The Mushroom That Killed the Frogs — and Led to Malaria
Michael Springborn, lead author of the paper and professor and environmental and resource economist at UC Davis said: “Although Bd swept across Central America from the 1980s to the 2000s, the analysis does demonstrate its impact on human health. “Data exists, but it is not easily obtained,” he said. Over the years, however, county-level disease records have been digitized at health ministries in Costa Rica and Panama, providing an opportunity to combine that epidemiology in a specific statistical model with satellite imagery. Astronomical and ecological surveys show soil characteristics and rainfall. as well as data on the decline of amphibians.
“We always thought if we could link [the die-off] with people, more people will be interested,” says Lips. “We’re pretty sure we can quantify changes in bugs, or frogs, or water quality, fish or crabs or shrimp. But making that connection with people is very difficult, because the effect is so pervasive, and it happens over such a large area.”
But precisely because Bd swept across Central America in a particular pattern, northwest to southeast — “a wave that hits county to county over time,” says Springborn — it created an experiment. nature allowed researchers to look at Costa Rica and Panama in detail before and after the wave of mushrooms arrived. In the health records, they were able to discern that malaria rates in the counties (called states or distritos) remained constant before the Bd fungus took hold, and then began to increase after that. At the height of the epidemic, six years after Bd arrived in an area, the number of malaria cases increased fivefold.
And then they started to fall again, starting about eight years after the deadly fungus appeared. The researchers aren’t sure why, because most amphibian populations have not recovered to the fungal attack. Although some populations seem to develop resistance, most have not yet recovered their density or diversity. Since fungi survive in the environment, they are still at risk of becoming infected.
There is one missing piece in the researchers’ analysis, which is that there are no concurrent data to demonstrate that mosquito populations spike in a way that promotes malaria. The surveys they needed – on mosquito densities during and after Bd arrival, in 81 counties in Costa Rica and 55 in Panama – simply did not exist. That makes it difficult for them to determine why malaria is breaking out, especially when frog populations haven’t recovered. Springborn theorized that it could be due to human intervention, like governments or organizations noticing an increase in malaria and spraying insecticides or distributing bed nets. Or it could be that the ecosystem has recovered although the frogs have not, with other predators taking advantage of the empty niches to suppress mosquito populations.
But the fact that the rate of malaria returns does not detract from the significance of the study’s findings. “For the most part, Bd is a story about the consequences for amphibians, basically: Is it too bad to lose this fascinating group of creatures?” James P. Collins, an evolutionary ecologist and professor at Arizona State University. (Collins has some involvement in this research; he oversaw a grant that the National Science Foundation gave Lips in the 1990s.) Connecting the dots to the real effects on people is a nice proof to understand the consequences. “