The sight of just one boot coming through the doorway cues the clatter of tiny hoofs as 500 piglets scramble away from Mike Male. “That's the sound of healthy pigs,” shouts Male, a veterinarian who has been working on pig farms for more than 30 years. On a hot June afternoon, he walks down the central aisle of a nursery in eastern Iowa, scoops up a piglet and dangles her by her hind legs. A newborn piglet's navel is an easy entry point for bacterial infections, he explains. If this pig were infected, she would have an abscess, a lump of inflamed tissue, just below the navel. “In human terms, she'd be an outie instead of an innie,” he says, rubbing the pig's healthy, pink belly button.
Nearly six years ago, an outbreak of 'outies' at this nursery marked the first known infection with methicillin-resistant Staphylococcus aureus (MRSA) in pigs in the United States. MRSA has troubled hospitals around the world for more than four decades and has been infecting people outside of health-care settings since at least 1995 (see Nature 482, 23–25; 2012). It causes around 94,000 infections and 18,000 deaths annually in the United States. In the European Union, more than 150,000 people are estimated to contract MRSA each year. Its first appearance on a US farm signalled the expansion of what many believe is a dangerous source of human infection.
Male investigated the infections with Tara Smith, an epidemiologist at the University of Iowa in Iowa City, who has since launched one of the most comprehensive investigations yet of where MRSA lives and how it spreads into and out of agricultural settings. She has surveyed farms and grocery stores as well as people's homes, noses and pets. Her findings could help to end a raging debate about whether farms' use of antibiotics is contributing to the rise of drug-resistant bacterial infections in humans.
Scientists and health experts fear that it is, and that drug-resistant bacteria from farms are escaping via farmworkers or meat. Last year, the US Food and Drug Administration (FDA) recommended more restraint in the use of antibiotics in livestock, following the lead of regulatory authorities in other countries (see Nature 481, 125; 2012).
But the meat and agricultural industries are fighting those restrictions. They claim that MRSA and other drug-resistant bacteria that cause human infections arise in hospitals, and that meat production includes safety measures, such as sanitation rules in slaughterhouses, that prevent resistant bacteria from spreading to and infecting people. “There's a long way between the farm and the table,” says Ron Phillips, a representative for the Animal Health Institute, a trade organization based in Washington DC that represents veterinary-medicine companies.
The major problem has been lack of data. Many farmers are reluctant to allow scientists access to their facilities, and farmworkers — many of whom, in the United States, are undocumented immigrants — are wary of anyone who might want to sample them. But Smith and a small group of researchers are starting to fill the void. They have “really shaped the state of knowledge in the United States”, says Christopher Heaney, an epidemiologist at Johns Hopkins University in Baltimore, Maryland. Smith's current research, says Heaney, could allow officials to “truly say where these bacteria in people's noses are coming from”.
Profit and loss
At a concentrated animal-feeding operation (CAFO) about an hour's drive west from Ames, Iowa, the usual din of the nursery is punctuated by the sound of piglets sneezing, thanks to an outbreak of H1N2 influenza. Craig Rowles, a veterinarian and the farm's manager, surveys his charges, some of which have mucus dripping from their snouts. “It's just like when you bring kids to a day-care centre,” he says. “After a while, they're going to come home with a snotty nose.”