Amphibians are the most threatened class of vertebrates worldwide. In addition to biotope changes, fungal infections in particular lead to population collapses. The "salamander eater" or "salamander plague", a fungus(Batrachochytrium salamandrivorans), infects the skin of amphibians and leads to death, especially in caudates such as salamanders and newts.

Worldwide, the fungus was introduced from Asia to Europe via trade with caudates

Endangered host animals are amphibians, especially tailed amphibians; frogs show no symptoms but can be carriers of the fungal infection. In several European countries (Germany, Belgium - last outbreak in 2024 - , Spain, the Netherlands and the UK), salamanders have already died out en masse in the wild, leading to the extinction of entire populations in the infested regions

In captivity, the fungus is transmitted to healthy animals by infected animals, by furnishings and animal by-products from fungus-infected terrariums. In the field, the fungus can be introduced into a biotope via migrating caudates and frogs, via birds, via animals visiting the biotope and via humans.

7 days

Highly contagious infection that usually leads to death in caudates after more or less pronounced clinical symptoms (skin lesions, skin ulcers). Death occurs in caudates 12-18 days after infection or 7 days after the first symptoms appear.

Tail amphibians in captivity can be treated with special fungicides. Treatments have proven effective at the same time increased holding temperature

The EU is considering a trade and import ban on caudates from Asia. Tail amphibians purchased or bought in the trade must be carefully examined for fungal infections. They should be kept separate from existing captive animals by means of quarantine for the time being. Animal by-products associated with the keeping of caudates must be subjected to a heat treatment (10 days at 25 °C). Furnishings from terrariums that have come into contact with infected animals should be thoroughly cleaned and disinfected before reuse.

The University of Veterinary Medicine carried out active monitoring in 2016-2017 and 2023; there are currently no known infestation regions in Austria

Batrachochytrium salamandrivorans (Bsal), is a pathogenic fungus (genus: Batrachochytrium, order: Rhizophydiales, class: Chytridiomycetes) that mainly affects tailed amphibians - salamanders and newts. In regions where the fungus has already been detected, these amphibians are considered endangered species due to mass mortality following fungal infections. Bsal has been detected in animals in the wild and in captivity in Germany (region: Eifel, Ruhr area - Essen area, Bavaria; 2018), Belgium (2013, 2024), Spain, the Netherlands (2008, 2013) and the UK. According to EU Regulation 2018/1629, the disease is classified as an animal disease and is therefore notifiable.

B. salamandrivorans originates from Asia (Japan, China and Southeast Asia) and is not dangerous for the amphibian fauna there. In the course of evolution, Asian amphibians have been able to adapt to the fungus. They show only mild symptoms. However, the fungus is new to European tailed amphibians; the animals become infected, fall ill and die. Infection of healthy animals can occur directly via contact with sick animals or indirectly via contaminated water through mobile zoospores or substrate. The fungus occurs in Europe in the wild and frequently in terrariums. The fungus was probably introduced to Europe via the global trade in exotic species of tailed amphibians and toads(Bombina microdeladigitora, Hubel's red-bellied toad). Exact details are not known, but trade remains the number one source of danger.

B. salamandrivorans (Bsal, salamander eater or salamander plague) is closely related to B. dendrobatidis (Bd, chytrid fungus). Both belong to the class Chytridiomycetes, the order Rhizophydiales and the genus Batrachochytrium. In contrast to the chytrid fungus, Bsal forms a thallus with germ tubes. It occurs frequently in the form of colony-forming thalli. When mature, the thallus consists of a sporangium with germ tubes and rhizoids. The zoospores in the sporangium are mobile and serve to spread the fungus. The epidermis of healthy animals is infected by the zoospores. There are also permanent spores that are resistant to environmental influences and can survive unfavourable environmental conditions in the soil or water for long periods of time. The optimum ambient temperature for Bsal is 10-15 °C, after 5 days at 25 °C the fungus dies.

B. salamandrivorans poses a threat to the biodiversity of the European amphibian population. There is no known antidote against the spread of the fungus; infected populations must be considered lost. Experts have been commissioned by the EU to set up a European warning system for the spread of the pathogen. Some European countries are carrying out nationwide monitoring (e.g. the Netherlands and the Czech Republic). In Austria, active monitoring was carried out by the University of Veterinary Medicine in 2016-2017. The EU recommends the establishment of passive monitoring teams that work according to a harmonised protocol. In some European countries with established infestation regions, tailed amphibians are even removed from the population and transferred to a conservation breeding programme.

