Brazil warns dengue cases could hit 5mn as extreme weather takes toll

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Health officials in Brazil have warned that the number of dengue cases in the country could hit a record 5mn this year as climate change and the El Niño weather pattern in the Pacific Ocean fuel the spread of mosquito-borne diseases.

“We have a situation that is very worrying because of climate change [and] mainly the El Niño phenomenon,” said Ethel Maciel, secretary of surveillance at the health ministry. “There will be [an acceleration] in transmission.”

The ministry’s worst-case scenario of 5mn cases would represent more than a three-fold increase from the caseload of 1.6mn recorded in 2023 that resulted in 1,079 deaths. Its average projection is for 3mn cases this year.

El Niño, a naturally occurring warming of sea surface temperatures in the Pacific Ocean, is believed by many scientists to be driving increasingly severe weather patterns worldwide. Some meteorologists say its effects are being exacerbated by climate change.

In Brazil, the current El Niño pattern has been linked to a record heatwave, extreme drought in the Amazon rainforest and prolonged heavy rains and flooding in the country’s south.

These conditions have enabled increased transmission of mosquito-borne viruses such as dengue, chikungunya and zika, which was linked to a surge in microcephaly cases — babies born with a very small head — in Brazil in 2015-16.

“The mosquito depends on heat, it grows more with heat and rain. So as long as the temperature is kept higher for a long time, the replication of the mosquito and, consequently, the virus is facilitated,” said Ester Sabino, professor at the Institute of Tropical Medicine at São Paulo university.

“We’re having higher temperatures for longer and this means that transmission occurs for a longer period of time during the year. We will probably see an increase in chikungunya cases, too.”

A potentially fatal disease, dengue can cause high fever, muscle pain and internal bleeding. It is transmitted by the Aedes aegypti mosquito, which thrives in pools of stagnant water. Chikungunya is spread by the same mosquito type and provokes similar symptoms to dengue but is caused by a different virus.

The number of reported dengue cases in Brazil rose 16 per cent in 2023 compared with the previous year. This year, the health ministry has warned of an “epidemic level” of cases in Brazil’s central-west region as well as a “potential epidemic” in the south-east.

The virus has four serotypes — or variations — and infection by one does not create immunity for the others. Brazilian health officials are particularly concerned this year because of the re-emergence of the third serotype known as DENV-3.

“For the first time in a long time we have four serotypes circulating in Brazil,” said Maciel. “Serotype three had not been present since 2007, so we will have many susceptible people.”

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

The health body reported more than 5mn dengue cases worldwide last year. It said Brazil accounted for more than 2.9mn of the global total, according to its own data for suspected cases.

Sabino said the country’s overweighting in the number of suspected cases was probably due to Brazil’s stricter standards of notification.

The health ministry last month rolled out a dengue vaccine, but supply has been restricted to priority regions due to manufacturing bottlenecks.

Additional reporting by Beatriz Langella