In 2023, Bangladesh faced a significant escalation in the dengue outbreak, with a distressing 321,179 hospitalisations and 1,705 fatalities recorded from January to December. This represented a record high for dengue-related deaths in the country, with cumulative deaths for the year surpassing all totals of the previous 23 years (2000-2022: 853 deaths vs 2023: 1705 deaths).

Last year, it was from July that the cases really started spiking (43,854 cases), with hardly any deaths in the first six months. The highest number of dengue cases were recorded (79,598 cases) in September. The highest death toll was also recorded (396 people) in September 2023.

By comparison, 2024 has been relatively quiet on the dengue front, at least till September rolled around. At least 80 people died of dengue in September, making it by far the deadliest month this year in Bangladesh, according to the Directorate General of Health Services (DGHS).

On the last day of September, last Monday, the country reported five more deaths, bringing the total fatalities from the mosquito-borne disease in Bangladesh to 163 this year. As per DGHS, 14 people died in January this year, three in February, five in March, two in April, 12 in May, eight in June, 12 in July and 27 in August.

The sharp spike in September, although still not at the levels witnessed last year, is enough to set alarm bells ringing if the country is to avoid a high number of casualties in the remaining months of the year. Which itself is strange, since traditionally dengue has been a summer disease. But in the last few years we have seen it transform into a menace all year. Last year there were more deaths in the winter months.

Meanwhile globally, dengue cases have surged this year. More than 12 million cases and 6,991 deaths have been recorded globally till August this year, according to data from the WHO's global dengue surveillance. This is more than double the 5.27 million cases recorded in all of last year, which itself was a record. Prior to last year, over the past decade, around two to three million annual cases of dengue had been reported at best.

Experts say that even 2024's record numbers are likely to be an undercount. This is because not all countries report their data to the global surveillance network. Even among countries which report the data, not every dengue patient might have been tested and reported to the health authorities.

An editorial in The Lancet, the leading medical science journal, identifies "the triad of urbanisation, climate change, and the movement of people and goods" as facilitating the spread of dengue, and its mosquito vector.

The disease can spread more quickly in urban areas with a dense population. This is because urban spaces provide ample breeding grounds to the Aedes aegypti mosquito which breeds in clean, stagnant water. An increase in cases is generally reported during and just after the monsoon in the countries of South Asia.

An increase in temperatures allows mosquitoes to breed in places where they previously could not - in higher altitudes for instance. Moreover, climate change has also led to the virus becoming more robust and transmitting better. On the current outbreak, the US Centres for Disease Control and Prevention said: "Higher temperatures can expand the range of the mosquitoes that spread dengue, as well as affect other factors that facilitate virus transmission like faster viral amplification in the mosquito, increased vector survival, and changes in reproduction and biting rates."

The global movement of people and goods has, in general, led to a greater spread of infections that these people carry with them. However, better testing and reporting might also add to the increase in numbers recorded. Apart from dengue, other infections such as chikungunya and zika, which are also transmitted by the same vector, have also been on the rise.

Situation in Bangladesh

Fifty percent of the total hospitalised dengue patients are from the two city corporations of Dhaka followed by Chattogram and Barishal, according to the Directorate General of Health Services (DGHS).

According to DGHS, the dengue season began in July this year, resulting in 12 deaths and 2,669 infections. In August, the situation worsened, with 27 fatalities and 6,521 new cases.

From January 1 to September 25, among the 138 dengue-related deaths, 52.2% were women and 47.8% were men.

Prof. Kabirul Bashar, a Zoology professor at Jahangirnagar University, warned that the dengue situation is likely to worsen without special measures. "People are dying every day," he said.

"We have been warning for two months that the situation would deteriorate in September, but no one paid heed. Apart from regular operations, there has been a lack of targeted action during this peak period."

He noted that almost every year, a team from the health department reviews the dengue deaths. The primary goal of this review is to assess each case and determine ways to lower the mortality rate.

