A feeding female Anopheles arabiensis mosquito
A global review of studies looks at how climate affects zoonotic diseases - infections that spread from animals to humans such as COVID-19, the bubonic plague and the Ebola virus.
· The impact of climate change has only been scientifically investigated in around 6% of the 816 zoonotic diseases that affect humans.
· The findings highlight the risk posed by vector transmitted zoonotic diseases, spread by the likes of mosquitoes, ticks and fleas, as they are particularly sensitive to temperature, rainfall and humidity.
As the planet edges towards 1.5°C of global warming, a new study led by the Natural History Museum, London has revealed that scientists still have only a limited understanding of how climate change is reshaping the risk of infectious diseases that pass from animals to humans.
The research shows that a warmer world will alter weather patterns, transform habitats and shift where many animals live, likely bringing people and wildlife into closer proximity and increasing opportunities for zoonotic diseases to “spill over.” However, the exact impacts are extremely hard to predict.
By reviewing hundreds of scientific studies, the team were able to extract detailed climate-disease data for 53 zoonotic diseases - around 6% of the 816 known zoonotic diseases that affect humans. Even for these relatively well-studied diseases, responses to climate change are highly variable.
Overall, zoonotic diseases were found to be sensitive to climate, with temperature showing the clearest links. Higher temperatures were almost twice as likely to increase disease risk as to decrease it, particularly for zoonotic infections spread by mosquitoes. But this pattern was far from universal, and for other climate factors, such as rainfall and humidity, the picture was even more mixed.
The study found that zoonotic diseases are generally climate-sensitive but respond in a variety of ways depending on the disease, the animal host and the local environment.
Temperature showed the strongest and most consistent links. In many cases, warming increases risk for instance, by speeding up the development of mosquitoes or boosting rodent populations. However, even for a single disease, the response to temperature may change depending on how warm it already is, or which species are involved.
Co-author Dr David Redding uses plague as an example of this complexity:
“Plague is caused by a bacterium that circulates between rodents and the fleas that feed on them. Temperature strongly influences this system. Warmer conditions can boost rodent populations in some regions and speed up flea development, which can increase opportunities for transmission.
However, this relationship is not linear. At higher temperatures, the bacterium becomes less efficiently transmitted by fleas because the conditions that allow the flea to become infectious break down. Beyond a certain point, further warming reduces plague spread.”
The authors warn that inconsistent research approaches across disciplines and regions are obscuring the true relationships between climate and disease, making it difficult to compare results across studies or to provide clear guidance for public health.
Lead researcher Artur Trebski said there is an urgent need to rethink how climate-disease relationships are studied and reported.
“It’s sometimes suggested that climate change will make animal-borne diseases worse for humans in general, but our research shows that it’s much more complex than that,” says Artur. “We see so much variation, even within the same disease, so we need much more nuance in how we summarise the future health impacts of climate change.”
Dr Redding, who leads research into biodiversity and health at the Museum added that public health research needs to move away from a one-size-fits-all mindset.
“Climate change is an all-encompassing process that will affect nearly every single living thing on the planet,” says David. “The fact that there’s not a consistent way to examine how different animals and the diseases they carry are affected by this process is really surprising.”
“I hope that this study will be the start of moving people towards a common research framework that allows us to act in a more co-ordinated way. By better understanding the nuance of these relationships, we’ll be in a better place to design effective control measures,” he adds.
The findings are published in the journal Proceedings of the National Academy of Sciences (PNAS). DOI 10.1073/pnas.2422851122.
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