Some spikes in malaria cases may be tied to amphibian die-offs
Fewer mosquito-eaters may have left more blood-suckers to spread the disease
Amphibians worldwide have died in record numbers from a fungal disease. In Central America, their loss may be tied to a bump up in cases of malaria — a disease spread to people by mosquitoes.
The fungal disease has a long name: chytridiomycosis (Kih-TRID-ee-oh-my-KOH-sis).
Sales of amphibians have helped spread this chytrid disease around the world. This has driven the largest disease-related loss of biodiversity ever recorded. At least 500 amphibian species worldwide have declined. Ninety of those species are now extinct. Frogs and toads in the Americas and Australia have taken the biggest hit.
Amphibians can play a role in keeping mosquito numbers down. Tadpoles and other amphibian larvae feed on mosquito larvae. Adult amphibians compete with the insects in other ways, such as places to live. So fewer frogs, toads and salamanders may leave more mosquitoes to spread malaria.
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Scientists wanted to know if these losses might affect people’s health. To find out, they turned to surveys, health records and satellite data from Costa Rica and Panama. The disease has killed amphibians there since the 1980s.
The new study focused on each county in these countries. And it turned up a temporary boost in cases — roughly one more case per 1,000 people per year. These increases emerged a few years after local amphibian losses. They lasted about six years at each location. The scientists reported their findings September 20 in Environmental Research Letters.
This shows how biodiversity loss can “ripple through ecosystems and affect humans,” says study leader Michael Springborn. He’s an environmental economist. He works at the University of California, Davis. Being aware of such impacts may prompt people to try to head off future ecological threats, he says.
The fungal disease moved like a wave across ecosystems in both Costa Rica and Panama. These nations sit side by side on a narrow strip of land. Springborn’s team figured out when the fungus appeared in different areas. Then the researchers compared numbers of malaria cases before and after each area’s amphibian die-offs.
Malaria rates rose in the first few years after the fungal infections hit local amphibians. Malaria cases in these places stayed high for the next six years or so. There aren’t data to prove that mosquito numbers actually climbed after the die-offs, the researchers say. After those six years, the case counts fell again. Why they dropped is still not clear.
Such studies as this one might “help motivate [wildlife] conservation,” says Hillary Young. She’s a community ecologist who did not take part in the new study. Young works at the University of California, Santa Barbara.
“Humans are causing wildlife to be lost at a rate similar to that of other major mass-extinction events,” she says. “We are increasingly aware that these losses can have major impacts on human health and well-being.”