Feeding antibiotics to healthy livestock is leading to an emerging human health crisis—one scientists and government officials have seen coming for decades.
Stuart Levy once kept a flock of chickens on a farm in the rolling countryside west of Boston. No ordinary farmer, Levy is a professor of molecular biology and microbiology and of medicine at Tufts University School of Medicine. This was decades ago, and his chickens were taking part in a never-before-conducted study. Half the birds received feed laced with a low-dose of antibiotics, which U.S. farmers routinely administer to healthy livestock — not to cure illness, but merely to increase the animals’ rates of growth. The other half of Levy’s flock received drug-free food.
Results started showing up almost instantly. Within two days, the treated animals began excreting feces containing E. coli bacteria that were resistant to tetracycline, the antibiotic in their feed. (E. Coli, most of which are harmless, normally live in the guts of chickens and other warm-blooded animals, including humans.) After three months, the chickens were also excreting bacteria resistant to such potent antibiotics as ampicillin, streptomycin, carbenacillin, and sulfonamides. Even though Levy had added only tetracycline to the feed, his chickens had somehow developed what scientists now call “multi-drug resistance” to a host of antibiotics that play important roles in treating infections in people. More frightening, although none of the members of the farm family tending the flock were taking antibiotics, they, too, soon began excreting drug-resistant strains of E. coli.
When Levy’s study was published in The New England Journal of Medicine in 1976, it was met with skepticism. “The other side — industry — could not believe that this would have happened. The mood at the time was that what happens in animals does not happen in people,” said Levy, who serves as president of the Alliance for the Prudent Use of Antibiotics, in a telephone interview from his office at Tufts. “But we had the data. It was obvious to us even then that using antibiotics this way was an error and should be stopped.”
During the intervening 35 years, study after study has confirmed Levy’s findings and shown that the problem of antibiotic-resistant “superbugs” is even worse than anyone could have imagined. Each year, 70,000 Americans in U.S. hospitals die from bacterial infections that drugs are unable to kill. And even as the number of infectious diseases is on the rise, more antibiotics are administered to livestock than ever before, from 17.8 million pounds per year in 1999 according to the Animal Health Institute (a trade organization of companies, like Bayer, Novartis, and Pfizer, that manufacture livestock drugs) to 29.8 million pounds in 2009, according to the U.S. Food and Drug Administration, or FDA. Fully 80 percent of the antibiotics used in the United States are given to livestock, and the vast majority are administered to promote growth and stave off potential infections, not to treat illness.
From his perspective of more than three decades as a resistant-microbe watcher, Levy sounded almost weary when he said, “Proponents of growth promotion keep asking for more data, and we scientists provide them. But then the findings have never led to removal of the practice.”
Earlier this week, the Natural Resources Defense Council, Center for Science in the Public interest, Food Animal Concerns Trust, Public Citizen, and the Union of Concerned Scientists joined forces to file a lawsuit against the FDA. The groups want the agency to withdraw its approval for most non-therapeutic uses of penicillin and tetracycline in animal feed. They say that it’s something regulators should have done decades ago.
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