the collapse of frog populations leads to malaria outbreaks

LThe One Health concept, better known by its original name One Health, has invaded public health discourse. Adopting or promoting an integrated approach of the human, animal and environmental spheres to face future health crises almost takes the place of an imposed figure to apply for a position or for funding. All researchers know the risk: hiding a poor science behind a rich concept.

The study just published by the journal Environmental research letters on the contrary, he promises to make an appointment. For the first time, a team of researchers highlights the link between the collapse of an animal population and a human health crisis. And not just any one: on the one hand, the carnage caused by the fungus Batrachochytrium dendrobatidis (Bd), which makes amphibians the most endangered animal group, according to the International Union for Conservation of Nature. On the other, malaria, the scourge responsible for 627,000 deaths in 2020.

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The researchers set sail for Costa Rica and Panama. Before BD’s arrival in Central America in the mid-1980s, these two countries were jewels of amphibious biodiversity. The fungus wreaked havoc there: 500 species have declined, another 90 have simply and simply disappeared.

Karen Lips of the University of Maryland had followed the crisis on the front line. “During a discussion, we wondered what could have wreaked such havoc on human healthsays Michael Springborn, an environmental economist at the University of California Davis. As amphibians are known to eat mosquitoes and mosquitoes transmit malaria, we decided to go and see what was happening with the malaria attacks in these two countries. “

“A natural experiment”

The two researchers and their colleagues knew that they had detailed data on the trend of the fungus: year after year, local authorities have listed its trend, through the 136 cantons, from the northwest to the southeast of Costa Rica, between 1986 and 1993, then from west to east of Panama, from 1993 to 2010.

They collected information, on the same scale, on cases of malaria. The result is spectacular: three years after the first significant declines of frogs, toads or salamanders, the crates explode and remain on a plateau (more than one in a thousand people) for six years, before falling.

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The mechanism seems obvious enough: amphibians devour insects, especially their larvae, tadpoles gorge themselves on mosquito eggs, and larvae that float in ponds. In what proportion? In the absence of data on mosquito density in Central America, researchers suggest rare work elsewhere: a study conducted in Indiana in 2003 showed a 98% decline in mosquito larvae populations in the presence of salamanders. And the conclusion to impose itself: fewer amphibians, more insects and therefore more malaria.

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