Global pandemics – why the amphibian extinction crisis also needs attention

GLOBAL PANDEMICS – WHY THE AMPHIBIAN EXTINCTION CRISIS ALSO NEEDS ATTENTION

Dr Jeanne Tarrant, Manager, EWT Threatened Amphibian Programme
JeanneT@ewt.org.za
Within the space of a month we have all become very familiar with terms associated with disease – epidemiology, infection rate, pathogen, asymptomatic, zoonotic, and so on. ‘Corona’ and ‘COVID-19’ have become household names across the world in a matter of weeks, as a virus invisible to the eye has brought life as we know it to a grinding halt across 210 countries and locking down nearly half the world’s population.

But did you know that frogs have been facing an even worse pandemic for the last twenty years? The chytrid fungus has caused death and species extinction at a global scale. Amphibians by their nature (they use both land and water during their lifecycles and have permeable skins) are very sensitive to changes in the environment. They are the most threatened animals on the planet with currently 41% of 8,000 known species at risk of extinction, largely as a result of loss of habitat, pollution, invasive species, and climate change. But disease is also a significant threat driving declines and extinctions of this group of animals.

In the late 1990s, researchers discovered that a fungal pathogen (Batrachochytrium dendrobatidis, or Bd for short) was responsible for the declines observed in frog populations since the 80s, including in remote areas otherwise not threatened by habitat destruction. Much research has been undertaken to better understand this pathogen, which causes a disease called chytridiomycosis, shortened to chytrid. Chytrid has been declared a notifiable disease according to the World Organisation for Animal Health. The disease threatens more species than any other disease known to science and it is the first wildlife disease known to cause widespread extinction. Recent research shows that it has, or is, causing declines in at least 501 species, with about 90 of these having gone extinct in recent decades. The chytridiomycosis panzootic represents the greatest recorded loss of biodiversity attributable to a disease, largely because of its ability to infect a wide range of hosts.

Chytrid fungus is an aquatic pathogen that causes skin damage in frogs, leading to electrolyte imbalance and cardiac arrest. It spreads through water, from host to host, and can persist without a host for weeks. Its very low host-specificity means it can easily move from one frog species to another, and it has now evolved to also infect salamanders. Chytrid is present in over 60 countries, with the worst affected regions being Australia, and South and Central America.

Just as we are seeing with COVID-19, the rapid spread of disease is a real hazard in our interconnected world. Amphibian chytrid fungus has been spread by globalisation and wildlife trade – particularly the pet and food trade – both legal and illegal. Sound familiar? Transporting and keeping frogs in suboptimal conditions increases their susceptibility to disease and disease transmission is elevated as a result of crowded conditions. The disease is also spread when infected animals escape and shipping materials are incorrectly disposed of. COVID-19 crossed to humans precisely because of the same reasons – inadequate health, sanitation and protection measures in wildlife trade and consumption.

While the amphibian pandemic may not have garnered much attention, there are many parallels between chytrid and COVID-19 that should cause alarm. The emergence of a pandemic that threatens human health has long been predicted by experts, and similar diseases will continue to emerge as long as humans continue to destroy wildlife habitats and harvest wild species for consumption. As we approach nine billion people on the planet, the demand for food, and the space to create it, grows. The opportunities for disease-causing pathogens to pass from wild and domestic animals to people, and vice versa, have never been greater. The consequences of this are now very apparent as healthcare systems become overwhelmed and the world economy faces potential depression.

So, what can we learn from both COVID-19 and chytrid? Not only do we require much stronger regulations on the movement and trade of wild species, but how we treat wildlife and wild spaces also needs more attention and should come from a place of respect. Protecting natural spaces is now more important than ever as we recognise the value of intact nature as a critical step to protecting human health, as well as stemming the massive loss of biodiversity we are currently experiencing. Part of the longer-term response to global diseases needs to include prevention of habitat loss. We can all play a part in this through our everyday consumer and family-size choices and having an empathy towards the other creatures we are still fortunate enough to share this, our only planet, with.