Recently published in the journal Transboundary and Emerging Diseases, a multinational study has developed a method to detect all known strains of this disease, caused by the amphibian chytrid fungus. This breakthrough will advance our ability to detect and research this disease, working towards a widely available cure.
What is the News?
For the past 40 years, a devastating fungal disease, called chytridiomycosis or chytrid, has been ravaging frog populations around the world. This is a “panzootic” – a pandemic in the animal world.
What is chytridiomycosis or chytrid?
The single-celled fungus enters a skin cell, multiplies, and then breaks back out onto the surface of the animal. This affects their ability to balance water and salt levels, and eventually leading to death if infection levels are high enough.
The high mortality rate and the high number of species affected make chytrid unequivocally the deadliest animal disease known to date.
Origin: Chytrid originated in Asia and spread to other continents through global travel and trade in amphibians.
The intensity of the disease: Chytrid has been devastating frog populations for the past 40 years, wiping out 90 species, including seven in Australia, and causing severe declines in over 500 frog species.
The disease overwhelmed many species’ immune systems, leaving them unequipped to defend against it, resulting in mass mortalities.
Note: In the 1980s, amphibian biologists began to notice sharp population declines. Only in 1998, the chytrid fungal pathogen was finally recognized.
Diagnosis of Disease: Researchers use a quantitative polymerase chain reaction (qPCR) test to detect chytrid in frogs by swabbing their skin.
Note: The qPCR is a way to measure the volume of DNA from a species of interest.
Recently, Indian scientists have verified the qPCR test and reliably detects chytrid. This new qPCR test can detect strains of chytrid from Asia and another closely related species of chytrid that infects salamanders.
Immunity: So far, there is no clear trend between resistance and immune function.
Research in Asia: Asia is lagging behind the rest of the world in chytrid research.
The most puzzling thing about chytrid is that some amphibian species – even those that have not evolved with the pathogen – don’t become sick when they carry the fungus. These species have some form of natural immune resistance.
However, frog immunity is extremely complex. Immunity might come from anti-microbial chemicals within the skin, symbiotic bacteria on the skin, white blood cells and antibodies in the blood, or combinations of these mechanisms.
So far, no clear trend has been found between resistance and immune function. To make matters more complicated, there is also evidence chytrid can suppress a host’s immune response.
Because there haven’t been any observed chytrid declines in Asia, and because detecting chytrid in Asia has been difficult, Asia is lagging behind the rest of the world in chytrid research. Yet the new qPCR test detected high levels of chytrid in a range of amphibian species across India. Having the ability to study chytrid in its region of origin may help us understand how Asian species evolved resistance – research that may hold a key to help researchers develop a cure for those species in Australia, North and South America, and Europe that are now on the brink.
While the new qPCR test was successful at detecting chytrid in samples from India, Australia, and Panama, we will need to validate and promote the method so it becomes the new gold standard for chytrid testing. Future work will involve using the test to analyse samples from Europe, and samples from Brazil where genetic studies show that chytrid has diverged.
In time, this new way to detect chytrid could be the first step in helping to save frogs – the hidden gems of our forests and wetlands.
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animal disease, animal disease