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.
Endangered hosts are amphibians, especially caudates; frogs do not show any symptoms, but may be carriers of the fungal infection. In several European countries (Germany, Belgium, Spain, the Netherlands, Great Britain), mass mortality of salamanders has already occurred in the field, resulting in 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.
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.
Batrachochytrium salamandrivorans (Bsal), is a pathogenic fungus (genus: Batrachochytrium, order: Rhizophydiales, class: Chytridiomycetes) that mainly affects caudate 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), Spain, the Netherlands (2008, 2013), and the United Kingdom.
B. salamandrivorans originates from Asia (Japan, China and Southeast Asia) and is not dangerous for the local amphibian fauna. In the course of evolution, the amphibians of Asia were able to adapt to the fungus. They show only minor symptomatology. However, the fungus is new to European caudate species; the animals become infected, fall ill and die. Infection of healthy animals can occur directly through contact with diseased animals or indirectly through contaminated water by mobile zoospores or substrate. The fungus occurs in Europe in the wild and clustered in terrarium husbandry. Presumably, the fungus was introduced into Europe via global trade in exotic caudates and toads(Bombina microdeladigitora, Hubel's fire bellied toad). Exact details are not known, and trade remains the number one source of danger.
B. salamandrivorans is closely related to B. dendrobatidis (chytrid fungus, Bd). Unlike the chytrid fungus, the fungus forms a thallus with germ tubes. It occurs clustered in the form of colony-forming thalli. When mature, the thallus consists of a sporangium with germ tubes and rhizoids. The zoospores located in the sporangium are motile and serve to disseminate the fungus. The epidermis of healthy animals is infected by the zoospores. In addition, there are permanent spores, which are resistant to environmental influences and can survive unfavorable environmental conditions in the soil or water for a long time. The optimal 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. The EU has commissioned experts to set up a European warning system for the spread of the pathogen. Some European countries conduct nationwide monitoring (e.g., the Netherlands and the Czech Republic). In Austria, active monitoring was conducted by the University of Veterinary Medicine in 2016-2017. The EU recommends the establishment of passive monitoring teams working according to a harmonized protocol. In some European countries with already established infestation regions, even caudates are removed from the population and transferred to a conservation breeding program.
Import restrictions have been implemented in Switzerland and Hungary. In 2018, temporary trade restrictions on the import of salamanders from third countries were adopted by the European Commission. However, these do not regulate the import of anurans, which can act as carriers of Bsal. Illegally released animals in the field, which may be infected, are increasingly sources of danger to the amphibian population.
Infection with Bsal has been shown to affect the following caudate species (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 threadfin newt(L. helveticus). The infection is highly contagious and is almost always fatal to tailed newts. The disease may show a rapid course, or as in the case of the Alpine newt, a slow course. An infection event in a biotope, in combination with other unfavorable factors, usually leads to the total loss of the population. A pathological infection of frogs (frogs and toads) is not known so far. However, frog amphibians (e.g., the midwife toad Alytes obstetricans) may be intermediate hosts. They may carry the fungus on their skin and thus presumably act as reservoirs and vectors.
Clinical symptoms in caudate toads: Only adults are affected because the cutaneous fungus attacks the keratinous components of the skin, which are still absent during the larval stage. Infections with Bsal in fire salamanders are usually recognized by circular, black-rimmed, superficial skin lesions as well as deep skin ulcers. The skin ulcers are often colonized 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 caudate amphibians after a short period of anorexia (loss of appetite), ataxia (disturbances in movement coordination), lethargy and apathy (apathy).
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. Preferred sample material in live animals are skin swabs. Mixed infections of Bsal and Bd occur.
The ELISA technique or cultivation of the fungus often leads to inaccurate results or false negatives and is therefore not recommended as a diagnostic tool (see EFSA 2017).
In nature, Bsal infections are usually only noticed after deaths. In case of death, histological examination of the skin lesions can still be performed in addition to molecular biological analysis. While infestation with the chytrid fungus only results 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.
Last updated: 20.04.2023