However, he expressed uncertainty about how much these death review reports are shared with researchers or policymakers. He emphasised that this information and data could significantly contribute to reducing the future mortality rate of dengue.

To effectively control dengue, he urged for evidence-based integrated mosquito management strategies and a shift from a job-oriented to a service-oriented mindset among responsible agencies.

"Under hotspot management, crash programs should be done within 200 metres of houses where there are dengue patients. Flying Aedes mosquitoes and larvae must be destroyed," the expert suggested.

Visiting Dhaka's Mugda Medical College and Hospital, it was found that this hospital has been struggling to accommodate the dengue patients and setting up additional beds on the corridors to provide treatment.

So far this year, approximately 2,000 patients visited the hospitals, with about 100 currently receiving treatment. The majority of these patients reside in Dhaka, specifically in areas such as Maniknagar, Basabo, Golapbagh, Dakshin Mugda, Mirpur, and Manda.

A similar scenario was seen at Dhaka Medical Hospital, Kurmitola General Hospital, Sir Salimullah Medical College, Mitford Hospital, DNCC Dedicated Covid-19 Hospital, and Suhrawardy Hospital, where dengue cases are increasing each day.

A. F. Hassan Ariff, adviser to the Ministry of Local Government, Rural Development and Cooperatives and the Ministry of Land, said instructions were given to all city corporations and municipalities to combat the spread of dengue by regularly monitoring and eliminating mosquito breeding grounds.

The adviser said, "Whenever dengue cases rise, we respond with various activities. However, if proactive measures are taken from the beginning and we raise awareness early on, we can significantly reduce dengue spread."

According to the local government department, efforts to prevent dengue nationwide have included the destruction of mosquito breeding grounds and the application of larvicide in 906 locations.

Inspections were carried out at 18,733 sites across the country, with 508 of those in City Corporation areas and 74 identified as vulnerable municipal areas, where action has been taken.

To combat the dengue outbreak this season, 2,689 mosquito control workers are actively engaged in all city corporations and at-risk municipalities.

In an emergency meeting, the local government department formed 10 teams to address the ongoing dengue situation. The program is being implemented and closely monitored in 12 City Corporations, including Dhaka South and North, as well as high-risk areas like Savar, Dohar, Tarab, and Rupganj.

DSCC Administrator Dr. Mohd Sher Ali said regular larviciding and adulticiding efforts are in place to control dengue by eliminating Aedes mosquito larvae and targeting adult mosquitoes. Besides, special mosquito control activities are conducted based on the reports of dengue patients admitted in various hospitals in the area, as provided by the Health Department, he said.

The DNCC administrator also said three monitoring teams from the local government department, along with 10 teams of DNCC officials, are conducting on-site inspections of larvicidal activities.

These inspections are carried out in two phases: the first from 7am to 10am and the second from 4pm to 6pm across the ten regions, he added.

Disease status

Dengue fever, spread by mosquitoes of the Aedes aegypti genus, is a serious illness causing symptoms like high fever, severe headaches, and joint pain. Some cases can progress to dengue haemorrhagic fever, which can be life-threatening, especially upon repeat infection with different virus types (serotypes) such as DENV-1, DENV-2, DENV-3, and DENV-4.

A recent icddr,b (International Centre for Diarrhoeal Disease Research, Bangladesh) study published in the American Journal of Tropical Medicine and Hygiene indicates that the outbreak in 2023 could have been primarily driven by the resurgence of the DENV-2 strain, responsible for about 74% of cases. Tests on blood samples from dengue patients confirmed DENV-2 as the predominant strain, followed by DENV-1 (20%) and DENV-3 (6%). Notably, DENV-1 was found to be more prevalent in rural areas like Cox's Bazar.

Several factors exacerbated the outbreak, including high urban population density, climate change impacts more specifically intermittent rainfall, rapid urbanisation without adequate planning, insufficient mosquito control measures, and increased travel.

