Status: 10/31/2022 12:21 p.m
Amphibians have been dying en masse in Central America for several years. The reason is a fungal disease introduced by humans. This now has consequences for the residents: Since then there have been more cases of malaria there.
It was a fungus that killed the amphibians. It was probably introduced by traveling people. Between the 1980s and 2000s, at least 90 species of amphibians became completely extinct in Central America, and in over 400 species, only a tenth of the original populations survived.
Michael Springborn was surprised that he had hardly heard anything about this mass extinction. After all, ecologists consider it one of the greatest 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 was keen to understand how these deaths had affected human communities, to show why it is relevant to us when our ecosystems are being destroyed,” he says.
Sharp increase in malaria cases
A possible consequence for humans was quickly found: amphibians and their larvae also feed on mosquitoes and their larvae. Mosquitoes, in turn, transmit malaria. So could the amphibian die-off have led to more cases of malaria in Central America because a mosquito’s natural enemy had been severely depleted?
Indeed, Springborn and colleagues noted in a recent publication in the journal Environmental Research Letters published study found that malaria cases increased drastically during the years of amphibian extinction. Fivefold at peak times, regardless of other factors such as higher temperatures, more humidity or deforestation. These factors are known to also lead to more cases of malaria. “To challenge the results, there would have to be another variable changing over time, with the same spatial and temporal pattern as in 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 the 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 crayfish were crowding out other crayfish species in the United States. However, these invasive species did not eat as many mosquito larvae. So the number of mosquitoes also increased there. Presumably, the researchers write, this also had consequences for human health.
And in many other areas, too, there are connections between the health of humans, animals and the environment. Under the keyword “One Health”, researchers are investigating precisely these links. The study on amphibians is also part of this, explains Fabian Leendertz. He is a professor of biology and veterinary medicine and founding director of the Helmholtz Institute for One Health in Greifswald, which was founded this year. “That’s exactly what One Health also looks at. We have an environmental factor, we have an illness, we have the animal world and then the very negative effect in this case,” says Leendertz. This negative effect is particularly evident in the amphibians that became ill from the fungi introduced by humans. But it’s probably also caused by malaria in humans.
Transmission from human to animal – and vice versa
The institute in Greifswald investigates many other interactions of this kind. For example, it monitors which diseases occur in wild animals that can potentially be transmitted to humans. The corona pandemic recently showed that such zoonoses should be taken seriously. How exactly the Sars-CoV-2 virus found its way to humans is not entirely clear. However, the majority of researchers now assume that wild animals have transmitted the virus, for example 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 very long time when we work with great apes. That means: keep your distance, only healthy people watch the animals and we always wear face masks in the forest.”
Climate change and species extinction are increasing the problem
Both researchers believe that the interrelationships between human and animal health will become more apparent as species extinction and climate change increase. At the same time, Leendertz is convinced that there are already many connections to be seen. So far, only the data was missing.
Springborn also sees an opportunity in research: “The positive thing is that we already understand these connections better. Our efforts to mitigate the effects are increasing. And so we may also be able to mitigate the effects if they happen until to a certain extent,” he says.