On the other hand, the success of the E.U.’s ban is less than clear-cut. “The studies show that the E.U.’s curtailing of these compounds in feed has resulted in more sick animals needing higher therapeutic doses,” Carnevale says.
“There are cases of that,” admits Scott McEwen, a University of Guelph veterinary epidemiologist who advises the Canadian government on the public-health implications of livestock antibiotics. At certain stressful times in a young animal’s life, as when it is weaned from its mother, it becomes particularly susceptible to disease. “The lesson,” he says, “may be that we would do well by being more selective than a complete ban.”
McEwen and many of his colleagues see no harm in using growth-promoting livestock antibiotics known as ionophores. “They have no known use in people, and we see no evidence that they select for resistance to important medical antibiotics,” he says. “So why not use them? But if anyone tries to say that we should use such critically important drugs as cephalosporins or fluoroquinolones as growth promoters, that’s a no-brainer. Resistance develops quickly, and we’ve seen the deleterious effects in human health.”
A thornier issue is the use of antibiotics to treat sick livestock and prevent the spread of infections through crowded herds and flocks. “Few people would say we should deny antibiotics to sick animals,” McEwen says, “and often the only practical way to administer an antibiotic is to give it to the whole group.” Some critics have called for restricting certain classes of critically important antibiotics from livestock use, even for treating sick animals. For instance, the FDA is considering approval of cefquinome for respiratory infections in cattle. Cefquinome belongs to a powerful class of antibiotic known as fourth-generation cephalosporins, introduced in the 1990s to combat hospital infections that had grown resistant to older drugs. In the fall of 2006, the FDA’s veterinary advisory committee voted against approving cefquinome, citing concerns that resistance to this vital class of drug could spread from bacteria in beef to hospital superbugs that respond to little else. But the agency’s recently adopted guidelines make it difficult to deny approval to a new veterinary drug unless it clearly threatens the treatment of a specific foodborne infection in humans. As of press time, the FDA had yet to reach a decision.
Image courtesy of Jessica Snyder Sacs
Consumers may contribute to the problem of DNA pollution whenever they use antibacterial soaps and cleaning products. These products contain the antibiotic-like chemicals triclosan and triclocarban and send some 2 million to 20 million pounds of the compounds into the sewage stream each year. Triclosan and triclocarban have been shown in the lab to promote resistance to medically important antibiotics. Worse, the compounds do not break down as readily as do traditional antibiotics. Rolf Halden, cofounder of the Center for Water and Health at Johns Hopkins University, has shown that triclosan and triclocarban show up in many waterways that receive treated wastewater—more than half of the nation’s rivers and streams. He has found even greater levels of these two chemicals in sewage sludge destined for reuse as crop fertilizer. According to his figures, a typical sewage treatment plant sends more than a ton of triclocarban and a slightly lesser amount of triclosan back into the environment each year.
For consumer antibacterial soaps the solution is simple, Halden says: “Eliminate them. There’s no reason to have these chemicals in consumer products.” Studies show that household products containing such antibacterials don’t prevent the spread of sickness any better than ordinary soap and water. “If there’s no benefit, then all we’re left with is the risk,” Halden says. He notes that many European retailers have already pulled these products from their shelves. “I think it’s only a matter of time before they are removed from U.S. shelves as well.”
Consumers may contribute to the problem of DNA pollution whenever they use soaps and cleaning products containing antibiotic-like compounds.
Finally, there is the complicated matter of the vast quantity of antibiotics that U.S. doctors prescribe each year: some 3 million pounds, according to the Union of Concerned Scientists. No doctor wants to ignore an opportunity to save a patient from infectious disease, yet much of what is prescribed is probably unnecessary—and all of it feeds the spread of resistance genes in hospitals and apparently throughout the environment.
“Patients come in asking for a particular antibiotic because it made them feel better in the past or they saw it promoted on TV,” says Jim King, president of the American Academy of Family Physicians. The right thing to do is to educate the patient, he says, “but that takes time, and sometimes it’s easier, though not appropriate, to write the prescription the patient wants.”
Curtis Donskey, chief of infection control at Louis Stokes Cleveland VA Medical Center, adds that “a lot of antibiotic overuse comes from the mistaken idea that more is better. Infections are often treated longer than necessary, and multiple antibiotics are given when one would work as well.” In truth, his studies show, the longer hospital patients remain on antibiotics, the more likely they are to pick up a multidrug-resistant superbug. The problem appears to lie in the drugs’ disruption of a person’s protective microflora—the resident bacteria that normally help keep invader microbes at bay. “I think the message is slowly getting through,” Donskey says. “I’m seeing the change in attitude.”
Meanwhile, Pruden’s students at Colorado State keep amassing evidence that will make it difficult for any player—medical, consumer, or agricultural—to shirk accountability for DNA pollution.
Late in the afternoon, Storteboom drives past dairy farms and feedlots, meatpacking plants, and fallow fields, 50 miles downstream from her first DNA sampling site of the day. Leaving her Jeep at the side of the road, she strides past cow patties and fast-food wrappers and scrambles down an eroded embankment of the Cache la Poudre River. She cringes at the sight of two small animal carcasses on the opposite bank, then wades in, steering clear of an eddy of gray scum. “Just gross,” she mutters, grateful for her watertight hip boots.
Of course, the invisible genetic pollution is of greater concern. It lends an ironic twist to the river’s name. According to local legend, the appellation comes from the hidden stashes (cache) of gunpowder (poudre) that French fur trappers once buried along the banks. Nearly two centuries later, the river’s hidden DNA may pose the real threat.
