Laxminarayan and his colleagues were convinced that farm-created resistance was posing an equivalent danger to livestock, but—unlike in human medicine—there were no large data sources to help them prove it. Surveillance for resistance on farms is patchy and politically sensitive. They turned instead to searching for projects in which researchers had measured resistance in animals and meat at single moments in time.
They ended up finding thousands of studies published in multiple languages, a set they then narrowed down to 901 in which the science seemed robust. The surveys had been performed in 822 locations across the world, and collectively reported analyses of 285,496 samples taken from animals.
Processed together, the surveys revealed rising rates of resistance in animals across a wide swath of antibiotics. That includes the newer, more complex drugs that replaced the older, cheaper ones lost to resistance. The biggest increases appeared to be in parts of the world where industrial-scale farming has expanded and regulation has not kept up. Though for some countries, that turned out to be hard to prove: Some of the largest meat-producing countries had the least available data.
The breadth of the problem worries Lance Price, a microbiologist and the founding director of the Antibiotic Resistance Action Center at George Washington University, whose work focuses on antibiotic use in food-animal production. (He was not involved in the study.)
He points out that the most virulent, multidrug-resistant pathogens emerge almost by accident, through the fortuitous accumulation of a few pieces of genetic material within a single bacterium. Those combinations occur only where lots of antibiotics are being used in lots of animals at once, and until recently, they have been rare. “But if you use antibiotics in billions of animals around the globe, you are creating the opportunity for rare events to be no longer rare,” Price says. “This creates lots of possibilities for new resistance elements to emerge.”
One reason developing-world agriculture relies so heavily on antibiotics is that they allow farms to operate at low margins, without spending scarce funds on veterinary care or disease containment. But poor animal hygiene and lax biosecurity don’t only create the conditions that demand antibiotics—they also allow bacteria to flow off farms and into the wider world, increasing the chances that resistant bacteria could reach and sicken humans as well.
If there’s a bright spot in the analysis, it is that it illuminates not only where antibiotic misuse is a problem but also where it is not one—yet. For instance, surveys from sub-Saharan Africa showed that rates of resistance were still low in most countries. That may be a signal that animal agriculture hasn’t intensified as much as it has in Asia, and that there may be time to influence those countries to go a different way.
“We shouldn’t look at low- and middle-income countries as a single group,” says Thomas Van Boeckel, an epidemiologist at ETH Zurich and the paper’s first author. “Some countries are in a dire state, but others don’t have much of a problem.”
That diversity may also indicate where political pressure could make the most difference. Three years ago, the United Nations General Assembly held an all-day meeting on the problem of antibiotic misuse in medicine and agriculture, only to hear from some countries’ representatives that feeding their own people was a much higher priority than attending to global public health.
Knowing which countries or locations are resistance hotspots, and focusing efforts on them, could help soothe that tension. It could shore up small-scale farming in areas where animals are critical to families’ survival. And it might give international donors, not to mention affluent nations, some guidance for where their funds could offer the most help.