New method to predict impact of global warming on diseases

Scientists have devised a method for predicting how rising global temperatures are likely to affect the severity of diseases mediated by parasites.

The method, published in the journal PLOS Biology, can be applied widely to different host-pathogen combinations and warming scenarios.

It should help to identify which infectious diseases will have worsened or diminished effects with rising temperatures, said researchers from Trinity College Dublin in Ireland.

The method, which was road-tested using the water flea (Daphnia magna) and its pathogen (Ordospora colligata) as a model system, uses a long-standing biological concept known as the metabolic theory of ecology to predict how a wide range of processes - all of which influence host-parasite dynamics - are affected by temperature.

"Rising temperatures due to global warming can alter the proliferation and severity of infectious diseases, and this has broad implications for conservation and food security," said Pepijn Luijckx, a professor at the University of Toronto in Canada.

"It is therefore really important that we understand and identify the diseases that will become more harmful with rising temperatures, with a view to mitigating their impacts," Luijckx said.

This has always been very difficult - because temperature affects many processes in the host and the pathogen in different ways, it is hard to predict the cumulative effect that a rise (or drop) in temperature will have, researchers, said.

For example, while host immune function and pathogen infectivity may be higher as temperatures rise, pathogen longevity may be lower, they said.

Additionally, to predict the severity of disease, data is needed that does not always exist on the temperature sensitivity of all the processes involved, especially for newly emergent diseases.

The metabolic theory of ecology can be used to predict how various biological processes respond to temperature.

It is based on the idea that each process is controlled by enzymes, and that the activity and temperature dependence of these enzymes can be described using simple equations.

Even with limited data, the theory thus allows for the prediction of the temperature dependence of host and pathogen processes.

"By using the metabolic theory of ecology we can estimate the thermal dependence of each individual process, step by step, and calculate a final prediction of disease severity at different, changing temperatures," Luijckx said.

"Until now, no study has shown if this works for simple - unicellular - pathogens growing within their host, but we have been able to show that the method works very well in the model system we used," he said.