Bangladesh reported a staggering 321,179 hospitalised dengue cases in 2023-significantly higher than previous years, causing widespread concern. The actual number of cases could be much higher.

Historically, different dengue strains have caused outbreaks at different times. From 2000 to 2002, DENV-3 led to numerous hospitalisations, while DENV-2 dominated from 2013 to 2018, followed by a resurgence of DENV-3 from 2019 to 2022. In 2023, DENV-2 once again caused the highest number of cases and fatalities.

Discussing the implications of the findings, Dr Mohammad Shafiul Alam, Scientist in the Programme for Enteric Infections and Vaccines, Infectious Diseases Division at icddr,b and Senior Author of the article, indicated that historical data shows when a particular dengue strain emerges or re-emerges, it tends to remain dominant for the next few years. Reinfection with the same strain is less likely. The resurgence of DENV-2 in 2023 suggests that the prevalence of dengue in Dhaka, where most of the cases were reported, may decrease in the coming years - something that may have contributed to the relatively fewer cases this year (although we must remain vigilant). Reinfection with a different serotype can be severe, making individual-level prevention and Aedes aegypti mosquito control critical priorities.

The study, conducted between July and December 2023, analysed 354 blood samples collected from patients aged between 5 and 65 years with clinical symptoms of dengue (e.g., onset of fever between 2 and 5 days and/or other symptoms, such as rash, myalgia, bone pain, headache, nausea, vomiting, and diarrhoea). These samples were collected from Alikadam (Bandarban), Shyamnagar (Shatkhira), Ramu, Teknaf, and Ukhiya (Cox's Bazar), representing rural areas, and from the districts of Dhaka, Chattogram, Rajshahi, and Cox's Bazar, representing urban areas.

This shift in predominant dengue strains underscores the critical need for effective mosquito control strategies and the development of a universal dengue vaccine capable of combating all serotypes.

No approved dengue vaccine is currently available, confining Bangladesh to environmental measures to curb the threat. "To prevent the disease, the government takes a number of measures, including building awareness about Aedes mosquitoes, conducting Aedes surveys and conducting anti-mosquito drives by local government units," said Dr Shyamol Kumer Das, Deputy Program Manager (Malaria and Aedes Transmitted Diseases) at the DGHS.

Faced with the recent surges, sources at DGHS said the health authority is devising a national action plan to control dengue virus transmission. That hasn't materialised yet. Last year, investigators from icddr,b and the Larner College of Medicine at the University of Vermont (UVM), USA, announced that they had conducted a successful phase 2 trial of a promising tetravalent single-dose dengue vaccine, TV005, in Bangladesh.

Beginning in 2016, the trial evaluated the safety, immunogenicity and durability of TV005 in 200 volunteers, who spanned a variety of ages. The vaccine was found to be "well tolerated and immunogenic for all four serotypes in young children to adults, including individuals with no previous dengue exposure," the researchers wrote in a Lancet Infectious Diseases paper.

Mohammad Moniruzzaman from Dhaka's Mirpur area was one of those volunteers. "I took the vaccine from the icddr,b in 2016, but I'm not infected with the viral disease yet while many of my family members and neighbours were infected with the disease," he told VaccinesWork. "There was no notable reaction of the vaccine as side-effects."

A senior scientist at icddr,b said that the institute is working on a phase 2B trial, among children aged between 1 and 17 years. Phase 3 trials will take place in India.

"We hope, if our phase 2B trial of the vaccine is successful and effective, then the vaccine can be used here. By using this vaccine, people of the country from children to adults can be prevented from the deadly viral disease," said the scientist, speaking on condition of anonymity since he isn't authorised to speak to the media.

If all goes well, it may still be another 3-5 years before the vaccine hits the market. Till then, existing prevention methods will need to be strengthened. The Aedes mosquito, vector of the dengue disease, will have to be controlled by community mobilisation. Cleanliness campaigns will have to be ensured all over the country round the year. Because the menace is well and truly alive.

Additional reporting by Masudul Hoque