The Australian Cane Toad

.. field. Research and Control The CSIRO Australian Animal Health Laboratory (AAHL) at Geelong is a high security microbiological facility, purpose designed and operated to undertake research into viruses, bacteria, fungi and parasites which are exotic and do not occur in Australian domestic or wild animals. It is the only laboratory of its kind in Australia where studies on these exotic micro-organisms can be undertaken. Recently, the laboratory has been commissioned and funded to begin research into the control of the cane toad, using viruses or other microbial agents found overseas.

The major concerns about the toad involve its prodigious appetite, and the toxicity of all its life stages to native animals. There are firmly held beliefs that these characteristics of the cane toad are responsible for the deaths of Australian wildlife including herpetofauna, mammals, and fish. The toad will almost certainly establish itself throughout the sensitive wetlands of northern Australia. The Australian Government has provided significant funds to gather data to determine whether the toad has an impact on the Australian environment and whether a biological control agent is required. The funding also encompasses the search for and assessment of possible control agents.

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Funding of the project is distributed through the CSIRO Division of Wildlife Ecology, Canberra, upon the advice of the Cane Toad Research Advisory Committee. Current work to investigate the control of the cane toad by biological means has evolved from extensive studies over the past decade which have gathered basic ecological and disease data for the species. Such studies have been conducted in Australia, Venezuela, and Brazil. A search for microbial agents with potential for control of toads has recently been concluded in Venezuela. Research into the potential of viruses to control cane toads involved isolating and purifying viruses from cane toads in their native habitats of Venezuela, in South America. The effects of the viruses on cane toads and native frog species were then tested in the secure biocontainment facilities at the CSIRO Australian Animal Health Laboratory.

Dr Alex Hyatt from CSIRO Animal Health says viruses isolated from Venezuelan cane toads were compared with other viruses of the same family from around the world, and are believed to fall within a new species of virus. While the viruses proved effective in killing cane toad tadpoles, they also killed one species of Australian frog in the trial. The team also found a small percentage of Australian cane toads in the wild had been exposed to a virus similar to the Venezuelan viruses, which are known to cause disease and death in fish and amphibian populations in Australia and overseas. This adds another dimension to the potential impact of cane toads on the Australian environment, Dr Hyatt says. As part of the work, the researchers also identified two fungal pathogens that are lethal to cane toads and other amphibians.

One fungus is thought to be responsible for frog fatalities in Australia and Panama. Research also shows a small number of Australian cane toads may be carrying a virus similar to the Venezuelan viruses, which could affect Australian wildlife. CSIRO scientists have ruled out the use of viruses from Venezuela to control cane toads in Australia because laboratory trials show that the viruses can also kill native Australian frogs as well as the toads. At AAHL, a specialized group has been formed bringing together expertise in virology, aquatic animal pathology, electron microscopy, and molecular biology. Expertise in the group has resulted in the isolation of previously unknown disease causing agents in Queensland. The objective of the current project is to find exotic, infectious microbial agents which may spread throughout cane toad populations in Australia and decrease their numbers.

The project is also assessing the effects of these agents on adult, metamorphic, and juvenile life stages of the toad, since it is likely that different life stages have differing weaknesses. Further research is being undertaken by CSIRO. Giant toads are often transported in shipments of fruit and other commodities. Until effective control methods are available, quarantine checks and the destruction of any accidental releases of toads are essential to reduce their rate of spread. Challenge experiments have commenced to evaluate the effects of viruses on toads.

These experiments are conducted under maximum microbiological security to ensure that escape of the viruses cannot occur. Toads are maintained in laminar flow cabinets, within sealed rooms. The air pressure of the rooms is lower than atmospheric pressure; thus ensuring all air movement is into the room. Air leaving the room is double filtered to eliminate the smallest viral particle from escaping. Water from the room is heated to kill any infectious agents. Entrance to the room is through an air-lock and exit of personnel from the room requires a full three minute shower.

In association with the challenge experiments is a spectrum of microbiological, serological, and molecular studies to characterize and compare the agents under investigation, to establish information on the host’s resistance to infection, and to gather information related to similar agents in toads and other amphibian populations. Should an agent be found which offers the potential for control of the toad, an extensive series of subsequent studies is planned. To achieve the objectives of the project, amphibian populations from around the world are being studied for possible infectious agents. An international network of scientists, scientific institutions, interest groups and interested individuals is being developed for information exchange relating to diseases and population declines of amphibians. Potential for biological control of the toad is considered good, as the toad is the only representative of the bufonid family in Australia and is distinct from other Australian amphibian species. In addition, many species of the genus Bufo exist overseas, offering exciting prospects that an infectious or parasitic agent from these may cause disease in Australian Bufo marinus, without affecting native species.

It is hoped that these studies will provide valuable information on the causes of, and initiating factors behind, the recent declines in frog populations in Australia, Britain and elsewhere. Also, to contribute to the possibility that an infectious agent might be found that would control cane toads in Australia. They are constantly looking for possible pathogens for consideration for the biological control of cane toads. Finally, Chinese medicine manufacturers have been using the toads for centuries in the treatment of Cardio Vascular Diseases and Cancer treatment. It is highly likely that the cane toad will one day be farmed in Queensland for production of therapeutic medicines. Conclusion There is still much work to be done to fully understand what effects cane toads have on native wildlife, and just how far they can spread.

There are some reasons for optimism. In the areas where cane toads have been around for the longest time, their populations have declined after the initial population explosion. It is also possible that some native animals are learning to avoid eating them. Other animals have shown they can eat the toad. The Keelback Snake can detoxify the venom and Water Rats, Ibis, Crows and other birds turn the toads over and eat only the non-poisonous internal organs.

Opinion is divided concerning their current status, some think the native wildlife is starting to recognize them as a threat and they stay away. Australia is still a long way from controlling cane toad numbers or putting a stop to their expansion. Scientific evidence suggests that this imported animal represents a nuisance to man and an ecological threat to the Australian environment. The rapid growth of the species may have consequences in areas considered irrelevant at the time of its introduction. The cane toad has provided a painful lesson in what can happen to native species when an exotic species is introduced to a new habitat.



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