Immuno-deficiency complex - probably a virus
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:
1
Most were losing all their body weight
2
Most had large numbers of spirometra tapeworms under the skin or protruding from ulcers
3
Most were suffering from skin degenerative problems
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Most had at least 3 to 5 different things wrong with them simultaneously
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?
We of course became highly suspicious that a virus was possibly involved in the White-lipped situation:
1
The 'Mystery Pathogen' that we have been experiencing is only attacking two species of frogs - there are over 25 species present in Cairns alone and the pathogen has only shown up in Litoria infrafrenata (White-lipped tree frog) and Litoria caerulea (Common Green/White's tree frog). If an environmental pollutant was responsible - such as dioxin which is known to cause wasting problems - more species would be overcome.
2
Only adult frogs are being affected which is a common feature of the wasting syndromes being caused by prions (a subvirus) overseas such as Chronic Wasting Disease in the US and Canada. CWD only affects deer and elk and is being very closely watched by the US Fish and Wildlife Service.
3
The immune system of these frogs is being disabled by the pathogen and some viruses have already been shown to cause disfunction of the immune system such as human AIDS, Feline Immunodeficiency Virus (also sometimes referred to as cat AIDS) and ranaviruses.
4
Coincidentally, all the Litoria infrafrenata that have contracted the wasting syndrome are also carrying large numbers of the tapeworm Spirometra erinacei which only breeds in cats. Additionally, Australia has the second highest rates of Feline Immunodeficiency Virus in the world and the virus is most often found in feral cats and others which are domestic but free-ranging. FIV also takes up to five years to cause illness which could provide an alternate explanation as to why we are seeing only mature frogs affected and in two species which are known to live to ten years or more in the wild.
5
Continuing the line of enquiry along the potential cat connection, so far, all the affected frogs we have received with the condition have come from areas where human residential settlements are located. (We have applied for funding to survey in remote areas but have been unsuccesful so far.)
6
Aside from the frogs with obvious parasite problems and the wasting syndrome, we have also received what would be considered an excessive number of skin cancer cases (cancer in lower animals is extremely rare and has only occasionally been documented in amphibians). At first glance, these frogs with large facial tumours might be dismissed as being yet another victim of our intense tropical sun but this is not the case. The particular cancer involved in most of the tumour cases we have seen in Cairns is called nasopharyngeal squamous cell carcinoma and this cancer is actually very common in China. However, it hasn't been documented in frogs there - it's a cancer of humans - and it's caused by a virus! Additionally, we are receiving a growing number of tumour cases which have been biopsied and identified as "epidermal papillomas" and these are commonly recognised to be caused by a papilloma virus. ALL the tumour cases (except one melanoma) have been in the White-lipped which might imply that two viruses are working together to cause the cancer to activate only in this species.
7
Hundreds of people have turned in frogs to us or provided information by phone after media stories and they remarkably report exactly the same story, almost word for word: that they had heaps of frogs in their yards until 1997/98 when they simply disappeared or were found dead. Since then, they have only had a few occasional visiting frogs and, during the 2001 and 2002 winters, even these were found dead one after the other. This would be consistent with the arrival of a new emerging disease.
8
One of the secondary conditions that we are seeing (again) only in the White-lipped tree frog (Litoria infrafrenata) is caused by excessive bile in the body. A researcher investigating a mysterious disease killing skinks in one region of South Australia came upon a new blood disease where red blood cells were being destroyed by a bile containing chemical called biliverdin. He believes that this disease is being caused by a virus and an unidentified virus was found in some of the his reptile specimens. Our frogs with the excessive bile were examined by the same Perth researcher but the work was never concluded because the researcher migrated overseas. It is common for viruses to interact and for a virus to only cause disease when another specific virus enters the body. Because we have only seen this bile condition so far on the White-lipped, this species-specific situation provides more support to a virus rather than an environmental pollutant.
9
We have had some investigation by a UQ researcher into the possibility that the immune deficiency in the White-lipped might be caused by a retrovirus. The correct primers are essential in identifying not only the specific virus but the specific virus IN a specific target. We're not sure if there might have been technical issues with the UQ persuit of a mutated retrovirus - it was experimental work - but the results were blank for a retrovirus. There is one more virus group which causes immune deficiency ....
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Ranaviruses (iridovirus) are active in Australia but it has been our observation that they are generally ignored by the establishment. There is a professor at James Cook University in Townsville with a very strong interest in this virus group and who has done a lot of testing over the years. He has had positive results for ranaviruses over many areas including Cairns but there is little funding available to continue this work. Considering the conservation impact of viruses with their long dormancy periods, we are very curious as to why this virus group tends to be "shown the door" so often by the powers that be!
