Climate change and extreme weather will have complex effects on disease transmission

Climate change and extreme weather will have complex effects on disease transmission
The three temperature regimes used in our experiment. Our experimental design comprised seven constant temperature regimes with temperatures ranging from 10°C to 28°C, five variable temperature regimes mimicking diurnal temperature fluctuations of ±3°C around the mean, and four heatwave regimes where temperatures were identical to the equivalent constant treatment except during a 3-day period between days 20 and 23 when temperatures were raised by 6°C. All temperature treatments were exposed to the Daphnia parasite Ordospora and to a placebo infection that served as a control for parasite exposure. Constant temperature regimes were replicated 12 times (7×12×2=168 individuals), while in the variable temperature regimes, the number of replicates was increased to 18 as we expected increased mortality in these treatments (5×18×2=180 and 4×18×2=144, respectively, for the fluctuating and heatwave regime). All animals were terminated after day 27 and fitness estimates were collected within 3 days. Credit: DOI: 10.7554/eLife.72861

Temperature fluctuations such as heatwaves can have very different effects on infection rates and disease outcomes depending on the average background temperature, says a report published today in the journal eLife.

The study suggests it will be increasingly difficult to predict the consequences of on host-pathogen interactions as rise and become more common.

Infectious diseases have profound ecological effects on human, agricultural and wildlife populations. It is well known that interactions between pathogens and their hosts are sensitive to changes in temperature.

But what is less well understood is how sudden and extreme temperature variation affects this relationship and how this influences overall infection rates and disease outcomes.

"Climate change is predicted to increase not only but also and the frequency and intensity of extreme weather events," explains co-first author Pepijn Luijckx, William C Campbell Professor in Parasite Biology at Trinity.

"Yet although studies have quantified the effects of rising average temperatures on host and pathogen traits, the influence of variable temperature regimes such as heatwaves remains largely unknown."

Luijckx and the team examined the effects of different temperatures on various traits in a —a small crustacean called Daphnia magna—and its known gut parasite, Odospora colligata. Transmission of the parasite is representative of classic environmental transmission, similar to that seen with diseases such as COVID-19 and cholera.

The team looked at how the organisms responded to three distinct temperature regimes: a constant temperature, and two variable regimes, with daily fluctuations of +/- 3 degrees Celsius and three-day heatwaves of 6 degrees Celsius above ambient temperature. They then measured the crustacean's lifespan, fertility, infection status and the number of parasite spores within their gut. Next, they processed the data into a statistical model to compare the impact of the three different temperature regimes.

The team found that daily fluctuations of temperature reduced the infectivity and spore burden of the parasite compared to those kept at the constant average temperature. However, by contrast, the infectivity of after a heatwave was almost the same as the infectivity of those maintained at the constant temperature.

Moreover, the number of spores in the crustacean host increased following the three-day 'heatwave' when the background constant temperature was 16 degrees Celsius, but this burden was reduced at higher temperatures. This suggests that the effects of temperature variation differ depending on the average background temperature and whether this is close to the optimum temperature for the parasite.

Host fitness and reproductive success were generally reduced in the crustacean exposed to either the parasite spores or when experiencing variable temperatures. The difference between the host and pathogen responses suggest that under some circumstances the parasites were able to withstand the sudden change in heat better than their hosts.

"Our findings show that temperature variation alters the outcome of host-pathogen interactions in complex ways. Not only does temperature variation affect different host and pathogen traits in a distinct way, but the type of variation and the average to which it is applied also matter," concludes Professor Luijckx.

"This means that changing patterns of climate variation, superimposed on shifts in mean temperatures due to global warming, may have profound and unanticipated effects on disease dynamics."

More information: Charlotte Kunze, Pepijn Luijckx , Andrew L Jackson, and Ian Donohue, Alternate patterns of temperature variation bring about very different disease outcomes at different mean temperatures, eLife (2022). DOI: 10.7554/eLife.72861

Journal information: eLife

Citation: Climate change and extreme weather will have complex effects on disease transmission (2022, February 15) retrieved 1 June 2023 from
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