Ranavirus: update from Froglife

Dr Amber Teacher, formerly of the Institute of Zoology (ZSL), has outlined some of the findings from her research into ranavirus, a frog disease that appears in many UK gardens in the summer months.

Amber’s results are thanks largely to the interest and involvement of our supporters in providing data from their back gardens, through our Frog Mortality Project, for over fifteen years…

“Many people will have submitted reports of frogs found dead in your gardens to Froglife. These records have been archived over the years, and have been used for research into a viral disease called Ranavirus.

This disease can cause skin ulceration which can get so bad that the frogs’ limbs degrade. It can also cause haemorrhaging of the internal organs, though this is not visible from the outside. Ranavirus often causes ‘mass mortality events’, where a great number of frogs are found dead over a short time-span.

Studies by Dr Andrew Cunningham, a veterinary researcher based at the Institute of Zoology, have shown that this disease is likely to have been introduced from North America.

Some surprising results have come of this study – it seems that Ranavirus can have a range of possible effects on frogs.

The disease appears to be able to be cleared by some frog populations, to affect other populations on a yearly basis, or to cause local frog populations to die-off. This range of responses implies that some frog populations are better able to cope with the infection than others.

The researchers looked more closely at the populations that are affected by recurrent disease, and found that these frogs seem to be doing something rather strange – healthy frogs seem to be mating with healthy frogs, and diseased frogs seem to be mating with other diseased frogs.

It is generally thought that common frogs mate fairly randomly, and are not choosey about who they mate with. It is likely that the frogs that have been infected are not strong enough to mate with fit, healthy frogs, and so are left to mate with other infected frogs.

The researchers also looked at the genetics of the immune system in these diseased frogs. In particular they studied a gene which is directly linked to the frogs’ ability to cope with viral infections, and they found that this gene is different in frog populations that are affected by disease, compared to those that have never been affected by disease. This is the first evidence that wild common frogs might be adapting to cope with infection, and may indicate that they are capable of becoming immune over time.

However, although these are promising results for the long-term future for this species, the disease remains a major welfare issue which affects a great number of frogs. Also, whilst the frogs may eventually be able to resist infection, the process of specialising their immune systems to deal with Ranavirus may leave them more susceptible to other diseases.

Without the help of Froglife's supporters, this work would not be possible, so we are extremely grateful for your continued interest and support.”

Such collaborative research between Froglife and the Institute of Zoology is set to continue; there is another PhD project currently underway which is looking at which other species can be affected by Ranavirus. New links are also being forged with Imperial College London, where there is expertise on modelling the spread of diseases.

Froglife would like to thank those that contributed to our Frog Disease Appeal in late 2008 – and to Natural England for additional financial support for our data-entry officer, Sophie Webster.

The Frog Mortality Project is a joint project between Froglife and the Institute of Zoology (ZSL).

For more information on the Frog Mortality Project click here.

“Let garden ponds breath easy” says amphibian charity

As the cold snap continues, Froglife -a UK wildlife charity for amphibians and reptiles- is encouraging pond-owners to consider ensuring garden ponds don’t stay iced over for too long.

Common Frogs Rana temporaria often lie dormant on the bottom of garden ponds during winter, but when ponds ice over for a sustained period they can suffocate on the noxious gases that build up in the water. In some winters, many frogs can die from this phenomenon, often termed ‘winterkill’.

Winterkill is a natural killer of frogs in cold winters. Many garden owners choose to take steps to reduce winter mortality and keep their local frog populations thriving.

The solution is simple, say Froglife: “To stop winterkill happening in your pond simply ensure that there is a hole in the ice for pond gases to escape. You can make a hole by leaving a plastic ball in the pond overnight, and removing it in the morning when the pond surface is frozen. Another idea is to leave a pan of hot water on the ice surface, and allow the base of the pan melt a hole.”

“Importantly though, never pour hot water on the pond ice, and don’t add chemicals (particularly salt), or try to shatter the ice. All of these methods can cause serious damage to pond inhabitants,” said Lucy Benyon, Froglife’s Wildlife Information Officer.

In many parts of the UK, a number of amphibian species (frogs, toads, newts) are facing serious declines, largely because of the loss of ponds in the wider countryside. Urban areas have provided a crucial refuge for some species, thanks to an increase in the number of garden ponds in the last thirty years.

Amphibian populations could halve by 2050

Half of Europe's frogs and toads and newts could be wiped out in the next 40 years, scientists from the Zoological Society of London (ZSL) have warned.

Factors including climate change, habitat destruction and disease are having a serious effect, said ZSL scientists at a special event hosted by Sir David Attenborough on 25th September 2008.

Speaking at the lecture, Dr Trent Garner, a Research Fellow at ZSL, said climate change will dramatically affect the living conditions of amphibians and survival of populations:

“Published projections show that climate change alters amphibians’ habitats so we expect a large number of amphibian species to be faced with loss of habitat and ultimately extinction.” said Dr Garner.

“In the UK we are already seeing common toads losing condition and experiencing reduced survival. As climate change continues to impact habitats, the situation gets far worse for these native species.” he added.

In addition to identifying climate change as a threat, Dr Garner and his colleagues also highlighted two infectious diseases affecting survival rates, a chytrid fungus and ranaviruses. Ranavirus kills thousands of amphibians in the UK each year and the chytrid fungus, implicated in extinctions of amphibian species around the world, has recently been identified in the UK.

Froglife and the Institute of Zoology (based at ZSL) have been working on the issue of amphibian disease in the UK since 1992, through our Frog Mortality Project. Currently Froglife are running a Frog Disease Appeal so that the Frog Mortality Project can expand and better inform scientists of the disease threat, working toward a safer future for the UK's amphibians >>> Frog Disease Appeal…

Later this year solutions to the imminent extinction crisis facing the world’s amphibians will be discussed at another ZSL event: ‘Halting the Global Decline in Amphibians: research and practice’ – a two-day symposium being held on 20 & 21st of November 2008 >>> More details…