As dengue spreads to new areas around the world, it is becoming less predictable

Something unusual seems to be happening with dengue, a potentially fatal mosquito-borne viral disease found across swathes of tropical Africa, Asia and the Americas. As with most infectious diseases, the number of cases tends to rise and fall over the years as epidemics come and go, but recently changes seem to be afoot in how dengue is behaving.

Not only is the number of new infections steadily rising around the world, but outbreaks are becoming larger and less predictable. For example, 2019 saw the greatest number of dengue fever cases ever recorded – almost twice as high as the previous year. And in July 2023, there were a record number of deaths from the disease in Bangladesh.

Most people infected with dengue will suffer from flu-like symptoms, ranging from relatively mild to very unpleasant, with fever, headache and joint pain.

In more severe cases, though, blood vessels can become damaged by the virus, allowing blood to leak into the surrounding tissues. This condition, known as dengue haemorrhagic fever, can produce bruising, and bleeding from the nose and gums. It can ultimately lead to organ failure and death as the body slips into shock.

The principal agent, or vector, in the transmission of dengue, is the Asian Tiger mosquito Aedes aegypti, although its cousin Aedes albopictus is also capable of...

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