Climate change supercharges most infectious diseases, new study shows

A new paper has found that 58% of infectious diseases tracked by researchers were exacerbated in some way by climate change-related hazards.  (Photo: Illustration: Jianan Liu/HuffPost)

A new paper has found that 58% of infectious diseases tracked by researchers were exacerbated in some way by climate change-related hazards. (Photo: Illustration: Jianan Liu/HuffPost)

A new paper has found that 58% of infectious diseases tracked by researchers were exacerbated in some way by climate change-related hazards. (Photo: Illustration: Jianan Liu/HuffPost)

More than half of all human infectious diseases in recorded history – Lyme, West Nile, hantavirus, typhoid, HIV and influenza, to name a few – have been exacerbated by the increasing effects of greenhouse gas-driven climate change.

That’s the sobering conclusion of a new, first-of-its-kind study that combed through more than 70,000 scientific studies to find out how a range of climate hazards have affected 375 pathogenic diseases known to have affected humans. A team of 11 researchers at the University of Hawaii at Manoa conducted the analysis, which was published Monday in the peer-reviewed scientific journal Nature Climate Change.

“I have to tell you, as this database started to grow, I started to get scared, man,” Camilo Mora, a climate scientist at UH Manoa and the paper’s lead author, told HuffPost. “We were just beginning to realize that this one thing we’re doing – greenhouse gas emissions – could be affecting 58% of all the diseases that have affected humanity. You realize the extent of the vulnerability we’re under. I went from excited to terrified.”

Scientists have long known and warned that climate breakdown supercharges infectious diseases, making them more frequent and dangerous. But the new paper quantifies the scale of the growing threat, concluding that an impressive 58% of all documented infectious diseases – 218 of the 375 total – have been exacerbated in some way by one or more climate hazards associated with greenhouse gas emissions, including warming temperatures , drought, forest fires, sea level rise and extreme rainfall.

Mora stressed that this estimate, as alarming as it is, is conservative. The findings draw exclusively on cases with evidence linking climate hazards to infectious diseases, he said.

The research team dug through the existing scientific literature on myriad pathogens—viral, bacterial, fungal, animal-borne and more—and found that warming temperatures adversely affected 160 unique diseases, the highest of any climate impact analyzed. Extreme rainfall affected 122 diseases, followed by floods (121), drought (81), storms (71), land cover change (61), ocean climate change (43), fires (21), heat waves (20) and sea level rise (10) .

On the flip side, the analysis identified 63 diseases that were somehow reduced by climate hazards; However, 54 of these were also worsened by one or more other climate impacts.

The study comes as the world remains in the grip of an ever-evolving COVID-19 pandemic that has so far killed 6.4 million people globally and infected more than half a billion, according to World Health Organization data. And as the new paper highlights, there is evidence that climate impacts, particularly changes in rainfall and temperatures, have had mixed effects on the transmission of the disease.

A 2020 study “suggested that heavy rainfall could exogenously induce social isolation, helping to explain lower cases of COVID-19 following heavy rainfall; however, increased cases of COVID-19 were associated with increases in rainfall in Indonesia, perhaps reflecting different behavioral responses to extreme rain,” the paper said, summarizing the available research. “Higher temperatures have been associated with increased cases of COVID-19 in some cases, and although a mechanism was not outlined, it is possible that extreme heat forces people indoors, which can increase the risk of virus transmission, especially when combined with poor or reduced ventilation.”

Volunteers wearing personal protective equipment spray disinfectant at an examination site ahead of China's national college entrance examination on June 5, 2022 in Bozhou, Anhui province of China.  (Photo by Zhang Yanlin/VCG via Getty Images) (Photo: VCG via Getty Images)

Volunteers wearing personal protective equipment spray disinfectant at an examination site ahead of China’s national college entrance examination on June 5, 2022 in Bozhou, Anhui province of China. (Photo by Zhang Yanlin/VCG via Getty Images) (Photo: VCG via Getty Images)

Volunteers wearing personal protective equipment spray disinfectant at an examination site ahead of China’s national college entrance examination on June 5, 2022 in Bozhou, Anhui province of China. (Photo by Zhang Yanlin/VCG via Getty Images) (Photo: VCG via Getty Images)

In their paper, UH researchers break down the ways in which one crisis has helped fuel another. Climate change has brought humans and pathogens closer together. Warming temperatures and precipitation changes have allowed mosquitoes, ticks, birds and other disease vectors to expand their range, while human displacement and migration from sea-level rise and extreme weather have resulted in new contacts with dangerous pathogens, the analysis notes. Warmer land temperatures are driving an increase in mosquito-borne viruses such as dengue fever, while warming oceans have been linked to large increases in vibriosis, bacterial infections caused by eating contaminated seafood or swimming in tainted water. In addition, climate impacts have enabled pathogens to reproduce more successfully and become more virulent, while blunting our own ability to avoid and fight disease.

