How climate change is giving the world’s worst diseases a deadly boost

The sprayers climb down from their pick-up, shoulder their metal pesticide tanks and fan out through the village. With their drab overalls, boots and backpacks, they vaguely resemble the characters from the film Ghostbusters.

House by house, they go into each room and methodically spray the walls with milky pesticide to kill any mosquitoes and the malaria they might carry.

Similar teams had already treated this area of Boane, an hour’s drive from Mozambique’s capital, Moputo. They should not normally need to return until September but they have been called back early due to an unusual resurgence of the disease.

Malaria’s normal seasonal cycle has been disrupted as a result of catastrophic flooding earlier in the year caused by Cyclone Freddy, the latest example of the extreme weather events predicted to become more common due to climate change.

Now should be the dry season with few mosquitoes, but there are pools of standing water everywhere attracting the insects.

“There are many mosquitoes now and many cases of malaria,” explains Neli Machoi, one of the sprayers. “The campaign had been finished, then we were called back because we were registering more cases of malaria than before.”

Cases of the mosquito-borne sickness have risen, and Mozambican health officials are worried the uptick will start to eat into decades of gains against the ancient disease.

But it’s not just experts in Mozambique who are concerned about a reversal in progress. Set against a backdrop of increasingly unpredictable and extreme weather events, other countries are starting to report an untimely rise in malaria infections.

As well as the example of Mozambique and Cyclone Freddy, the longest-lived tropical cyclone on record, last year’s unusually heavy monsoon in Pakistan saw malaria cases jump four-fold. Health experts are now waiting to see whether the powerful Cyclone Mocha, which hit Bangladesh and Myanmar last week, will also heighten the disease’s prevalence.

Experts predict that continuing changes and shifts in the globe’s weather patterns could heighten the threat posed by humanity’s most dangerous infectious diseases, making this the deadliest fallout of climate change, rather than extreme temperatures or flooding.

“At the moment, if you look at the climate change discussions, the world hasn’t really grappled with the health impact,” says Peter Sands, executive director of the Global Fund to fight AIDS, Tuberculosis and Malaria.

“Infectious disease is likely to be one of the single most, if not the single most powerful levers where climate change can translate into people being killed.”

For Flaminha Antonio, who was flooded out of her house in Boane by the cyclone in February, the link seems clear.

There are still large patches of standing water in the fields around the mother-of-three's home.

“Now there are many mosquitoes and if you look around, day and night, they are all over,” she explained while waiting for the sprayers to finish inside her home. Sprayers had already protected her house last September, but the floods washed all the insecticide residue away.

‘Malaria is a highly climate sensitive disease’

The waters reached her house in the early hours one February night with little warning. Residents said a decision to open dam gates nearby had added to the speed of the flooding.
In a matter of hours, the water was nearly waist deep in her home and did not recede for five days.

It was around two weeks later that she felt the ominous fever, chills and aches of malaria. Her newborn son also fell ill, but fortunately recovered. Flaminha’s neighbours have been struck down, too. “There are many cases,” she says.

Mozambique’s efforts against malaria, paid for by the Global Fund, have yielded good results in recent decades. At the start of the 21st century, cases in the south of the country used to reach around 600,000 every year. Today, this number stands at 50,000, according to Goodbye Malaria, which carries out spraying in the region.

Yet malaria’s transmission by mosquitoes means it is very directly affected by climate shifts, says Mr Sands. Climate change is already making it more difficult to tackle the infection, which killed 619,000 people in 2021 – the second highest figure in nearly a decade.

“Malaria is a highly climate sensitive disease and we are seeing this pretty dramatically demonstrated,” he said. “We also saw it in Pakistan and we've also seen it in Malawi and we are seeing it in different places.”

Studies have shown the geographical distribution of mosquitoes has broadened with changing climate. This means the insect is carrying the disease into more and more new countries.

A 2021 study published in the Lancet Planetary Health estimated that in a worst case scenario, if carbon emissions continued to increase at current levels, up to 8.4 billion people could be at risk from malaria and dengue, another mosquito-borne disease, by the end of the century.

Other deadly infections such as tuberculosis, a bacterial infection spread by coughs and sneezes, may also be more indirectly affected as a result of climate change. If droughts and crop failures force people from their homes into crowded camps, then TB might flourish.

“The way TB works, it likes nothing better than very large numbers of highly stressed people living in close proximity, so refugees and displaced people,” says Mr Sands.

He went on: “Of course the world has come out of Covid-19 thinking the next threat is a new pathogen, which it might be, but on the other hand the next health crisis may actually be the impact of climate change on existing pathogens.”