Bangladesh's deadliest dengue outbreak in 2023: DENV-2 to blame?

Dhaka, Bangladesh, 10 July 2024 - Dengue fever, spread by mosquitoes, 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.

In 2023, Bangladesh faced its most severe dengue outbreak in two decades, resulting in 1,705 deaths—making it the deadliest globally that year. A recent icddr,b study published in the American Journal of Tropical Medicine and Hygiene indicates that the outbreak could be 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 is 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; however, we must remain vigilant. However, 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.