In the late 1980s, unusual mortalities of common frogs were reported in the south-east of England. Frogs were found to be suffering from a variety of symptoms, sometimes with secondary bacterial infections. The patterns of infection indicate that Ranaviral disease is relatively new to the UK, possibly spread from North America through the commercial importation of bullfrogs or goldfish.

Ranavirus seems to be found mainly in common frogs, occurring less commonly in other amphibians. It causes two forms of disease in frogs: skin ulcers and internal bleeding. In the first case ulcers can readily be seen on the skin, especially on the underside of the pelvic region and on the hind limbs and feet, in extreme cases causing loss of digits. Bleeding is sometimes evident from the mouth or cloaca or as a reddening of the underside. This reddening led to the name ‘red-leg’ disease, yet this is a misleading term for ranaviral disease: frogs with reddened legs may be ill due to some other infection, and frogs with ranaviral disease may exhibit other signs such as lethargy and emaciation.

Frogs can have the disease but show no clinical signs of infection. Similarly, you may see animals that are suffering from some of the symptoms, but there is another cause. Ranavirus is only active in warm temperatures, so dead animals found outside the summer months are more likely to have died from something else.

The clearest indications that a frog population is suffering from ranaviral disease are mass mortalities of adults in or around the pond in summer, particularly if you notice frogs that are very thin or lethargic a few days before.

Although Ranavirus can be devastating within an infected pond, we don’t yet understand its wider impacts on conservation status. Individual populations respond differently. In some cases mass mortalities are followed by population recovery, in others the disease is recurrent and there can be long-term declines of up to 80% (Teacher et al., 2010). Further studies are needed to determine the full significance of disease impacts.

Related Reading

ARG UK (2008) Amphibian and Reptile Groups of the UK Advice Note 4 (version 1): Amphibian disease precautions; a guide for UK fieldworkers. See publications section of

Duffus, A.L.J. and Cunningham, A.A. (2010). Major disease threats to European amphibians. The Herpetological Journal 20, 117-127.

Teacher, A.G.F., Cunningham, A.A. and Garner, T.W.J. (2010). Assessing the long-term impact of Ranavirus infection in wild common frog populations. Animal Conservation 13, 514-522.