Climate change fuels most infectious diseases, new study finds

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 growing impacts of induced climate change by greenhouse gases.

That’s the sobering conclusion of a new paper, the first of its kind, which combed through more than 70,000 scientific studies to determine how a range of climate risks impacted 375 disease-causing diseases known to have affected humans. A team of 11 researchers from the University of Hawaii at Manoa conducted the analysis, which has been published Monday in the peer-reviewed scientific journal Nature Climate Change.

“I have to tell you, when this database started growing, I started getting scared, man,” Camilo Mora, UH Manoa climatologist and lead author of the paper, told HuffPost. “We have just started to realize that this one thing we do – emitting greenhouse gases – can influence 58% of all diseases that have affected humanity. You realize the extent of the vulnerability in which we are. I went from excited to terrified.

Scientists have long known and warned that climate breakdown fuels infectious diseases, making them more frequent and dangerous. But the new paper quantifies the extent of this growing threat, finding that 58% of all documented infectious diseases – 218 out of a total of 375 – have been aggravated in some way by one or more associated climate hazards. to greenhouse gas emissions, including warming temperatures, drought, wildfires, sea level rise and extreme rainfall.

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

The research team dug into the existing scientific literature on a myriad of pathogens – viral, bacterial, fungal, animal-based and more – and found that warming temperatures negatively impact 160 unique diseases , the highest of all climate impacts 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 other hand, the analysis identified 63 diseases that were diminished in some way by climatic hazards; however, 54 of them were also aggravated by one or more other climate impacts.

The study comes as the world continues to grapple with an evolving COVID-19 pandemic that has so far killed 6.4 million people worldwide and infected more than half a billion, according to Data of the World Health Organization. And as the new paper points out, there is evidence that climate impacts, particularly changes in rainfall and temperature, have had mixed effects on disease transmission.

A 2020 study “suggested that heavy rains could exogenously induce social isolation, helping to explain the drop in COVID-19 cases after heavy rains; however, increased COVID-19 cases have been associated with increased rainfall in Indonesia, possibly reflecting different behavioral responses to extreme rainfall,” the paper states, summarizing the available research. “Higher temperatures have been associated with an increase in COVID-19 cases in some cases, and although no mechanism has been described, it is possible that extreme heat is forcing people indoors, which may increase the risk of virus transmission, especially when combined with poor or reduced ventilation.”

Volunteers wearing personal protective equipment spray disinfectant at an exam site ahead of the Chinese National University Entrance Examination on June 5, 2022 in Bozhou, China's Anhui province.  (Photo by Zhang Yanlin/VCG via Getty Images)
Volunteers wearing personal protective equipment spray disinfectant at an exam site ahead of the Chinese National University Entrance Examination on June 5, 2022 in Bozhou, China’s Anhui province. (Photo by Zhang Yanlin/VCG via Getty Images)

In their paper, the UH researchers break down the ways one crisis helped fuel another. Climate change has brought people and pathogens closer together. Warming temperatures and changes in rainfall have allowed mosquitoes, ticks, birds and other disease vectors to expand their ranges, while human movement and migration due to rising sea ​​level and extreme weather conditions led to new contacts with dangerous pathogens, the analysis notes. Warmer land temperatures lead to an increase in mosquito-borne viruses like dengue fever, while warming oceans have been linked to significant increases in vibriosis, bacterial infections caused by eating contaminated seafood or swimming in contaminated water. Additionally, climate impacts have allowed pathogens to reproduce more successfully and become more virulent, while simultaneously blunting our own ability to avoid and fight disease.

Many infectious diseases have been negatively influenced by multiple climatic hazards. For example, leptospirosis, a bacterial disease transmitted through contact with the urine of infected animals, was aggravated by eight distinct climate impacts, including warming, flooding, extreme rainfall and even drought, according to the results.

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

Mora said the dynamic presents monumental challenges.

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

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

NurPhoto via Getty Images

A particularly alarming example of how warming can unleash disease occurred in 2016, when anthrax, a rare bacterial disease, exploded in a remote Siberian village. A child died and dozens of people were hospitalized. The scientists finally assigned the outbreak to a summer heat wave that melted the permafrost and exposed the carcass of an infected 75-year-old reindeer, releasing spores of the bacteria that causes anthrax. Thousands of reindeer eventually died from the epidemic.

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

Luis Ostrosky, chief of infectious diseases at McGovern Medical School at UTHealth Houston, 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 shifts 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 the droppings of birds and bats. While historically only found 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 of its common range in the Southwest.

“It’s thought to be related to climate change and bird migration, both of which are deeply intertwined,” Ostrosky said of the changes.

Ostrosky was not involved in the UH study but applauded the authors for their comprehensive effort to quantify the clear changes scientists are observing around the world.

“If nothing else, this really brings the data together in a very elegant way and it indicates that indeed, with climate change, we are going to see dramatic changes in the patterns of infectious disease spread and human infection. .”

As for humanity’s adaptability, Ostrosky says we don’t have much choice.

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

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

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

“I started studying this thing and realized it was transmitted by mosquitoes, which people like no other the business of 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 couldn’t help thinking how affected I was myself.”

Along with the article, the UH Manoa team published a interactive tool which allows users to filter data by climatic hazards, types of transmission and individual diseases.

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