Central America: Amphibian deaths cause more malaria

Amphibians have been dying en masse in Central America for several years. The reason is a human-introduced fungal disease. This now has consequences for the residents: there have been more cases of malaria there since.

It was a fungus that killed amphibians. It was probably introduced by people on the go. Between the 1980s and 2000s, at least 90 species of amphibians became completely extinct in Central America and only a tenth of the original populations survived in over 400 species.

Michael Springborn was surprised that he had hardly heard of this mass extinction. After all, ecologists see it as one of the biggest losses in biodiversity due to disease. Springborn is an economist and professor in the Department of Environmental Science and Policy at the University of California Davis. “As an economist, I wanted to understand how these deaths affected human communities, to show why it matters to us when our ecosystems are destroyed,” he says.

Sharp increase in malaria cases

A possible consequence for humans was immediately found: amphibians and their larvae also feed on mosquitoes and their larvae. Mosquitoes, in turn, transmit malaria. So the death of the amphibians could have led to more malaria cases in Central America because a mosquito’s natural enemy had been severely depleted?

In fact, Springborn and colleagues noted in a recent publication in the magazine Study published on environmental research letters found that malaria cases increased dramatically during the years of amphibian extinction. Five times during peak hours, regardless of other factors such as higher temperatures, higher humidity or deforestation. These factors are known to lead to even more malaria cases. “To challenge the results, there should be another variable that changes over time, with the same spatial and temporal pattern as amphibian extinctions,” says Springborn.

The researchers could not find such a variable. It is therefore very likely that the mass extinction of amphibians has led to an increase in malaria cases. Such connections between human and animal health are not uncommon. But they are not always recognized.

Human and animal health are closely related

Already in the year 2018 showed a studythat invasive shrimp were displacing other shrimp species in the United States. However, these invasive species haven’t eaten as many mosquito larvae. So the number of mosquitoes also increased there. Presumably, the researchers write, this has also had consequences for human health.

And in many other areas too, there are connections between human and animal health and the environment. Under the keyword “One Health”, researchers are investigating precisely these links. The amphibian study is also part of this, explains Fabian Leendertz. He is professor of biology and veterinary medicine and founding director of the Helmholtz Institute for One Health in Greifswald, founded this year. “This is exactly what One Health also considers. We have an environmental factor, we have a disease, we have the animal world and therefore the very negative effect in this case,” says Leendertz. This negative effect is particularly evident in amphibians who became ill due to the fungi introduced by man. But it is also likely caused by malaria in humans.

Human-to-animal transmission – and vice versa

The Greifswald Institute studies many other interactions of this type, for example, it checks which diseases occur in wild animals that can potentially be transmitted to humans. The corona pandemic has recently shown that such zoonoses should be taken seriously. How exactly the SARS-CoV-2 virus found its way into humans is not entirely clear. However, most researchers now assume that wild animals have passed on the virus, such as sick bats.

On the other hand, human germs can also infect wild animals, explains biologist Leendertz: “We have been using the AHA rule for a long time when working with great apes. This means: keep your distance, only healthy people observe animals and we always wear face masks in the forest. “

Climate change and species extinction are increasing the problem

Both researchers believe the interrelationships between human and animal health will become more evident as species extinction and climate change increase. At the same time, Leendertz is convinced that there are already a lot of connections to see. Until now, only the data was missing.

Springborn also sees an opportunity in the research: “The good thing is that we already understand these connections better. Our efforts to mitigate the effects are increasing. And so we may even be able to mitigate the effects if they occur to a certain extent. , ” he says.