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Possible differences in pathogenicity between cane toad-, frog- and platypus-derived isolates of Mucor amphibiorum,
1School of Medicine, University of Tasmania, Hobart, Tasmania, Australia. nstewart@utas.edu.au
Abstract:
Platypuses (Ornithorhynchus anatinus) in the north of the island state of Tasmania, Australia, suffer from a serious disease called ulcerative mycosis, which is responsible for high morbidity and, presumably, mortality rates in areas where it occurs. The disease is caused by the dimorphic fungus Mucor amphibiorum, which is also found in Queensland, New South Wales and Victoria. However, it does not cause disease in platypuses in those states. It has been previously reported that a closely related fungus, Mucor circinelloides, may also be capable of causing this disease. This paper describes pathogenicity trials involving cane toads (Bufo marinus) as the experimental model. The toads were infected with either Tasmanian, platypus-derived M. amphibiorum, West Australian, frog-derived M. amphibiorum, Queensland cane-toad-derived M. amphibiorum or Tasmanian platypus-derived M. circinelloides. The Tasmanian isolates of M. amphibiorum were more likely to cause a serious, long-term infection than were Queensland or West Australian isolates, and (+) mating types caused a more serious infection than the (-) mating type. The isolate of M. circinelloides was incapable of infecting the toads, lending further weight to the theory that it represents an environmental contaminant. The results suggest that an endemic strain of M. amphibiorum has mutated and become pathogenic to platypuses. Alternatively, a pathogenic strain of M. amphibiorum may have been introduced into Tasmania, where it is infecting a naïve population.
Insights
A fungal disease, ulcerative mycosis, severely impacts Tasmanian platypuses. Pathogenicity trials suggest a mutated or introduced strain of Mucor amphibiorum is responsible for this platypus disease.
Area of Science:
- Mycology
- Veterinary Pathology
- Wildlife Disease
Background:
- Platypuses (Ornithorhynchus anatinus) in Tasmania are affected by ulcerative mycosis.
- This disease, caused by Mucor amphibiorum, leads to high morbidity and mortality.
- The fungus is present in other Australian states but does not cause disease in platypuses there.
Purpose of the Study:
- To investigate the pathogenicity of different Mucor amphibiorum isolates in platypuses.
- To determine if Mucor circinelloides is a causative agent of ulcerative mycosis.
- To explore the origins of the pathogenic M. amphibiorum strain in Tasmania.
Main Methods:
- Pathogenicity trials were conducted using cane toads (Bufo marinus) as an experimental model.
- Toads were infected with M. amphibiorum isolates from Tasmania, Western Australia, and Queensland, as well as M. circinelloides from Tasmania.
- Different mating types of M. amphibiorum were also tested.
Main Results:
- Tasmanian M. amphibiorum isolates caused more severe, long-term infections than isolates from other regions.
- (+) mating types of M. amphibiorum were more virulent than (-) mating types.
- Mucor circinelloides did not infect the toads, suggesting it is an environmental contaminant.
Conclusions:
- Results indicate an endemic M. amphibiorum strain may have mutated to become pathogenic to platypuses.
- Alternatively, a pathogenic M. amphibiorum strain might have been introduced to Tasmania, infecting a susceptible platypus population.
- Mucor circinelloides is unlikely to be a cause of ulcerative mycosis in platypuses.
