Climate change responsible for severe infectious disease in UK frogs

Common frog Rana temporaria 4 (c) Greg Hitchcock

Climate change has already increased the spread and severity of a fatal disease that infects common frogs (Rana temporaria) in the UK, according to research involving the University of Plymouth.

Historic trends in mass-mortality events attributed to the disease (similar to Ebola in humans), caused by the Ranavirus, were found to match the pattern of increased temperatures recorded over recent decades.

Disease outbreaks are also predicted to become more severe, more widespread and occurring over a greater proportion of the year within the next few decades if carbon emissions continue at their current rate.

The research was led by international conservation charity ZSL (Zoological Society of London), UCL and Queen Mary University of London, working with Dr Robert Puschendorf, Lecturer in Conservation Biology at the University of Plymouth.

It used a three-pronged approach involving cell cultures, live models and historic data from the Met Office and Froglife’s Frog Mortality Project, with the research demonstrating that warm weather – where temperatures reach 16°C – dramatically increases the risk of Ranavirus causing a disease outbreak in common frogs.

The findings, published in Global Change Biology, help explain the seasonality of the disease, with incidence peaking during the hottest months of the summer, showing that climate change could see outbreaks becoming more frequent from April to October.

Disease outbreaks in the spring could result in the deaths of large numbers of tadpoles, which could have repercussions for population survival.

Up to now, Ranavirus disease has been largely restricted to England. But as average monthly temperatures increase to exceed 16°C in more areas over longer periods, as predicted by the Intergovernmental Panel on Climate Change’s high carbon-emission model, the disease is likely to spread across most of the UK in the next 50 years.

Images of the common frog courtesy of Desmond Loughery; Nicola Devine; ZSL

<p>Common Frog (c) Londonderry Desmond Loughery #2<br></p>
<p>Froglet TGs 14th August 2018 (c) Nicola Devine<br></p>
<p>Image of wildlife pond with shade and vegetation for frogs courtesy of Paul Kleiman's garden (c) ZSL<br></p>

Dr Stephen Price, lead author from ZSL’s Institute of Zoology and UCL, said:

“Climate change isn’t something that’s just happening in faraway places – it’s something real and present that’s already had hard-to-predict impacts on wildlife in our own back gardens here in the UK. A number of scientists have already alluded to the fact that climate change could increase the spread of disease, but this is one of the first studies that provides strong evidence of the impact of climate change on wildlife disease, and helps to explain how it may facilitate the spread of Ranavirus across the UK.”

Dr Puschendorf added:

"This is yet another example of a lethal disease having an increased impact on natural systems due to a changing climate. There are no silver bullets left to sort this out at a global scale other than the obvious – appreciate the negative impact they are having and stop relying on fossil fuels as we go about our daily lives.”

ZSL scientists suggest that frogs may be better able to cope with infection if they have areas in which they can cool down – adding log piles, vegetation or nearby shady patches as well as keeping ponds deep will help reduce the level of sun exposure frogs receive, and thus reduce the growth rate of the virus.

Professor Trenton Garner, at ZSL’s Institute of Zoology, said:

“Many studies in amphibian disease cannot do much beyond saying ‘we have a problem’. This research offers a number of options for mitigation; however, this is only a short-term solution of course – if we don’t eventually slow and reverse human-driven climate change, we unfortunately can only expect things to get worse for our amphibians.”