Getting the jump on frog disease!!

May 2001

Top: Great Barred Frog with Chytrids

Centre: Red-eyed Green Tree Frog

with a deformed eye

Bottom: Green Tree Frog with Chytrids

Photographs: Lee Berger

Disease and Declining FrogPopulationsThere is no doubt that frogs generateintense interest in the Wet Tropics.While residents and visitors to theregion gain great enjoyment fromliving in such close proximity to thesedelightful creatures, researchers,conservationists, veterinarians andmicro-biologists grow increasinglyconcerned for their immediate andlong-term future.

Such groups are acutely aware thatamphibian populations have beensteadily declining for more than adecade. Many species are now endan-gered, and some have disappearedcompletely. This disturbing trendapplies not only in the Wet Tropics, butis occurring on a global scale.

A number of theories have been putforward to explain the phenomenon,including: habitat destruction, acidrain, fertilisers and pesticides, globalwarming and ozone depletion, theintroduction of exotic predators anddisease. It is clear however, that no onesingle causal factor can be isolated.

In a bioregion like the Wet Tropics,where humans and amphibians live inrelatively close proximity and there isa high level of biodiversity amongfrogs, disease and the spread ofinfection among frog populations is aprime concern.

Amphibian Disease Conference 2000In order to address this particularissue, the Rainforest CRC organisedan International Conference in Cairnsin August 2000. A Workshop whichfollowed was designed to developstrategies to lessen the impacts ofknown and emerging pathogens onwild amphibian populations. Special-ists from the U.K., U.S.A., Spain, NewZealand, Germany, Uruguay, and

Australia converged to consideroptions for effective control and man-agement, and to devise strategies tominimise the risks of disease on wildamphibians at global, national,regional and local community levels.Delegates included policy-makers,laboratory and field scientists,veterinarians, commercial frog aqua-culturalists,micro-biologists,repre-sentatives from frog interest groups,horticultural industries and thegeneral public. The objectives of theconference were to:• assemble experts with the most

current information on amphibianpathogens and their effects, and

• promote and improve net-working, information flow andexchange of ideas among peopleworking on and with amphibiandisease.

The aim of the Workshop was todevelop a set of recommendations forgovernment bodies, non-governmentorganisations and individuals, whichoutlined actions that would lessen therisks of disease to wild amphibianpopulations.

Which diseases cause the greatestconcern?Infectious diseases capable of causingdeclines of wild amphibians:• are highly virulent• affect more than one species• affect the adult form only• are associated with water, and• persist once frogs have disap-

peared either in another host or inthe environment itself.

During the Conference, two infectiousagents fitting this profile were identi-fied as being of greatest concern inrelation to wild frog populations,particularly in Australia. These agentswere the Chytridi fungus andRanaviruses.

CHYTRIDIOMYCOSIS(The Frog Chytrid)This disease is caused by the fungusBatrachochytrium dendrobatidus and iswidespread in Australian frogs, canetoads and axolotyls. The spores of thefungus grow inside the outer layers ofskin, resulting in a thickening of theepidermis and keratin. This pathogenis capable of causing high incidence ofsickness and death in captivepopulations, and spores of the fungusare transmitted via water.

Obvious symptoms include:

• Abnormal posture - hind legs heldout from flanks, animal does notright itself

• Abnormal behaviour - nocturnalanimals in daylight, animal fails toflee or has seizure when handled

• Thickened epidermis, ulcerationson the skin and body swelling

• Death

Tadpoles do not display these symp-toms, but carry the disease in theirmouths when, during metamorphsis,the spores become redistributed to theskin of the body. This aspect is a greatcontributor to the spread of thedisease.

RANAVIRUSESRanaviral disease in amphibians iscaused by multiple species of closelyrelated viruses of the Ranavirus genus.Some Ranaviral species can infect am-phibians, reptiles and fish, but as yetthere have been no documented epi-demics in Australia. More obvioussymptoms of raniviral disease inamphibians include:

Tadpoles: decreased activity, pinprickbleeding (focal haemorrhages), bloat(ascites) and deathMetamorphs: decreased activity, fluidbuildup under the skin (anasarca), bloat(ascites) pinprick bleeding (focal haem-orrhages) and deathAdults: decreased activity, ulcerationsof the skin, pinprick bleeding (focalhaemorrhages) and death.

Strategies emerging from WorkshopStrategies which the Workshop iden-tified to lessen the risks and control theimpacts of disease included:

• Prevention of import of infectedanimals into disease free areas

• Limiting movement of all frogsbetween contaminated areas

• Implement protocols on handlingwild amphibians

• Maintaining healthy frogenvironments

• Collection and preservation ofgenetic material

Within the Draft Recommendationsproposals have been written to addressthe following issues:• Movement of amphibians in farm

produce - reduction at source andmanagement at receiving end

• Movement of amphibians in othermaterials like soil and water

• Dealing with pathogens in thelaboratory

• Decreasing the risk of disease inamphibian husbandry

• Reducing the spread of infectionduring field research

Community involvement imperativeThe draft includes several suggestionsthat are designed to make the most ofcommunity interest and involvement,and to encourage and assist furthercommunity participation in:

• Disease surveillance - monitoringmortality levels, and collectingroad kill samples

• Caring and nurturing - rehabilita-tion of frogs, repatriation, hus-bandry

• Population monitoring - densities,movements, reproductive activityand success

• Maintaining healthy amphibianhabitats - protection, creation, en-vironmentally friendly practices,surveillance for exotic amphibians

• Education - schools, public eventsand venues

• Support - moral, financial andpolitical

• Promotion - media and otherconservation groups

The complete draft recommendations

are available on the web at:

www.jcu.edu.au/school/phtm/

PHTM/frogs/adrec.htm