Garden Ponds Could Aid Spread of Disease in Frogs

photo of a common Frog with its head just above water

A recent study has suggested that garden ponds could play a significant role in the spread of ranaviruses, diseases which infects amphibians, reptiles and fish. These diseases have devastated frog populations in the UK in recent years.

The latest research suggests that introducing infected animals from aquatic retailers into ponds or moving species between ponds could be helping the diseases to spread. The research has demonstrated that ranaviruses are spreading much faster than would be possible with frogs moving about of their own volition.

What are Ranoviruses?

Ranaviruses are a group of viruses found across the globe and they affect the various aquatic species in different ways. In the UK, one strain of ranavirus was found to be present in the South East of England in the 1980s and then spread swiftly across the region. The disease causes blisters to form on the frogs’ skin and their internal organs to bleed. It can persist amongst sections of the frog population and where it does, the population declines by up to 85% and then struggles to recover.

The Frog Mortality Project

In order to understand how ranaviruses spread, scientists examined 20 years’ worth of data recorded in a scheme called the ‘Frog Mortality Project’. This was set up in response to the outbreak of ranavirus in the 1980s and was partnership between the Institute of Zoolology (IoZ) and Froglife. The project collected disease reports and collated information regarding the deaths of over 85,000 frogs.

The work eventually evolved into The Garden Wildlife Health project, a joint enterprise involving IoZ, the Royal Society for the Protection of Birds (RSPB) and the British Trust for Ornithology (BTO). If you suspect that a frog in your garden has become a victim of ranavirus then this should be reported to the Garden Wildlife Health project. The symptoms to look out for are:

  • Drowsiness
  • Abnormal emaciation
  • Redness of the skin
  • Skin ulcers or sores
  • Bleeding, especially from the mouth and anus
  • Limb necrosis
  • Eye problems

The Research

Genetic analysis has suggested that ranavirus was not always present in this country and has been introduced on two different occasions. It was found that infection is spread by the natural movement of animals but that garden ponds could also be promoting the spread of the disease. The ponds act like stepping stones and enable infected animals to reach new areas.

People who take frogspawn or frogs from a pond and move them to another could be contributing to the spread of infection. Stocks of ornamental fish in ponds may also carry ranaviruses and their role in the transmission of disease might have to be investigated.

The Future of Pond Management

Experts have stressed that it would be wrong to discourage garden owners from featuring ponds on their properties as ponds are generally beneficial to wildlife. However, better husbandry should be encouraged. It is important that pond owners do not speed up the spread of infection and so should avoid adding potentially infected amphibians to their ponds.

Header photo – ‘Frog’ by Thomas Wood via Flickr (CC BY 2.0)

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