Climate change has already increased the spread and severity of a fatal disease that infects common frogs in the UK, according to research led by Queen Mary University of London, Zoological Society of London (ZSL)’s Institute of Zoology and University College London (UCL).
Common frog Rana temporaria. Credit: Greg Hitchcock
The research, published in Global Change Biology, looked at a disease known as ranavirus, which can kill a large number of frogs in a short time.
Historic trends in mass-mortality events attributed to the disease were found to match the pattern of increased temperatures recorded over recent decades, with disease outbreaks 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 researchers 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 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 IPPC’s high carbon-emission model, the disease is likely to spread across most of the UK in the next 50 years.
Gradual warming
Professor Richard Nichols, co-author of the study from Queen Mary University of London, said: “The climate has been gradually warming over many years - that makes it difficult to say if an invasive disease has spread because it just happened to arrive in the UK recently, or because of the warming climate. We managed to overcome that problem by experimenting on this virus directly - finding out if it was more severe in laboratory conditions as we warmed up the experimental conditions.”
Dr Stephen Price, lead author from ZSL’s Institute of Zoology and UCL added: “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.”
The researchers 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.”