Salamander Chytridiomycosis

This fact sheet was updated on March 21st, 2020. 

Cause

Salamander chytridiomycosis is an infectious disease caused by the fungus Batrachochytrium salamandrivorans. The fungus is a close relative of B. dendrobatidis, which was described more than two decades ago and is responsible for the decline or extinction of over 500 species of frogs and toads. Salamander chytridiomycosis (Bsal), and the fungus that causes it, were recently discovered in 2013 (Martel et al., 2013). The first cases occurred in the Netherlands, with outbreaks in native fire salamanders, Salamandra salamandra, that resulted in the loss of over 96% of the population. Further work discovered that the fungus is present in Thailand, Vietnam and Japan, and can infect native Eastern Asian salamanders without causing significant disease (Martel et al., 2014); this indicates Bsal may be native (or naturally endemic) to this region. Evidence suggests that Bsal was introduced to Europe through imported exotic salamanders from Asia that act as carriers of the fungus. Once introduced the fungus is capable of surviving in the environment, amongst the leaf litter and in small water bodies, even in the absence of salamanders. It thrives at temperatures between 10-15°C, with some growth in temperatures as low as 5°C and death at 25°C.

Significance

To date, the fungus and associated disease have not been found in North America, but an introduction of the fungus into native salamander populations could have devastating effects.

A United States Geological Survey (USGS) risk assessment predicts that the greatest risk of an introduction of Bsal into the United States is in the Pacific Coast, southern Appalachian Mountains, and mid-Atlantic regions, with the overall risk being most significant across the eastern United States (Richgels et al., 2016). 

In Europe, the fire salamander population where the disease was first discovered is at the brink of extinction, with over 96% mortality recorded during outbreaks. Little is known about the susceptibility of most North American salamanders and newts but, based on experimental trials, at least two species, the Eastern newt (Notophthalmus viridescens) and the rough-skinned newt (Taricha granulosa), are highly susceptible to the fungus and could experience similar high mortalities. If B. salamandrivorans is introduced into North America, it will likely become permanently established and, based on experience with frog chytridiomycosis (Bd), impossible to eradicate.

Bsal is an OIE reportable disease. 

Species Affected

Based on experimental infections conducted on selected species of each of the three amphibian orders, Bsal seems incapable of establishing an infection in the skin of frogs (order Anura) and caecilians (order Caecillian), while it is deadly to the majority of species of salamanders and newts (order Urodeal) in which experimental infections have been performed. Three species of Asian salamanders have been proposed as potential reservoirs: the blue-tailed fire-bellied newt (Cynops cyanurus), Japanese newt (Cynops pyrrhogaster) and Tam Dao salamander (Paramesotriton deloustali).

There is no known zoonotic risk associated with Bsal.

Distribution

Salamander chytrid appears to be native to Eastern Asia, where it infects salamanders native to Thailand, Vietnam and Japan without causing significant disease. As of 2018, in Europe Bsal has been detected in wild salamanders in the Netherlands, Belgium, Germany, and Spain. In addition, Bsal outbreaks in captive salamander populations have been reported in the United Kingdom, Germany, the Netherlands, and Spain. 

Transmission

Chytrid fungi, including Bsal, can be transmitted through contact with water or organic matter (mud, leaf litter, etc.), or by direct contact with an infected salamander. Similar to Bd, Bsal produces motile zoospores, capable not only of surviving in water and moist environments, but also of short distance dispersal through active swimming. Because the fungus and its infectious zoospores can survive in the absence of an infected host, transmission from an outbreak site to adjacent areas can occur both through dispersal of infected salamanders and through human activities, such as movement of soil, water or even fishing bait.

Clinical Signs

Like the frog chytrid fungus, B. salamandrivorans infects only the skin, never going into deeper tissues. Clinical signs are similar to those seen in Bd and can include reddening and ulceration or blistering of skin, excessive shedding of skin, ataxia, apathy, emaciation, and ultimately death. Skin lesions are not always obvious. Disease severity is variable and may depend on climatic conditions, species infected, life stage infected, etc.

Diagnosis

Infection (presence of the fungus in a host) and disease (ill effects on the host) are not the same thing. Some species of salamanders, the Asian carriers for instance, can be infected but do not develop disease. To diagnose Bsal it is necessary to confirm the concurrent presence of skin lesions and the fungus. This is done through a combination of histologic (tissue) examination and molecular confirmation of the fungus (via PCR or qPCR).

Treatment

Research specific to treatment of B. salamandrivorans has only begun, and it has shown that controlling temperature may be a viable way to treat infected salamanders in captivity. Based on what is known of the frog chytrid (Bd) infection, several antifungal drugs could prove effective against Bsal, especially in captive individuals.

Management

As with frog chytrid fungus, Bsal could be spread during anthropogenic activities. Boots, clothes, and all field equipment should be cleaned and disinfected with appropriate cleaners/disinfectants according to product label, before moving between sites. Wild amphibians should not be moved between habitats, and captive amphibians should not be released into the environment or used as fishing bait. All newly acquired captive amphibians should be initially quarantined from other amphibians until it has been confirmed that they are disease free.

Suggested Reading

  • Martel et al. Batrachochytrium salamandrivorans sp. nov. causes lethal chytridiomycosis in amphibians. PNAS 110(38): 15325–15329 doi: 10.1073/pnas.1307356110
  • Amphibian Survival Alliance and Amphibian Specialists Group
  • Martel et al. 2014. Recent Introduction of a chytrid fungus endangers Western Palearctic salamanders. Science 346(6209): 630-631.
  • Richgels KL, Russell RE, Adams MJ, White CL, Grant EHC. 2016. Spatial Variation in Risk and Consequence of Batrachochytrium salamandrivorans Introduction in the USA. Royal Society Open Science, 3(2):150616
  • Bsals Europe
  • Bsal Task Force
  • https://www.cabi.org/isc/datasheet/121671
  • Yap, T.A., Koo, M.S., Ambrose, R.F., Wake, D.B., Vredenburg, V.T. (2015) Averting a North American biodiversity crisis. Science 349(6347):481-482 doi:10.1126/science.aab1052
  • Sabino-Pinto J et al. 2015. First detection of emerging fungal pathogen Batrachochytrium salamandrivorans in Germany. Amphibia-Reptilia 36(4): 411-416.

Images

Bsal vulnerability model for North America (2015)Bsal vulnerability model for North America (2015)
Skin lesions in Bsal infected salamanderTypical skin lesions in Bsal infected salamander
A native rough skinned newt, Taricha granulosa. Bsal is considered lethal to this species. A native rough skinned newt, Taricha granulosa. Bsal is considered lethal to this species.