Many infectious diseases have been negatively affected by several climate hazards. For example, leptospirosis, a bacterial disease transmitted through contact with the urine of infected animals, has been exacerbated by eight separate climate impacts, including warming, floods, extreme rainfall and even drought, according to the findings.

But the problem is far more complex than how a single climate stressor can interact with and exacerbate each infectious disease. It is not a 1-to-1 connection; many pathogens can be transmitted to humans in several different ways. The article identified more than 1,000 unique pathways between climate hazards and disease outbreaks.

Mora said that dynamics present monumental challenges.

“It’s so naive for us to think we’re going to be able to adapt to this,” he said. “There’s no way, with so many diseases and so many different pathways, that we can fully adapt. To me, it made it very clear that if we really want to avoid this problem, the best way to avoid it is to deal with greenhouse gas emissions. The last thing we want to do is unleash the power of one of these diseases that can be affected by greenhouse gases.”

Dengue-infected patients treated in a special ward at a hospital in Dhaka, Bangladesh on June 13, 2022. (Photo: Kazi Salahuddin Razu/NurPhoto via Getty Images) (Photo: NurPhoto via Getty Images)

Dengue-infected patients treated in a special ward at a hospital in Dhaka, Bangladesh on June 13, 2022. (Photo: Kazi Salahuddin Razu/NurPhoto via Getty Images) (Photo: NurPhoto via Getty Images)

Dengue-infected patients treated in a special ward at a hospital in Dhaka, Bangladesh on June 13, 2022. (Photo: Kazi Salahuddin Razu/NurPhoto via Getty Images) (Photo: NurPhoto via Getty Images)

A particularly alarming example of how warming can unleash disease occurred in 2016, when anthrax, a rare bacterial disease, broke out in a remote village in Siberia. One child died and dozens of people were hospitalized. Researchers at last attributed the onset of a summer heat wave that thawed permafrost and exposed the carcass of a 75-year-old infected reindeer, releasing spores of the bacteria that cause anthrax. Thousands of reindeer eventually died from the outbreak.

“You can imagine how many diseases have accumulated over time in these ice caps, and now when they start to melt, all these diseases are starting to be exposed,” Mora said.

Luis Ostrosky, chief of infectious diseases at UTHealth Houston’s McGovern Medical School, now spends most of his time studying COVID-19 and monkeypox. But one of his specialties is mycology, the study of fungi. He jokes that it has now become his “night job”.

In recent years, mycologists have documented significant geographic changes to fungi that for centuries were only found in certain regions, he said. Histoplasmosis, for example, is an infection caused by inhaling the spores of a fungus found in bird and bat droppings. While historically found only in the eastern half of the United States, it is now beginning to appear in western states. Likewise, coccidioidomycosis, a fungal disease better known as “valley fever,” is increasingly appearing outside its usual range in the Southwest.

“This is believed to be related to climate change and bird migration, both deeply linked,” Ostrosky said of the changes.

Ostrosky was not involved in the UH study, but applauded the authors for their extensive efforts to quantify the clear changes scientists are observing across the globe.

“If nothing else, it really puts the data together very elegantly, and it points to the fact that indeed with climate change we’re going to see dramatic changes in the patterns that infectious diseases spread and infect people.”

When it comes to humanity’s ability to adapt, Ostrosky says we don’t have much choice.

“I think we are very resilient as a species. We have to adapt to a lot of things, one of them is pathogens,” said Ostrosky. “But it’s very worrying.

Mora has a personal connection to the study’s findings. He is from a rural area outside of Cali, Colombia. During a visit home several years ago, he was infected with chikungunya, a mosquito-borne virus that causes fever and severe joint pain. Planetary warming, extreme rainfall and flooding all contribute to outbreaks of the disease, the new analysis found.

Mora called his battle with chikungunya one of the most brutal, painful experiences of his life.

“I began to study this thing and I realized that it is transmitted by mosquitoes, which populate like nobody’s business with heat and excess rain – two things that are becoming so common in my country.” he said, speaking via Zoom from his family farm in Colombi. “I could not resist thinking to what extent even I myself was affected.”

Together with the newspaper, the team from UH Manoa published a interactive tool which allows users to filter the data by climate hazards, types of transmission and individual diseases.

Also on HuffPost

This article originally appeared on HuffPost and has been updated.

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