A Miracle Drug Is Saving People but Destroying the Environment

Ivermectin is wiping out dung beetles, which keep the world from drowning in manure.
(Photo: George Grall/‘National Geographic’/Getty Images)
Aug 5, 2016· 2 MIN READ
Richard Conniff is the author of House of Lost Worlds: Dinosaurs, Dynasties, and the Story of Life on Earth and other books.

See if you can spot the pattern here: Widespread reliance on the herbicide Roundup has pushed the monarch butterfly to the brink of extinction. Neonicotinoid pesticides stand accused of knocking down populations of honeybees and other pollinating insects. The veterinary drug diclofenac has killed off 99.9 percent of the vultures in India. Now it looks as though ivermectin, long hailed as a miracle drug, may be doing the same thing to dung beetles everywhere.

Yep, it’s definitely a pattern: Companies find some alleged wonder product and move it to market as quickly as possible, with a tight focus on profits and no regard (or responsibility) whatever for the inadvertent side effects.

The dung beetle story has gotten relatively little attention, perhaps because people have the idea that these funny little feces eaters exist only in Africa and only to help clear the landscape of gargantuan elephant droppings. There are 5,000 dung beetle species, and they do their humble work on every continent except Antarctica. If you think dung beetles don’t matter pretty much everywhere, try imagining a world neck-deep in cattle manure.

Let’s concede up front that as part of the human medical tool kit, ivermectin is one of the great miracle drugs of our time. It kills parasites and has thus saved hundreds of millions of people from the horribly devastating effects of both river blindness and elephantiasis. The scientists who developed the drug in the 1970s shared the Nobel Prize last year for their work.

Ivermectin is, however, also one of the world’s most popular veterinary drugs, for a host of parasitic afflictions. That’s a problem because livestock grazing eats up about a quarter of the world’s ice-free land, and the livestock excrete all but a fraction of the ivermectin intact back into the environment, where it continues its killing ways.

A study early this year linked ivermectin use to the decline of seven dung beetle species in Spain and Portugal. Now the journal Environmental Toxicology and Chemistry has put dung beetles on the cover and devoted the bulk of the magazine to the ivermectin problem.

The most important of the studies looks at ivermectin use in four countries and suggests ways to minimize those inadvertent side effects. “As expected, the overall number and diversity of dung beetles, dung flies, and parasitoid wasps decreased as the ivermectin concentration increased,” said coauthor Wolf Blanckenhorn, an evolutionary biologist at the University of Zurich.

Earthworms and springtails living in the ground underneath the cow pats appeared to be unaffected. These other species were sufficiently insulated from the ivermectin, or sufficiently resistant to it, to compensate for the loss of dung beetles, so the dung degraded more or less normally. Nature is like that. It has redundancies and backup systems, also known as biodiversity.

It’s worth noting that the previous study in Spain and Portugal was not nearly so sanguine. Those researchers reported that routine use of ivermectin in cattle not only impaired the dung beetles but also caused an extra 312 pounds of dung to accumulate per acre per year. That’s bad news even for cattle farmers, who cannot graze their cattle on fields smothered in dung. It’s bad news for the environment too. Stripping away backup systems is simply reckless, whether you are talking about nature or engineering. Sooner or later, everything goes kerflooey.

For their study, Blanckenhorn and his coauthors field-tested a method for identifying the effects of ivermectin on a range of dung-eating species. The aim is to give government regulatory bodies—and progressive farmers—a tool to determine when it’s safe to use ivermectin and what minimal dose can treat the livestock without disrupting the natural environment. Now government agencies need to decide whether to require “this more conclusive yet more complex test,” said Blanckenhorn. Taking a census of the dung-eating population in a field could soon become easier because of DNA bar coding, which uses rudimentary genetic sequencing to quickly identify the species present in a sample.

Meanwhile, farmers might want to think twice about their dependence on ivermectin or the host of other drugs being pushed on them by heedless pharmaceutical companies. The rest of us? We have one more reason to continue reducing the amount of meat in our diets.