A disease that causes mass die-offs in frogs has been found in captive UK populations for the first time, scientists have warned.
Severe perkinsea infection (SPI) has caused large tadpole mortality events across the US, and this is the first proof that its geographic range is spreading. Researchers also found the disease-causing microbe in wild and seemingly healthy populations in Panama, where some of the most rapid declines in frog populations globally have occurred.
“This has alarming implications for conservation, as many amphibian species are suffering catastrophic population decline,” the researchers say in their paper, published in Biology Letters. The disease causes bloating in frog tadpoles, leaving them unable to dive, and leading to rapid death from multiple-organ failure. Separate research suggests the infection causes more than 95% mortality in affected populations.
The disease was found in European tree frogs bought from a pet store and kept in an aquarium in Surrey. It probably came in via contaminated tank water or equipment, but it is almost impossible to trace the source. Currently, there is no evidence of SPI in wild amphibian populations in the UK or Europe, but there has been little testing. “Where we’ve looked, we’ve seen it,” said Prof Tom Richards from the University of Oxford, one of the paper’s authors.
Nearly one in three amphibian species is threatened with extinction, and emerging infectious disease, along with habitat destruction, is the main driver of decline. There is no cure for SPI, which was first detected in New Hampshire in 1999 and is now recognised as one of the most significant causes of mass mortalities among tadpoles in the US.
To do the research, scientists ethically euthanised tadpoles and dissected liver tissue, which is the primary site of infection. They then used a DNA detection method to see if the parasite was present. Ten of the 81 tadpoles tested in Panama had the SPI-causing protist organism, referred to as the pathogenic perkinsea clade (PPC). Five of 10 tadpoles taken from the UK aquarium where the tree frogs were breeding had it.
Researchers did not wait to see whether the disease developed in populations in Panama, whereas in the UK aquarium population, tadpoles had already developed the disease, which is why the aquarium owner contacted the team. The causal link between the PPC pathogen that causes SPI disease has yet to be proved but existing literature shows a “strong association”, said Richards.
Researchers are calling for large-scale screening of amphibian populations, particularly those being traded, to monitor disease and reduce the risk of spread.
“If we wait for more experimental tests and don’t change policy [on screening for disease] then it’s too late. I find this all very reminiscent of the Covid situation – ‘Oh it’s coming, it’s coming, we’re not sure if it’s a real threat yet’ – then it’s too late,” said Richards. “Obviously, the world cares a lot less about frogs, but maybe it should care a bit more.
“Wider food webs depend on frogs, take out one element of the web and the whole thing collapses,” said Richards, who has set up a UK website called Tadpole Doctor so that people can help to identify potential disease early. Next, researchers want to test for the disease in India, other areas of Europe and northern Australia.
The international trade in frogs for meat and for zoological and private collections is very large. More than $100m (GBP70m) a year is spent on the trade in meat alone of just two frog species. Disease flourishes when habitats are destroyed and populations that wouldn’t naturally meet are put in contact with one another, often in highly stressful conditions.
Dr Mark Wilber, an ecologist from the University of Tennessee who was not involved in the research, said: “Hundreds of amphibian species have had, or currently are experiencing, population declines due to infectious disease.