British suburban gardeners may be unknowingly driving the spread of a lethal frog disease by stocking their ponds with exotic or wild aquatic species, research shows.
Scientists from ZSL and Queen Mary University of London say their findings could explain the rapid spread of ranavirus across UK amphibian populations in recent decades.
Ranavirus is thought to have been introduced at least twice since the 1980s - most likely from North America. The disease was first found in south-east England, but has since spread across the UK with recorded outbreaks in Cornwall, Cardiff, Lancashire and Newcastle.
While the pathogen spreads with the natural movement of amphibian populations, the expansion of its range appears to have been exacerbated by human-assisted movement of infected animals and contaminated materials between garden ponds and commercial aquatics retailers, the study found.
“Ranavirus is one of the most serious health threats currently facing the UK’s amphibian population, so our findings that humans seem to have helped move the virus around, facilitating its rapid spread, could be translated into some straightforward ways to manage the risk of disease outbreaks,” said lead author, Dr Stephen Price.
Well-meaning homeowners stocking their garden ponds with frogs, fish or spawn translocated from neighbouring ponds or beyond could inadvertently be fuelling the spread of this serious amphibian disease, he said.
“We certainly don’t want to discourage people from adding ponds to their urban gardens – this remains one of the most positive steps we can all take to support wildlife – but equally we would strongly urge people to try to limit how much potentially infectious material they’re moving into and out of their gardens in the process.”
All species are susceptible to ranavirus but it mostly affects Britain’s native common frog (Rana temporaria) and common toad species (Bufo bufo).
Outbreaks of the disease are characterised by large numbers of dead amphibians in water bodies or individual sick animals that show symptoms including reddening and ulceration of the skin, internal bleeding and loss of digits.
The disease is highly infectious and can survive in the environment for more than two months.
The study found the risk of disease was higher in areas of higher human density, and that fewer disease outbreaks occurred in less affluent neighbourhoods.
The work, which also involved University College London and Herpetofauna Consultants International and was published in the journal Proceedings of the Royal Society B, was based on two decades of citizen science data recorded by the Frog Mortality Project.