What is Chytridiomycosis

Chytridiomycosis is an infectious disease in amphibians, caused by the chytrid fungi Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans. This disease has been linked to dramatic population declines or even extinctions in amphibian species in various parts of the world.

Chytridiomycosis affects the keratin-containing layers of an amphibian’s skin, which in frogs can lead to a thickening of the skin. This is particularly harmful to amphibians because they partly respire through their skin, and the disease can therefore interfere with their ability to absorb water and electrolytes, leading to heart failure.


How it affected frogs in general

Chytridiomycosis has had a devastating effect on global frog populations. First discovered in the late 20th century, the disease has since been implicated in dramatic population declines or even extinctions in several species of frogs across the globe.

The disease is deadly to many species of frogs because it interferes with their ability to absorb water and electrolytes through their skin, which can lead to heart failure. Some species are more susceptible to the disease than others, and the impacts vary widely between regions and species.

In Central America, for instance, chytridiomycosis has been linked to the extinction of the golden toad and the harlequin frog. In Australia, it’s contributed significantly to the decline of the Corroboree frog and the sharp-snouted day frog. In the western United States, it’s played a part in the decline of the mountain yellow-legged frog.

It’s worth noting, however, that some species are more resistant to the disease and can carry it without showing symptoms, acting as reservoirs for the fungus. These carrier species can then transmit the disease to more susceptible species, contributing to its spread.

How has it affected the Mountain yellow-legged frog

Chytridiomycosis has had a profoundly negative effect on the mountain yellow-legged frog (MYLF) populations. This species, which includes two distinct subspecies – the southern mountain yellow-legged frog (Rana muscosa) and the northern mountain yellow-legged frog (Rana sierrae), resides in the high-elevation aquatic ecosystems of California’s Sierra Nevada mountains and the Transverse Ranges of Southern California.

Mountain yellow-legged frogs were once abundant in these regions. However, their populations have experienced a precipitous decline, with estimates suggesting a decrease of over 90% in their range. While several factors have contributed to this decline, including habitat degradation and introduced predatory species, chytridiomycosis has been identified as one of the primary drivers.

Bd infects the skin of amphibians, a vital organ through which many species, including the mountain yellow-legged frog, absorb water and breathe. The infection can disrupt these essential functions in susceptible species and lead to cardiac arrest. Since MYLFs live in cold water habitats that favour Bd’s survival and propagation, they are particularly vulnerable to infection.

Interestingly, laboratory experiments have shown that some MYLFs can clear the infection and survive if exposed to warmer temperatures outside the optimal temperature range for Bd. However, their high-altitude habitats do not naturally provide such conditions.

Conservation efforts have been initiated to mitigate the impact of chytridiomycosis on MYLFs. These include captive breeding programs, habitat restoration, and testing novel methods to manage the Bd fungus in the wild. But despite these efforts, the future of mountain yellow-legged frogs remains uncertain, and they are currently listed as endangered under the U.S. Endangered Species Act.

What can we do?

Reducing the impact of Chytridiomycosis, a disease that has caused the decline and extinction of many amphibian species worldwide, requires a multi-faceted approach. Here are a few strategies:

  1. Captive Breeding and Reintroduction: Affected species can be bred in captivity and reintroduced into the wild. The captive environment allows for careful monitoring and treatment of potential outbreaks, and individuals can be treated for the disease before reintroduction. However, this method requires significant resources and can be challenging due to the difficulties of maintaining genetic diversity.
  2. Environment Manipulation: Since the fungus thrives in cooler temperatures, manipulating the environment to increase temperatures can help reduce its impact. For instance, creating basking sites where amphibians can warm up may help them fight off infections.
  3. Bio-Augmentation: This involves introducing probiotic bacteria that can inhibit the Chytrid fungus. Some amphibians naturally have such bacteria on their skin, and experiments have shown that augmenting this bacterial community can help protect against the disease.
  4. Antifungal Treatments: Infected individuals can be treated with antifungal drugs, such as itraconazole. While this approach can be effective, it’s more suited to captive populations due to the difficulties in administering treatments in the wild.
  5. Vaccination: While a vaccine for Chytridiomycosis is currently not available, research is ongoing. If successful, it could provide an effective way to protect susceptible populations.
  6. Public Education and Biosecurity Measures: Educating the public about the dangers of moving amphibians between locations can help prevent the spread of the fungus. Similarly, biosecurity measures, like disinfecting footwear and equipment, can minimize the risk of introducing the fungus to uninfected areas.
  7. Habitat Protection and Restoration: Protecting and restoring the natural habitats of amphibians can help bolster their populations and increase their resilience to diseases like Chytridiomycosis.

Each of these methods has its own challenges and limitations, and none can completely eliminate the threat of Chytridiomycosis. However, by combining these strategies and adapting them based on ongoing research, it may be possible to reduce the disease’s impact and help safeguard the world’s amphibian populations.