In the 1990s and 2000s, the raspy hum of many Central American rainforests died down.
An amphibian-killing fungus – Batrachochytrium dendrobatidis (Bd) – swept across the region, and ultimately the globe, drowning out the ribbits and croaks of millions and millions of frogs, toads and salamanders in what may be the greatest loss of biodiversity on record from a single disease. This fungal pandemic has harmed more than 500 species of amphibians, leading to the extinction of dozens more.
This colossal loss reverberated beyond amphibians and had a startling impact on human health. In Panama and Costa Rica, malaria cases quintupled as Bd wiped out mosquito-eating frogs, toads and salamanders, according to a study published this week in Environmental Research Letters. “The study found that around half to two-thirds of this increase in malaria cases was linked to amphibian declines – drawing one of the clearest lines to date between biodiversity and public health.”
Grid spoke with Karen Lips, a tropical ecologist at the University of Maryland at College Park and co-author of the new study about her findings and why we should view the extinction and biodiversity crises as a public health crisis. .
This interview has been edited for length and clarity.
Grid: I imagine a lot of people wouldn’t necessarily think of biodiversity as being related to public health. Why are they wrong and what led you to research a link between amphibian loss and malaria?
Karen Lips: I think that’s the core issue of the biodiversity crisis. We kind of made it a matter of saving panda bears and other charismatic beautiful things. But the reality is that biodiversity is the foundation of life on the planet, including us.
When we were studying the amphibian extinction crisis, we were really interested to see if there was a way to tie this to a direct impact on humans. The loss seemed like such a huge thing. We thought there must be a connection, but weren’t sure what it could be at first. We finally found this correlation between changes in frogs and changes in malaria.
G: The chytrid fungus caused this massive amphibian decline. Can you tell me a bit about what it is and why it had such an impact?
KL: Chytrid fungi are small, microscopic aquatic organisms that probably originated in Asia, but we have introduced them all over the world, probably through the pet trade. And where they’ve been introduced, they’re alien species, and the native species don’t really have a defense against them.
Chytrid fungi can infect just about every species of frog on the planet, over 1,000 species. It can basically kill them by giving them a very serious skin infection that prevents the frog or salamander from getting enough oxygen and getting enough water, which they do through their skin. And so they die.
The impact has been enormous. It’s been on all the continents of the world [except Antarctica], and caused a 70-80% decline in the number of frogs and salamanders. So you go from thousands and thousands of frogs in a pond to, like, two, and we’re seeing species go extinct all over the world. everything happened quite quickly.
G: Why did you think this loss of amphibians might impact human health?
KL: I had been studying the extinction of frogs in Panama and Costa Rica for many years. And we showed that when the frogs disappeared, a lot of things changed: the diversity of snakes went down, there were effects on the ecology of steam, a lot of things. We thought it could affect people too, and started looking for preliminary information, but there was none.
We started thinking about possible connections. We know that frogs eat insects of all kinds. And it could be that because there was such a loss so quickly, it would result in an increase in insects. If there are no frogs, there are more insects, and this could increase insect-borne diseases like malaria. We looked at a very fine scale when the chytrid crossed an area and the number of malaria cases. And it turned out that there was a pretty significant increase in malaria cases for about 6 or 8 years after the introduction of chytrid. Compared to what is normal [malaria] levels are, it’s a big obvious change. It’s pretty crazy to think about.
G: Why do you think this happened?
KL: This is the essential question and more research should be done. What we think is that the chytrid fungus came along, it was new and wiped out 80-90% of the biodiversity of the frogs, and the natural mosquito predators disappeared, allowing the mosquitoes to multiply. Because mosquitoes are the main vector of malaria, there have been more cases of malaria.
The bottom line is that in this analysis we tried to control for all the known things normally associated with malaria, like deforestation or climate. We controlled that and there were no major changes in any of that, the only thing that changed in that time was the frog change. We can’t 100% say it was causation, but it does suggest it could be happening.
G: Could there be other public health impacts of amphibian decline?
KL: True, there are many other disease-carrying insects. Leishmaniasis is carried by these small flies; other species of mosquitoes carry other diseases. We were limited by the data available, but there could certainly be broader implications.
G: What do you think this study reveals about the broader link between biodiversity and public health?
KL: I always use the expression “we are all connected”. People cannot survive without a healthy environment. This concept of One Health, where the health of people is directly linked to the health of the environment and the health of the animals and plants that live in this environment. And whether you’re talking about food or infectious diseases, or you know, building materials about the environment, we rely on a healthy environment to provide those goods and services. And I think that’s getting better and better explained in the media, but it’s still something that doesn’t get as much attention as it should.
And that just means that conserving, protecting, and managing healthy environments is really important to all of us, everywhere on the planet.
Thanks to Alicia Benjamin for writing this article.