Over the past few years, there has been a LOT of publicity in the media about frog declines and, in particular, the role that disease has had in causing many species to decline and even disappear entirely. However, the overwhelming majority of attention thus far has been focused on the relatively recently discovered "chytrid fungus" (Batrachochytrium dendrobatidis for the scientifically inclined).
We sometimes answer our phone and the voice on the other end says, "I just found a frog with that chytrid fungus" but that is seldom what the problem is. Its just all the media publicity that makes people think there is only one disease out there so this frog they found HAS to have chytrid.
Cancer in amphibians is considered to be an extremely rare event. However, four cases were found by CSIRO several years ago during their chytrid testing of hundreds of frogs from eastern Australia. Not intending to outdo the rest of the country, Cairns has the dubious distinction of already having confirmed at least a dozen cases of squamous cell carcinoma (skin cancer) in local frogs (these are in addition to what CSIRO has found) and, more recently, at least one case of adenocarcinoma and a possibly world's first case of osteosarcoma in a frog.
In January 2003, we received three batches of really sick looking tadpoles, all of which died as tadpoles and some of which were sent to a lab. These were the last remaining tadpoles found in three different backyard ponds. They were grey in colour (the species is usually speckled brown), very sluggish and had pourly formed legs. We asked a virologist to have a look. With the condition they were in, not a lot of testing options were available but sequencing could be done and the result was that they had an unidentified virus. Since then, more virus tests have been performed and two herpes viruses appeared using PCR but little has been done since to progress through further required tiers of testing (no funds).
Amphibians, especially ground dwelling species, can come into direct contact with various bacteria and fungi constantly which will be living in the soil or water or present on the insects they eat. If the frog or toad is healthy, these "environmental" pathogens will not cause any problems. But when the animal is stressed or these pathogens build up in an enclosed environment (such as a keeper's tank in captivity), these bacteria and fungi can overwhelm the animal and cause infection.
In July 2002, something new and highly contagious arrived in the Cairns Frog Hospital. We suspected chytrid but it wasn't. We then obtained some positive results for Mucor amphibiorum but several hundred frogs came in with respiratory symptoms and M. amphibiorum does not have a respiratory component. Since it first arrived, we have received well over 1,500 frogs with the new disease (we bought a very expensive biological air filter to handle it!) and these have come from an area stretching from Gladstone to Thursday Island in the Torres Strait. We have had reports from other areas such as northern NSW and we've seen TV footage of Northern Territory frogs that looked suspicious but the animals have not yet been sent to Cairns for confirmation.
The majority of diseased frogs that the Cairns Frog Hospital received in its first five or six years were White-lipped tree frogs (Litoria infrafrenata). These large and long lived frogs were being attacked in a similar way. The scientific explanation for the existence of these factors was that these frogs were obviously without a functioning immune system. So what happened to it? Why would one or two species living in an area known to support dozens of species suddenly lose their immune system?