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What is chytridiomycosis?

Chytridiomycosis is another major threat for amphibians at national and world. A global effort to understand amphibian population decline, carried out by a group of men and women scientists, and made up of Professor Andrew Cunningham (scientific advisor to the NGO Ranita de Darwin), managed to discover at the end of the 1990s this emerging infectious disease of amphibian skin produced by the chytrid fungus: Batrachochytrium dendrobatidis(Bd).

Chytridiomycosis is frequently considered as one of the worst infectious diseases (diseases caused by microorganisms such as viruses, fungi and bacteria) that have affected any species of animal in the planet Earth.

Click to view to see the chytrid fungus by microscopy.

Chytridiomycosis in amphibians is considered one of the infectious diseases with the greatest negative impact, since there are a large number of species affected (has been associated with the decline of 501 amphibian species) and because it has the ability of produce extinction of a large number of species, being associated with the presumed extinction of 90 amphibian species worldwide. In this way, this disease has become one of the major global threats for amphibian conservation.

mapa presencia quitridiomicosis

Olson et al. (2021)

Infectious diseases such as chytridiomycosis can be study scientifically retrospectively, this means looking back, using animals stored in museums.These types of samples play a fundamental role in these studies, and are one of the many justifications for keeping animal samples in museums.

In the case of Darwin's Frog and his sister, the Cowboy Toad (Rhinoderma rufum), numerous specimens are kept in museums in Chile, North America and Europe.
From these samples it was possible to demonstrate, in a study led by the scientist and academic Claudio Azat, that the first infections with the fungus that causes chytridiomycosis appeared in both species of frogs in Chile during the 1970s, coinciding with the enigmatic disappearance of the Toad Vaquero.

We now have evidence that the variety of chytrid fungus present in Chile is genetically identical to fungi present in Europe and various parts of the world; the analysis of its genome suggests a recent introduction of this variety to our country, probably caused by the global trade in live amphibians or other aquatic animals for laboratory use, as pets or food (for example, the African Frog).

ranas africanas

African Frog - Photography by Claudio Azat

Also we have monitored a large number of wild populations of Darwin's Frog, which has indicated that chytridiomycosis is present mainly in northern populations (roughly between Biobío Region and Los Ríos Region), this being also the area where the Darwin's Frog has decreased most dramatically during the last three or four decades.

Click to see the short documentary: 'Chytridiomycosis in Darwin's Endangered Frogs'.

In Darwin's Frog, the Chytridiomycosis produces a high mortality in infected individuals (almost 100%), but not capable of producing epidemics or mass mortality. In contrast, the cases of the disease occur in low numbers, but distributed throughout the year.Unfortunately, this negative effect seems to have the capacity to produce the decline and extinction of populations of the species.This is a new paradigm in the study of infectious diseases of wild animals, which tells us that, even when we do not see obvious negative effects of an infectious disease in nature (for example, mass mortalities), infectious diseases can still represent a risk that threatens the survival of wild populations.

A hopeful discovery emerged thanks to data from the long-term monitoring of Darwin's frog populations that NGO Ranita de Darwin has been carrying out since 2014. We have observed that some populations have the ability to counteract the high mortality caused by chytridiomycosis through a increase in the reproduction of individuals, which would lead to a greater number of juveniles are born year after year in these populations. However, apparently not all populations of this species would have this ability to compensate for the negative effects of this disease; populations that are unable to counteract the negative effects of the disease are more likely to become locally extinct.

resultados estudio captura recaptura ranitas de darwin

This study highlights the importance of variation between populations in life history strategies about him fate of host populations after the onset of infectious diseases. Furthermore, one of our results suggests that an increase in reproductive effort may be one of the processes underlying the compensatory recruitment in populations of amphibians susceptible to the chytrid fungus.

Who should be more vigilant in preventing chytridiomycosis?

• Professionals working with amphibians (zoos, researchers, environmental consultants).

• Students.

• Groups and societies dedicated to the conservation of wild fauna.

• People who encounter frogs casually or non-casually.

Prevention actions

It is recommended that parks and other natural areas have disinfection area (covered footbaths). When traveling from one site to another, it is recommended that the following hygiene precautions be taken to minimize the possibility of disease transmission:

Personal hygiene:clean areas of the body that may have been in contact with the ground, mud, leaves, mosses (hands, arms, knees, etc.) with a disinfectant
appropriate. It is preferable to do this before entering the vehicle or moving to another location.

Footwear and clothing:footwear should be cleaned and disinfected at the start of fieldwork and between each sampling site. This can be accomplished by initially scraping the boots to remove mud and immersing the soles in a disinfectant solution. The rest of the boot should be rinsed or sprayed with a sanitising solution. Clothing that has significant contact with frogs and the environment should also be changed or cleaned.

Prevent Disinfectants enter any body of water and use biodegradable disinfectants whenever possible. Several bagged changes of shoes/clothes between sites could be a practical alternative to on-site cleaning. On high-value sites, it may be desirable to store equipment and clothing at the entrance (for example, in a safe deposit box).

Equipment:equipment such as nets, scales, calipers, bags, scalpels, headlamps, flashlights, wetsuits and boots, etc. that are used at one site must be cleaned and disinfected before being used again at another site. Disposable items should be used whenever practical/possible. Non-disposable equipment should be used only once and disinfected later.

Vehicles:If it is suspected that mud and water on wheels and tires could be transferred to other bodies of water or amphibian sites, then these components should be cleaned and disinfected. This is particularly important when vehicles are used in areas not normally frequented by other vehicles. Disinfection must be carried out at a safe distance from bodies of water to minimize the risk of contamination.

Click to watch the National Geographic infographic video: 'The chytrid fungus: a threat to amphibians'.

To download the E-book Darwin's Frog and other incredible Chilean amphibians, click here

To download the book Darwin's Frog Conservation Strategy,click here

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