In 1993 Keith McDonald of the Queensland Department of Environment and
Heritage asked Rick Speare of James Cook University to help investigate
the role of disease in the disappearance of upland frogs in Queensland.
Keith, a renowned frog ecologist and taxonomist, had been monitoring frog
populations since the late 1970s. He had followed the disappearance of
frog populations in upland sites from the original crashes in the
D'Aguilar and Conondale ranges through central Queensland into the wet
tropics. In 1993 one upland population of frogs remained unaffected in
the wet tropics on Big Tableland, near Cooktown. In particular this was
the last known habitat of the sharp snouted day frog, Taudactylus
acutirostris, a frog only found above 400 m altitude.
Keith had realised that monitoring frog numbers allowed declines to be detected, but had not provided anwers about what was the cause. Monitoring pesticides, heavy metals, and water quality had also shown that pollution was not involved in these pristine sites.
Rick Speare, although now working in human public health, had spent the years from 1988-1990 investigating disease in the cane toad, Bufo marinus. With funding from the Wet Tropics Management Authority Rick joined Keith and his team in monitoring the frogs on O'Keefe Creek, Big Tableland. Soon after, mortality occurred. Adults along the study site were found ill or dead. During a trip in November 1993 T. acutirostris numbers appeared still to be adequate, but ill Litoria nannotis and Litoria rheocola were found. A group of T. acutirostris were collected to be maintained in captivity at James Cook University, Melbourne Zoo, and Taronga Zoo. Within 3 months of this initial episode all adults of T. acutirostris, L. nannotis, L. rheocola were gone from O'Keefe Creek above 400 m. Tadpoles of some species survived, but no establishment by metamorphs were detected. Numbers of Litoria genimaculata declined at the same time, but the population recovered to pre-crash levels after 2 years.
Although this was a disaster for the frog populations, it was a wonderful pathological opportunity since it was the first time ill and non-autolysed dead frogs were available for pathological examination. A disease team headed by Rick Speare, and including Kelly Field and Joy Koehler, investigated the specimens. They were quickly able to rule out bacterial septicaemia as a cause; aeromonads had been postulated as agents in ecological work overseas. However, the pathology was unspectacular and indicative of a toxic or peracute viral cause. Viral isolations were unsuccessful. Early immunoperoxidase tests on histological sections for ranavirus were positive, but could not be confirmed. The early report concluded that the frogs had not died of bacterial septicaemia, and an unknown virus or toxin may be the cause. Not the penetrating insights wanted!
Ron Slocombe, a veterinary pathologist working for the Melbourne Zoo, made an interesting observation early in 1994. All the T. acutirostris sent to the zoo had died in spite of intensive and highly skilled husbandry. Even metamorphs emerging from tadpoles died within a month of emergence. The only consistent lesions found in the frogs Ron looked at were heavy infections of the epidermis with a microscopic organism, that looked like a protozoa or microspora. Undescribed, of course!
Rick Speare had also noted these organisms occasionally in the skin of the Big Tableland frogs and more commonly in the T. acutirostris that had died in husbandry at JCU. At this stage, however, he dismissed them as being minor parasites unrelated to the deaths in the wild.
Rick and the Queensland Frog Recovery team decided a full time vet pathologist was needed to continue investigations into the cause of death of these frogs, and so funding was obtained from the Australian Nature Conservation Agency for a PhD stipend. Lee Berger, a veterinarian with an interest in wildlife, began work in 1995 at the CSIRO Australian Animal Health Laboratory to study disease in Australian frogs under the supervision of Rick Speare and Alex Hyatt. Alex and Rick had worked together previously on the Bohle ranavirus from north Queensland. Alex was also conducting experimental work on ranaviruses and Bufo marinus, and had experience in amphibian diseases. The combination was remarkable; AAHL with its world class expertise in the laboratory investigation of unknown viral agents, Rick Speare with expertise in field and lab investigation of infectious diseases of unknown causes in many species of animals, Keith McDonald with his extensive knowledge of Queensland frog populations, and Lee Berger with her tenacity and persistence.
As little was known about diseases in any Australian frogs, the group decided to investigate disease in both declining and non-declining populations. A multidisciplinary network was set up involving herpetologists in universities and government departments. Sick frogs were collected from all over Australia and forwarded to the amphibian disease group for diagnostic tests. The team also recruited people with expertise in specialty areas, e.g., parasitology and molecular biology, who were keen to donate their time, and contacted groups around the world working on amphibian disease in order to share information. The approach adopted was that collaboration and open information exchange would allow us to progress much more rapidly.
After much detailed work looking further for the mythical virus in the Big Tableland and other frogs, Lee Berger decided that the only possible agent was the "minor" skin parasite detected in both wild and captive frogs. In an experiment Lee demonstrated that this agent, the amphibian chytrid, was indeed a primary pathogen. From the ultrastructure of the zoospore Peter Daszak identified the agent as a new species in a new genus. Further weight was given to this by Louise Goggin's molecular biological work which placed the organism most closely to Chytridium confervae.
We have provided on this web site some of our protocols that were devised to facilitate the functioning of the network, such as the instruction sheet on how to collect and submit specimens for pathology. We hope that others beginning similar studies will find them useful and will adapt them for their own use.
The Australian frog recovery effort has been well coordinated for a number of years. As amphibian pathologists have been involved in the recovery effort since 1993, Australia has led the world in disease investigations into declining populations. We had been investigating the role of chytrid fungi in mass mortalities, and had determined it caused 100% mortality in experimental trials when it was discovered in a mass mortality event in Panama. We have now published the first evidence for a chytrid as a threatening force in collaboration with the US researchers, David Green and Karen Lips, working in Panama, - " Chytridiomycosis causes amphibian mortality associated with population declines in the rainforests of Australia and Panama" by L. Berger, R. Speare, P. Daszak. DE Green et al, in Proceedings of The National Academy of Sciences 1998; 95: 9031-9036. This is a remarkable publication from the collaborative perspective - 14 authors from 3 continents and 11 institutions!
Independent of our group the chytrid was identified as a cause of mortality in frogs at the Washington Zoo by a group consisting of Don Nichols, Alan Pessier and Joyce Longcore. Don had seen the chytrid in the skin of frogs at the zoo since 1991, and had established its identity working with Joyce Longcore, an expert on the Chytridales. To have two groups independently arrive at the same conclusion namely that the agent caused death of amphibians, and that the agent was an undescribed member of the Chytridales, increased the confidence in the conclusion.
The current work is funded by Environment Australia under the endangered species program. We have found that the amphibian chytrid is widespread in eastern and southern Australia and is also in Perth. Lee Berger and the team have found the chytrid in 23 species of amphibians in Australia including 7 threatened species of frogs.
Much remains to be done. In particular, we need to know how the amphibian chytrid fungus and host interact with the environment to explain why highly susceptible frog species that extend the length of water bodies die in locations above 400 m, but survive below this altitude.
Frog disease research is an excellent example of the benefits of global collaboration. Groups in Australia, UK and USA work together. Go to the file that lists their names. Each person contributes in their own field, and information is shared freely for the benefit of all.
In Australia one of our goals is to strengthen the frog disease network by:
Updated 14 January 1999
by
Rick Speare