Recently, the laboratory has been commissioned and funded to undertake research into the feasibility of biological control of the cane toad, Bufo marinus, using viruses or other microbial agents found overseas.
Bufo marinus, the cane toad, was intentionally introduced into coastal Queensland in 1935 in an attempt to control cane beetles. Since that time, the toad has spread in a westerly and southerly direction. It is now found throughout Queensland and has made significant incursions into the Northern Territory and New South Wales. The major concerns about the toad involve its prodigious appetite, and the toxicity of all of its life stages to endemic fauna. 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 now almost certainly establish itself throughout the environmentally sensitive and biologically and commercially important rivers and 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 thus whether a biological control agent is required. The funding also encompasses the search for and assessment of possible control agents.
Funding of the present 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, with the isolation of a number of viral and bacterial agents for investigation at AAHL.
At AAHL, a specialised and unique group has been formed bringing together expertise in virology, aquatic animal pathology, electron microscopy and molecular biology. The group consists of Alex Hyatt, John Humphrey and Jacques Zupanovic, with technical support. Expertise in the group has resulted in the isolation and/or characterisation of previously unknown disease causing agents including Bohle-virus (BIV) from the ornate burrowing frog Limnodynastes ornatus from Queensland.
The objective of the current project is to find exotic, infectious microbial agents which may spread throughout cane toad populations in Australia and which may compromise the host by causing disease and deaths, or by more subtle effects, for example by reducing immune function and the capability to resist other infections, or by reducing reproductive capacity. The project is assessing effects of exotic agents on adult, metamorph and juvenile life stages of the toad, as it is likely that different life stages have differing susceptibilities.
Potential for biological control of the toad is considered to be good, as the toad is the only representative of the bufonid family in Australia and is thus taxonomically distinct from Australian amphibian species. In addition, many species of the genus Bufo exist overseas, offering exciting prospects that an infectious and/or parasitic agent from these may cause disease in Australian Bufo marinus, without affecting native species.
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 hermetically sealed rooms. The air pressure of the rooms is lower than atmospheric pressure, thus ensuring that all air movement is into the room. Air leaving the room is double filtered to exclude the smallest viral particle from escaping. Water from the room is heated for a prolonged time to inactivate infectious agents. Entrance to the rooms 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 characterise and compare the agents under investigation, to establish information on the host response and resistance to infection, and to gather epidemiological information related to the occurrence of the 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 which will involve challenge of indigenous amphibia and fish species to ensure that the agent does not harm indigenous aquatic animals.
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.
In addition to the search for potential microbial pathogens for the biological control of cane toads, AAHL is collaborating with James Cook University of North Queensland (under separate funding) to investigate causes of declining rainforest frog populations in tropical Australia. Preliminary evidence strongly suggests that a virus plays a role in such declines. Hence an MSc student has recently been appointed to undertake investigations into the significance of viruses in frog populations. This project, jointly undertaken at AAHL and James Cook University, complements and enhances the biological control project. AAHL is also about to commence collaborative studies with British scientists to characterise virus isolates from British frogs which are believed to be responsible for alarming deaths in frogs in recent years. It is intended to compare these viruses with viruses from elsewhere, including Australia, and to establish whether or not they cause disease in cane toads.
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 and will contribute to the possibility that an infectious agent might be found that will control cane toads in Australia. We are on the continual look-out for possible pathogens for consideration for the biological control of cane toads. If anyone has observed dead and/or dying toads or other amphibian species then they can contact us on the numbers listed below.