An orange toad perched on a leaf
An orange toad perched on a leaf

Past Malaria Surges Linked to Amphibian Die-off

A study suggests that pathogens affecting other species can indirectly harm human health.

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Andy Carstens

Andy Carstens is a current contributor and past intern at The Scientist. He has a bachelor’s degree in chemical engineering from the Georgia Institute of Technology and a master’s in science writing from Johns Hopkins University. Andy’s work has also appeared in Audubon, Slate, Them, and Aidsmap.

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ABOVE: A golden toad (Bufo periglenes), declared extinct from its range in Costa Rica in 2004, in part due to chytrid fungus US Fish and Wildife Service

Spikes in malaria cases that occurred in Costa Rica and Panama between the 1990s and early 2000s may have occurred because the deadly Batrachochytrium dendrobatidis fungus decimated amphibians in those countries. Research published yesterday (September 20) in Environmental Research Letters suggests severe declines in mosquito-devouring frogs, toads, and salamanders caused by the pathogen, also known as chytrid fungus, may have allowed malaria-spreading mosquito populations to thrive unchecked—an example of how biodiversity loss can have hidden consequences for humans.

See “Origin of Frog-Killing Chytrid Fungus Found

“The results in our paper suggest that some policies, such as amphibian conservation policies or the regulation of wildlife trade, could have benefits for human health which are not currently accounted for,” study author Joakim Weill told Anthropocene in 2020, after a preprint of the study was posted on medRXiv.

Past assessments had established the fungus’s journey across the region: It first appeared in the northwest of Costa Rica in the 1980s, advanced southeast across the country through the mid-1990s, and then pushed east into Panama in the 2000s, the study authors write. The researchers used county-level health data to compare the spread of malaria in humans to the wave of chytrid fungus that infected amphibians, revealing that malaria cases surged a few years after amphibians started dying, reports New Scientist. In Panama, for example, malaria cases increased five fold after the fungus arrived, according to the outlet.

See “Frogs Fight Back From Fungal Attack

The researchers estimate that amphibian deaths were responsible for one-half to two-thirds of malaria cases in the affected areas during the surges that occurred in the 1990s and early 2000s, but study author Michael Springborn tells New Scientist that higher rainfall also contributed. Since those surges, malaria cases have fallen in both countries, which Springborn tells the outlet may be due to public health measures or to increases in populations of other mosquito-slurping animals.

The results indicate how imbalances in ecosystems can affect human health, New Scientist reports, and Springborn tells the outlet, “Predicting these things ahead of time is pretty difficult.”