Immunised frogs against the Chytrid fungus and the efficiency of frog saunas

In a recent breakthrough for amphibian conservation, Anthony Waddle (FFN Award winner 2025) and his team have released 500 immunised juvenile green and golden bell frogs in the Sydney Olympic Park to help them fight against the Chytrid fungus.

The Chytrid conundrum

Chytrid fungus (Batrachochytrium dendrobatidis) is a global crisis that causes a deadly infectious disease in amphibians. This fungal skin disease has been devastating for amphibians worldwide, wiping out entire populations and pushing around 90 species to extinction. One such species affected by Chytrid is the green and golden bell frog (Ranoidea aurea), one of the focus species of Anthony.

Immunisation as a tool against the Chytrid crisis

Like any other immunisation exercise, the basic idea is to help the green and golden bell frogs to develop immunity against this fungal infection. It is the process of recognising an infection, fighting it off, and remembering how to defend against it in the future.

The released individuals can defend themselves against the chytrid fungus in locations where this fungus is widespread. These individuals will also provide information whether immunising individuals before their release will provide them a fighting chance against the chytrid fungus. If all goes well, this immunisation will increase the survival rate of the frogs and allow for these healthier frogs to reproduce and repopulate.

Frog saunas and their effectiveness

Apart from the immunisation trials, sun-heated artificial hotspots, also known as ‘frog saunas’, remain a cost-effective interventions in the wild and their effectiveness was studied to see how environmental factors affect them.

In a recent study that Anthony has co-authored, a site in a cool semi-arid climate was compared with a site in a humid sub-tropical climate to understand the effect of external environmental conditions on the success of the frog saunas.

What’s the verdict?

The study set-up consisted of the frog saunas and wooden planks in two different locations with very different climatic conditions. The wooden planks mimic the natural shelters that are usually used by amphibians in the wild.  The frog saunas were warmer than the wooden planks in both the sites. The saunas in the sub-tropical climate recorded a high temperature (≥ 25˚C) for at least four hours per day. However, the saunas in the semi-arid climate recorded the 25˚C for only 30 minutes on average during the study. In short, the more sunlight the frog saunas receive, the more effective they become.

Implications for amphibian survival and Chytrid prevalence

The growth of the disease-causing Chytrid fungus increases in the temperatures between 10 ˚C and 25 ˚C and it decreases between 25 ˚C and 30 ˚C. The frog saunas in the sub-tropical climate achieve temperatures at which the growth of the fungus reduces, and it benefits the frogs causing a better outcome. However, the frog saunas in the cooler semi-arid climate achieve temperatures that favour the growth of the fungus and worsen the outcome for the frogs. This highlights the effects of climatic conditions especially solar exposure of the frog saunas for it to be effective in controlling this devastating disease.

Offsetting climatic disadvantages in the future

The study suggests some areas where future research can focus in order to make the frog saunas more advantageous in cooler climates. The researchers suggest actively heating up the shelters by incorporating solar panels. In other words, there is no one size fits all approach when it comes to these frog saunas. Thus, future research would need to concentrate on making the frog saunas more advantageous in all climatic conditions.

This research about the effect of climate and the immunisation of frogs reminds us that amphibian conservation is taking giant leaps in the hands of committed individuals. These 500 immunised frogs are hopeful leaps in the long journey of protecting our planet’s wildlife.