Why dengue is getting deadlier — even when we know the rules

Every year, as soon as the season changes towards monsoon, along with rising humidity, Bangladesh readies itself for a familiar battle. We know the drill by now — empty water containers, wear long sleeves, use mosquito nets, dab mosquito repellent, and call for fogging when needed. Yet despite all the precautions, dengue continues to rise, and more alarmingly, so does the death rate.

The question that now looms over every hospital ward and worried household is simple: why are we losing the fight even when we know what to do? According to Dr Syed Abu Sayeed, Emergency Medical Officer at Cox's Bazar Sadar Hospital, the problem lies in the fact that both the mosquito and the virus are changing faster than we can keep up.

"There are many variations of the female Aedes mosquito now. Vector change is leading to a rise in the rate of infection," he explains. What this means is that the mosquitoes spreading dengue — mainly Aedes aegypti and Aedes albopictus — are evolving, breeding in new environments, and becoming more resistant to control measures.

At the same time, the dengue virus itself has grown more complicated. There is not just one type of dengue — there are four, known as DENV-1 through DENV-4. Bangladesh used to see one or two dominate a season, but now, all four are circulating at once.

This creates a dangerous overlap.

"When someone gets dengue twice or more, the antibody of the first type can conflict with the second, creating a deadly reaction," says Dr Sayeed.

This is the reason behind the higher fatality rate — a phenomenon known in medical terms as cross-infection or antibody conflict. In simple words, your body's own defence system can overreact the second time, leading to severe complications such as shock, internal bleeding, or organ failure.

To make matters more complex, there is still no widely available dengue vaccine. While some candidates are in clinical trials, there is not yet one that can safely protect everyone against all four types of the virus.

Scientists face a delicate balance — they need a vaccine that works for people who have never had dengue before, as well as those who already have some immunity. Until that breakthrough comes, prevention and early detection remain our strongest weapons.

But science alone doesn't tell the full story. Our changing environment plays a role too. Humidity, unpredictable rainfall, and warmer temperatures now give mosquitoes more time and space to breed. Rapid urbanisation, clogged drains, and uneven waste management all make controlling the spread even harder.

And then there's human behaviour — the delays in seeking treatment, overcrowded hospitals, and limited awareness of warning signs like sudden abdominal pain or persistent vomiting. Many patients arrive at hospitals only when their condition turns critical, and by then, the chances of recovery sharply drop.

So, while the preventive advice remains the same, the battlefield has changed. The mosquitoes are adapting, the virus is mutating, and the climate is helping both.

What's needed now is a collective push — cleaner surroundings, faster medical response, and greater awareness that dengue isn't just a seasonal inconvenience anymore; it's a shifting, evolving threat.