A major international study by Michigan State University and partner researchers has uncovered a hidden danger lurking in animal farms around the world: Livestock manure is packed with antibiotic resistance genes that could threaten human health.

This study spanned 14 years and represents the most comprehensive survey of livestock antibiotic resistant genes to date. The research team examined over 4,000 manure samples from pigs, chickens and cattle in 26 countries. 

“This research shows that what happens on farms doesn’t stay on farms,” said James Tiedje, a world-renowned expert in microbiology at MSU and one of the authors of the study. “Genes from manure can make their way into the water we drink, the food we eat and the bacteria that make us sick.”

To better understand the risk, the research team built a global map highlighting regions where dangerous antibiotic resistance genes are most common. They also developed a new system to rank which genes pose the greatest threat to human health, especially those that are mobile, hard to treat, and already found in or prone to transfer to disease-causing bacteria.