New research from scientists at Trinity College Dublin suggests that heatwaves have a big impact on how diseases spread. They found that many of our current ways of predicting disease might be missing some key information about heatwaves.
What did they find?
The scientists discovered that the details of a heatwave – like how much hotter it is than usual, and how long it lasts – can change how much a disease spreads by a lot, sometimes even 13 times more! They saw this in their experiments using a common lab animal, the water flea.
Why is this important now?
The world is experiencing more and more extreme weather, including heatwaves, because of climate change. For example, temperatures recently reached almost 50°C (122°F) in Pakistan, while South Africa had a sudden cold spell near freezing. With heatwaves becoming more common and stronger, it's really important to understand how they affect disease spread.
While scientists know some things about how regular temperatures affect viruses and germs, they know much less about the effects of sudden heatwaves or cold snaps, or how long these events last. This new study aimed to fill that gap.
How did they do the research?
Niamh McCartan, a student researcher at Trinity, explained that they used tiny water fleas (called Daphnia magna) and a specific germ (Ordospora colligata) that causes disease. This pair is often used to study diseases that spread through the environment.
Above: Parasite spore clusters (Ordospora colligata) look like black dots within the gut of the host (Daphnia magna). Credit: Niamh McCartan, Trinity College Dublin
They created 64 different "heatwave" scenarios. They changed:
- How hot the heatwave was (how much hotter than normal).
- How long the heatwave lasted.
- The average temperature the fleas were living in.
- When the fleas were exposed to the germ.
What were the main results?
The results showed that how hot a heatwave is, how long it lasts, and the normal temperature all work together in complex ways. This affects how much the germ spreads and grows.
Crucially, heatwaves were different from other temperature changes (like cold snaps). They could increase the number of germs by up to 13 times, leading to very different infection outcomes.
What does this mean for us?
Niamh McCartan pointed out that a recent study found climate change has made 58% of human diseases worse. Temperature changes can affect our immune systems and even our behaviour, making us more or less likely to get sick.
This new research highlights that we need better, more detailed models to predict how heatwaves and climate change will affect different diseases. Simple models that only look at average temperatures might miss important details.
For example, some researchers believe that if there hadn't been heatwaves in the summer of 2022, nearly 70% of COVID-19 cases could have been avoided. Imagine how understanding heatwaves better could have helped so many people!
Climate change is also causing mosquitoes that carry diseases like dengue, Zika, and malaria to appear in places like Italy and France, where it used to be too cold for them. While Ireland hasn't been as affected yet, this study emphasizes the urgent need to understand how warming and extreme weather can change disease patterns more broadly.
In short: Future disease predictions need to consider sudden and extreme temperatures, not just average ones.
Beyond human health:
These findings also have important implications for freshwater environments. Water fleas are a key food source for many other species. If their numbers drop due to disease, it can disrupt the entire food web. Also, if there are fewer water fleas, algae can grow out of control, harming water quality.
This research was supported by funding from Research Ireland. You can read the full scientific article on the PLOS Climate website.