the research is appreciable. But the sample size is too small to make any comment about the findings," he said.

"The Denv-3 infection was also there in 2019. But what is concerning is the second time infection," Dr Manjur noted.

Expressing dismay at the BCSIR dengue remark on breastfeeding, Dr Rezaul Karim Kajal, gynaecology specialist and also a Bangabandhu Sheikh Mujib Medical University Hospital teacher, said, "Neither dengue nor Covid-19 can be transmitted to children by breastfeeding."

According to the Institute of Epidemiology Disease Control and Research (IEDCR), Denv-1 and Denv-2 caused the dengue outbreak in 2016 in Bangladesh. Denv-3 infection rang alarm bells in 2018. It turned into an epidemic in 2019.

255 hospitalised, one dies in past 24 hours

In the 24 hours till Friday morning, 255 dengue patients were admitted to hospitals across the country, with one patient dying, according to the health directorate control room.

The latest hospitalisation raises the dengue caseload this year to 11,236. As many as 7,698 people got admitted to hospitals with the mosquito-borne dengue alone in August. That is around 67% of this year's total caseload.

The country has logged 49 deaths so far, with August alone registering 33 fatalities.

According to the health directorate, 1,405 people were hospitalised with dengue in 2020 and seven patients succumbed to the infection.