Testing breakthrough challenges ‘world’s worst wildlife disease’

Subject : Science and technology

Section: Health

Concept :

For the past 40 years, a devastating fungal disease has been ravaging frog populations around the world, wiping out 90 species. A a multinational study has now developed a method to detect all known strains of this disease, caused by the amphibian chytrid fungus.

The Panzootic

Unlike the global COVID-19 pandemic, you may not even be aware of this “panzootic” – a pandemic in the animal world. Yet it’s the world’s worst wildlife disease.
A panzootic is an epizootic (an outbreak of an infectious disease of animals) that spreads across a large region (for example a continent), or even worldwide. The equivalent in human populations is called a pandemic.
A panzootic can start when three conditions have been met:
- the emergence of a disease new to the population.
- the agent infects a species and causes serious illness.
- the agent spreads easily and sustainably among animals.

Chytridiomycosis: The deadly frog disease

Chytridiomycosis, also known as chytrid, is a fungal disease that has been decimating frog populations worldwide for the past 40 years.
The disease has caused severe declines in over 500 frog species and led to 90 extinctions, making it the deadliest animal disease known.

How does it infect?

Chytrid infects frogs by reproducing in their skin, damaging their ability to balance water and salt levels.
The disease originated in Asia and spread globally through amphibian trade and travel.

An extreme mortality rate

The extreme rate of mortality, and the high number of species affected, makes chytrid unequivocallythe deadliest animal disease known to date.
The single-celled fungus enters a skin cell, multiplies, then breaks back out onto the surface of the animal.
This damage to the skin affects the frog’s ability to balance water and salt levels, and eventually leads to death if infection levels are high enough.
It’s believed that global travel and trade in amphibians led to the disease being unwittingly spread to other continents like Asia.

Natural immunity

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.
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.