Study highlights importance of biodiversity for human health

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Dozens of species of frogs, salamanders and other amphibians quietly disappeared from parts of Latin America in the 1980s and 2000s with little notice from humans, apart from a small group of environmentalists. Yet the decline of amphibians has had direct consequences for people’s health, according to a study from the University of California, Davis.

The study, published in the journal Environmental Research Letters, links massive amphibian mortality in Costa Rica and Panama to a spike in malaria cases in the region. At the height of the peak, up to 1 in 1,000 people annually contract malaria that would not normally have occurred if amphibian mortality had not occurred, according to the study.

“Stable ecosystems underpin all kinds of aspects of human well-being, including regulatory processes important for disease prevention and health,” said lead author Michael Springborn, a professor in the Department of Science and UC Davis environmental policies. “If we allow massive disruptions to ecosystems to occur, it can have a huge impact on human health in ways that are hard to predict in advance and hard to control once they are underway.”

A natural experience

From the early 1980s to the mid-1990s, a deadly fungal pathogen called Batrachochytrium dendrobatidis, or “Bd”, has traveled across Costa Rica, devastating amphibian populations. This amphibian chytrid fungus continued eastward through Panama in the 2000s. Globally, the pathogen has led to the extinction of at least 90 species of amphibians and the decline of at least 500 additional species.

Shortly after the massive amphibian kills in Costa Rica and Panama, both countries experienced a spike in malaria cases.

Some frogs, salamanders and other amphibians eat hundreds of mosquito eggs every day. Mosquitoes are a vector of malaria. Scientists have wondered if the amphibian crash could have influenced the increase in malaria cases?

To find out, the researchers combined their knowledge of amphibian ecology, data from newly digitized public health records, and data analysis methods developed by economists to take advantage of this natural experiment.

“We have known for some time that there are complex interactions between ecosystems and human health, but measuring these interactions is still incredibly difficult,” said co-author Joakim Weill, who holds a Ph.D. candidate at UC Davis when the study was conducted. “We got there by merging tools and data that don’t usually go together. I didn’t know what herpetologists were studying until I collaborated with one!”

The results show a clear link between when and where the fungal pathogen spreads and when and where malaria cases increase. The scientists note that while they cannot rule out another confounder completely, they found no evidence of other variables that could both lead to malaria and follow the same mortality pattern.

Tree cover loss was also associated with an increase in malaria cases, but not to the same extent as amphibian loss. Typical levels of tree canopy loss increase annual malaria cases to 0.12 cases per 1,000 people, compared to 1 in 1,000 for amphibian mass mortality.

Trade threats

The researchers were motivated to conduct the study by concerns about the future spread of similar diseases through the international wildlife trade. For instance, Batrachochytrieum salamandrivoransor “Bsal”, also threatens to invade ecosystems through global trade markets.

Springborn said measures that could help prevent the spread of pathogens to wildlife include updating trade regulations to better target species that harbor such diseases as our knowledge of threats evolves.

“The costs of putting these protective measures in place are immediate and obvious, but the long-term benefits of avoiding ecosystem disruptions like this are harder to assess but potentially enormous, as this article shows. “, said Springborn.

Additional co-authors include Karen Lips from the University of Maryland, Roberto Ibáñez from the Smithsonian Tropical Research Institute in Panama, and Aniruddha Ghosh from UC Davis and the Alliance of Biodiversity International and CIAT in Kenya.

The study was funded by the National Science Foundation and the UC Davis Institute of the Environment.

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