Import restrictions have been implemented in Switzerland and Hungary. In 2018, the European Commission temporarily imposed trade restrictions on the import of salamanders from third countries. However, these do not regulate the import of anurans, which can act as carriers of Bsal. Illegally released, possibly infected animals in the wild are an increasing source of danger for the amphibian population.

Symptoms

The following tailed amphibian species have been shown to be affected by Bsal infection (see also EFSA 2017 Appendix E): the fire salamander(Salamandra salamandra), the North American fire salamander(S. algira), the Corsican salamander(S. corsica), the Asia Minor salamander(S. infraimmaculata), the Alpine (mountain) newt(Ichthyosaura alpestris), the pond newt(Lissotriton (syn. Triturus) vulgaris) and the thread newt(L. helveticus). The infection is highly contagious and is almost always fatal for tailed amphibians. The disease can progress rapidly or, as in the Alpine newt, slowly. An infection in a biotope usually leads to the total loss of the population in combination with other unfavourable factors. A pathological infection of frog amphibians (frogs and toads) is not yet known. However, frogs (e.g. the midwife toad Alytes obstetricans) can be intermediate hosts. They can carry the fungus on their skin and thus presumably act as a reservoir and vector.

Clinical symptoms in tailed amphibians: Only adult animals are affected, as the skin fungus attacks the keratin-containing components of the skin, which are still missing during the larval stage. Infections with Bsal in fire salamanders can usually be recognised by circular, black-bordered, superficial skin lesions as well as deep skin ulcers. The skin ulcers are often colonised by bacteria. The severity of the skin lesions varies depending on the amphibian species. In newts, a more or less long symptom-free course of the disease is possible. 12-18 days after injection or 7 days after the first symptoms appear, death occurs in tailed amphibians after a short phase of anorexia (loss of appetite), ataxia (impaired coordination of movement), lethargy and apathy (apathy).

Preventive measures

• Do not catch frogs, toads, newts and salamanders and do not move them from one location to another, e.g. to stock a garden pond
• Never release animals and plants from garden ponds, terrariums or pet shops into other bodies of water in nature or in the garden - even if they are native species. Do not dispose of waste water and/or furnishings from terrariums or aquariums in the garden or in the wild
• Do not touch any free-living amphibians. Please also do not pick up any dead animals - report any dead animals that are not found on a busy road to the relevant authorities so that they can arrange a test for Bsal. Infection with Bsal is notifiable
• Clean your footwear thoroughly after or before an excursion into nature to remove any adhering soil - especially if you have been in the vicinity of amphibian sites. Do not visit several amphibian sites without disinfecting after each visit. If you have previously travelled in other countries or regions, please disinfect the soles of your shoes
• If your vehicle has come into contact with water and damp soil off-road at an amphibian site, at least clean the tyres thoroughly with water (or disinfectant) before changing locations. Have your amphibians in terrariums or aquariums tested regularly for infection with Bsal and Bd

Diagnostics: https://www.vetmeduni.ac.at/klivv/ueber-uns/unser-team/wissenschafter/smith-steven/chytrid-schnelltestungen

Fire salamander species conservation project: https://www.zoovienna.at/natur-und-artenschutz/artenschutzprojekt-feuersalamander/

Information WOAH: https://www.woah.org/en/disease/chytridiomycosis-batrachochytrium-salmandrivorans/ 

Skin lesions are not always visible in the early stages of infection, but usually only shortly before death. Molecular biological analyses (duplex qPCR, EFSA 2018) must therefore often be carried out in suspected cases. Skin swabs are the preferred sample material for live animals. Mixed infections of Bsal and Bd occur.

The ELISA technique or cultivation of the fungus often leads to inaccurate results or false negative results and is therefore not recommended as a diagnostic tool (see EFSA 2017). Testing for Bsal is currently carried out using molecular biological methods.

In nature, Bsal infections are usually only recognised after death. In the event of death, a histological examination of the skin lesions can be carried out in addition to the molecular biological analysis. While chytrid fungal infections only result in hyperplasia or hyperkeratosis, fungal infections with Bsal also result in deep ulcers distributed over the body. The keratinocytes at the edges of the lesions are necrotic and contain a thallus.

Molecular biological testing for chytridiomycosis: Steven Smith, Konrad Lorenz Institute for Comparative Behavioural Research, Department of Interdisciplinary Life Sciences, University of Veterinary Medicine Vienna, Savoyenstr. 1a, A-1160 Vienna, steve.smith@vetmeduni.ac.at