The pathogenic fungi Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans and risk of negative impact on biodiversity


Report no: 2019:04

Published: 15.05.2019

Key message:

The risk of a negative impact on amphibian diversity in Norway stemming from the two pathogenic fungi Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal) is moderate and small, respectively. An outbreak of Chytridiomycosis will have a limited impact on biodiversity in general but could affect local populations.

The Scientific Committee for Food and Environment (VKM) has come to this conclusion after conducting a risk assessment of these fungi. The Norwegian Environment Agency commissioned the assessment.

High risk globally

The fungi can cause Chytridiomycosis in amphibians. This disease has resulted in the massive decline of amphibians in many countries, and caused extinction of a number of species.

There are only a few indigenous amphibian species in Norway. The most common ones are great newt, smooth newt, common frog, moor frog and common toad. Scientific studies from other European countries show a low rate of disease in these species, even when infected. The species found in Norway appear to be less susceptible than many other species. The cold climate could play a role.

Batrachochytrium dendrobatidis (Bd)

Batrachochytrium dendrobatidis (Bd) is one of the most devastating pathogen fungi to infect wild animals. VKM has concluded Bd poses a moderate risk to the amphibians in Norway.

-It is likely that Bd will further establish itself and spread in Norway, as it is already present here, and is widespread in Sweden, says Anders Nielsen, chair of the working group.

He points out that establishment and proliferation will affect the various amphibian differently.

-The effect on the common toad and pond frog is considered moderate. These species are more susceptible for the disease than the other species in Norway. The fungi might lead to individual deaths and possibly to a reduction of local populations.

-The effect on the common frog is considered low. For the moor frog, great crested newt and the smooth newt, the effect is considered minimal. There are very few, or no documented effects of Bd-infection on these species, says Nielsen.

Batrachochytrium salamandrivorans (Bsal)

VKM concludes that Bsal poses a small risk to the amphibians in Norway.

-It is unlikely that the fungi will establish itself and proliferate in Norway, as it has not been detected in any of our neighboring countries. In addition, the import of amphibians is prohibited in Norway, which decreases the likelihood of the pathogen entering the country, says Nielsen.

Bsal mainly infects salamanders, but as of now, only the fire salamander is severely impacted in Europe. Should the pathogen arrive in Norway, VKM concludes that the effects on both the great crested newt and smooth newt will be small.

-There is no documented cases of Chytridiomycosis on these species. Also, the geographic structure of our populations, and low connectivity between these, is likely to impede the spread of Bsal, according to Nielsen.

Mitigation measures

Both fungi are introduced predominantly through human activities, such as trade and release of exotic species, but also through translocation of infected individuals of indigenous species from neighboring countries. They spread from human activities and on their own.

Import, trade, keeping and release of amphibians is prohibited in Norway. It may be effective to implement information campaigns to raise awareness in the public on how these pathogenic fungi are introduced and spread.

-It is impossible to eradicate Bd or Bsal once established, but further proliferation can be reduced to some degree by taking effective mitigation measures, says Nielsen.


This risk assessment is characterized by uncertainty. We know little about the natural spread of the fungi in nature, and especially how an infection is affected by other factors such as habitat change, environmental pollution and climate change. VKM points out that an increase in water temperature will increase the likelihood of an outbreak.

There is also limited knowledge of the total distribution and population sizes of the amphibians in Norway. Only the great crested newt is to some degree monitored.

-This makes it hard to detect any gradual changes in wild amphibian populations, says Nielsen.

The Panel on Alien Organisms and Trade in Endangered Species (CITES) of the Norwegian Scientific Committee for Food and Environment is responsible for the evaluation of the project.


Anders Nielsen

Co-chair for the Panel for Alien Organisms and Trade in Endangered Species (CITES). Phd.

M: 91 35 04 35

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