Amphibian disease

Worldwide, one third of all amphibian species are thought to be threatened with extinction and many others face severe population declines. Habitat loss is the main cause of declines worldwide, but there is growing concern surrounding the threats posed by infectious disease.

Growing numbers of amphibian diseases have been described in recent years. The most notable of these are chytridiomycosis and ranavirus: 

• Chytridiomycosis is caused by two species of microscopic fungi Batrachochytrium dendrobatidis (“Bd”) and B. salamandrivorans (“Bsal”), which are often simply referred to as “chytrid”. Chytrid infection has been responsible for mass mortalities of amphibians with declines and extinctions in some species on six continents, including Europe.
• Ranavirus (ranaviral disease), caused by infection with one of many types of ranavirus, also has a wide global distribution, though it appears to cause population declines less frequently than chytridiomycosis
• Other infectious agents, about which much less is known, include herpesvirus and the parasitic infections Amphibiocystidium and Ribeiroia. It is likely that additional, currently undescribed, diseases will emerge in the future.

In the UK, a number of pathogens and infected amphibians have been detected, yet the implications for conservation remain largely unclear. For example, whilst Bd is now known to be widespread in Great Britain, it does not appear to have caused the types of mass die-offs reported overseas. However, the lack of evidence for mass mortalities should not lead to complacency; such events can be difficult to detect even when they are occurring, and it can take many years for the full effects of disease introduction to manifest. Whilst Bsal is known to be present in captive amphibians in the UK, it has not yet been detected in the wild. However, it is believed to be a major potential threat to newt health should it become established, particularly the great crested newt which is known to be highly susceptible.

Three key findings from research underpin our advice (1) amphibian diseases are frequently found to be spread by human activity, and amphibian fieldworkers therefore have a particular responsibility (2) amphibian disease emergence is commonly associated with the introduction of non-native species; and (3) signs of infection are not necessarily evident on visual inspection.

As a consequence we are constantly reviewing our biosecurity guidance which can be downloaded here and should be cited as:  ARG UK (2017).  ARG UK Advice Note 4: Amphibian Disease Precautions: A Guide for UK Fieldworkers. Amphibian and Reptile Groups of the United Kingdom.

Presently there is no evidence to suggest that amphibian diseases found in the UK present a hazard to human health.