Brazil already exceeds worst-case forecast for dengue cases this year

Brazil has surpassed its worst-case forecast for dengue cases this year, registering a record 5.5mn infections as health officials and scientists warn that climate change will fuel the global spread of the mosquito-borne virus.

The surge is being driven by hotter weather and the El Niño warming phenomenon in the Pacific Ocean, which have affected the Latin America’s most populous nation for much of the past year, with health experts warning that higher global temperatures will make dengue epidemics more common.

In January, the health ministry warned the number of dengue cases could, in the most extreme scenario, reach 5mn this year. Its average projection was for 3mn cases. Multiple states have introduced emergency measures and vaccination programmes.

The 5.5mn cases registered by this week mark a 240 per cent jump from the 1.6mn recorded in 2023. Last year’s total was already one of the highest levels on record.

To date this year Brazilian health authorities have reported 3,200 confirmed deaths from dengue, which can cause high fever, muscle pain and internal bleeding. A further 2,700 deaths are being investigated. Brazil’s Federal District, which includes the national capital Brasília, has the highest rate of infections.

The dengue virus is transmitted by the Aedes aegypti mosquito, which thrives in pools of stagnant water. Chikungunya, another mosquito-borne disease which is present in Brazil, provokes similar symptoms to dengue but is caused by a different virus.

The World Health Organization has described dengue as a “substantial public health challenge”, noting a “10-fold surge” in worldwide reported cases from 500,000 a year to 5.2mn between 2000 and 2019.

Scientists and medical experts say the surge in cases is being fuelled by higher temperatures linked to climate change and that countries around the world can expect dengue outbreaks in the future. Late last year the WHO warned that there had been reports of indigenous cases in many southern European countries.

“We used to have five days of anomalous heat [during the summer]. Now there are 20 or 30 days,” said Christovam Barcellos, a researcher at the Oswaldo Cruz Foundation, referring to Brazil’s central regions.

“This triggers the dengue transmission process, both because of the [spread of the] mosquito and because of the movement of people.”

Felipe Naveca, another researcher at the foundation, said the increase in temperature aided the rapid maturation of virus-carrying mosquitoes, while shifts in rainfall patterns caused by climate change could increase the availability of breeding sites.

The dengue virus has four serotypes — or variations — and infection by one does not create immunity from the others. Health officials have said the current predominant serotype is type 2, against which the Brazilian population is less immunised.

Following the surge in cases in the first five months of this year — Brazil’s summer runs from late December to late March — the epidemic has shown signs of slowing down as temperatures cool.

At a press conference this month, Ethel Maciel, the health surveillance secretary at the health ministry, said the growth in cases was no longer “expressive [but] we still need to remain on alert”.

Maciel added that she expected case numbers to begin to rise again at the end of the year.

Additional reporting by Beatriz Langella