Cold snaps lead to a 5-fold increase or a 3-fold decrease in disease proliferation depending on the baseline temperature.

Background: Climate change is driving increased extreme weather events that can impact ecology by moderating host-pathogen interactions. To date, few studies have explored how cold snaps affect disease prevalence and proliferation. Using the Daphnia magna-Ordospora colligata host-parasite system, a popular model system for environmentally transmitted diseases, the amplitude and duration of cold snaps were manipulated at four baseline temperatures, 10 days post-exposure, with O. colligata fitness recorded at the individual level.

Results: Cold snaps induced a fivefold increase or a threefold decrease in parasite burden relative to baseline temperature, with complex nuances and varied outcomes resulting from different treatment combinations. Both amplitude and duration can interact with the baseline temperature highlighting the complexity and baseline dependence of cold snaps. Furthermore, parasite fitness, i.e., infection prevalence and burden, were simultaneously altered in opposite directions in the same cold snap treatment.

Conclusions: We found that cold snaps can yield complicated outcomes that are unique from other types of temperature variation (for example, heatwaves). These results underpin the challenges and complexity in understanding and predicting how climate and extreme weather may alter disease under global change.