Science last week had the latest on the new chytrid fungus, Batrachochytrium salamandrivorans. This fungus was discovered after it wiped out Fire Salamanders (Salamandra salamandra) on a Dutch nature reserve in 2010. It is distinct from B. dendrobatidis, the species that is devastating frogs and toad populations throughout the world. A multinational team reported in Science the results of their exposing specimens of 35 captive-bred or wild caught amphibian species to the new fungus. The results were clear. The anurans, or, if you prefer, salientians, in other words the frogs and toads, were not affected nor was the one gymnophionan or caecilian tested. But nearly all the urodeles, or caudates, were, and died rapidly after infection. These results were confirmed by looking for the organism’s DNA in the skin of 5391 wild amphibians. It was found only in urodeles and only in ‘East’ Asia (Thailand, Vietnam and Japan) and in those European countries (Netherlands and Belgium) where the severe disease outbreaks were observed.
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| Salamandra salamandra - this one is in Hungary |
The infection experiments indicated that three Asian urodeles tested could act as reservoirs of the disease: Cynops pyrrhogaster, Cynops cyanurus and Paramesotriton deloustali. Seven specimens either limited the effect of the clinical disease or completely eliminated the infection. The authors calculate that the two chytrids diverged about 67 (mean) million years ago and that the potential of the ancestors of modern Asian newts to be a disease reservoir evolved between 55 and 34 million years ago. B. salamandrivorans was also found in a museum specimen of Cynops ensicauda at least 150 years old, supporting the view that the Asian species have greater tolerance to infection and constitute a reservoir through which species in other parts of the world could be fatally infected.
In a survey of wild amphibians, the organism was found only in East Asian urodeles—4% of the specimens of the latter species.
Because of the organisms apparent presence only in Asia, movement of amphibians in trade or for research appears to be responsible for the outbreaks in Europe. However, surveys done of urodeles at exporters, going through Heathrow airport or in pet shops found no infected individuals in the 542 tested. Another survey, this time of individuals established in captivity, found 3 specimens out of 408 infected; all were Tylotriton vietnamensis while 15 of the same species were uninfected.
These figures suggest to me that the importation of infected animals into Europe or the USA has been relatively uncommon. If the number of infected animals arriving had been greater then might we not have seen an outbreak in Europe earlier than the 21st Century? Vast numbers of East Asian urodeles have entered Europe from at least the early decades of the 20th Century, particularly Cynops pyrrhogaster and, more recently, Cynops orientalis. One out of 116 wild C. pyrrhogaster was found to be infected. Unfortunately no wild specimens of Cynops orientalis, probably the commonest urodele now in the aquarium trade, were tested. Of those in sampled at exporters, at Heathrow or in pet shops (including 11 C. pyrrhogaster and 145 C. orientalis) no infected individuals were found.
In the 1920s to the 1970s at least, C. pyrrhogaster was often kept by amateur herpetologists with native newts in indoor and outdoor vivaria. The opportunities for an infection of B. salamandrivorans to escape into wild newt and salamander populations must have been very great especially since surplus native species were often released into the wild. The authors of the paper in Science state that 2.3 million Cynops orientalis were imported into the USA between 2001 and 2009. Is it not likely that if this species were a common reservoir for B. salamandrivorans that the odds are that there would already have been an outbreak of the disease in the USA? But, however common or uncommon the infective agent is in the wild, in trade, or in specimens established in captivity, it is the fact that it is there at all, with its potential to devastate urodele populations in other parts of the world, that has given rise to great concern.
Given that the Netherlands has always been an epicentre of the amphibian and reptile trade and of expertise in keeping and breeding these animals, could it perhaps be the case that some of the species that became more common in captivity since the 1980s have a higher proportion of carriers than C. pyrrhogaster, for example? The detected occurrence in a species of Tylotriton would support this argument. Therefore, we may have the scenario in which a Dutch urodele enthusiast, passed infection to his or her captive European salamanders, which he then released into the wild. Or, he may have handled his infected individuals and then handled salamanders in the wild. Whatever the scenario, herpetologists, or somebody keeping urodeles as pets, have again unwittingly caused devastation to a wild population that could lead to extinction. Nobody anywhere predicted the presence of pathogenic chytrids.
It is not surprising, given the devastating effects of infection on non-Asian urodeles, that there have been calls to ban the movement of urodeles (as well as anurans because of the effects of mixing strains of B. dendrobatidis) between continents, although it has to be said that the movement of herpetologists and tourists between continents is also hazardous. The authors of the papers in Science conclude:
Our study demonstrates that the process of globalization with its associated human and animal traffic can rapidly erode ancient barriers to pathogen transmission, allowing the infection of hosts that have not had the opportunity to establish resistance. Thus, pathogens, such as those we describe here, have the potential to rapidly pose a threat of extinction.
In a separate commentary in Science this point is stressed in relation to a potential outbreak in the susceptible species of the USA where there is a war of words between the conservation lobby which evokes the precautionary principle to advocate a complete ban on imports and the pet trade (Cynops orientalis is very much part of the aquarium novelty trade). It is also pointed out that the US has no mechanism to control the import or sale of infected amphibians.
Will we continue to see amphibians included in the fancy aquarium fish trade? Will pre-shipment testing, quarantine and prophylactic treatment be sufficient? Eventually, I suspect, the trade in wild, ranched or captive-bred amphibians will be further restricted and very tightly controlled; the risk of doing nothing will be deemed too high. Time will tell if eventually is too late, or if the horse has already bolted.
Here is a very short video of Salamandra salamandra in the wild in Hungary in 2010:
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