Breeding an Epidemic Antibiotics and Meat

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

THE ANIMAL-HUMAN LINK

Those groups opposed to, and those in favor of, subtherapeutic use of antibiotics in livestock spent most of the 1960s and '70s arguing about whether resistant bacteria developed in animal populations could be transferred to and infect humans. Today it's fairly clear that this does happen, but there's still much argument about how widespread the problem is.

Most bacteria present in cattle, for example, don't seem to do well in humans . . . each species has its own set of microorganisms well adapted to their particular environment. An exception, however, is the genus Salmonella, with its ten common species. In England, a rash of 305 cases of Salmonella typhimurium in the '60s and early '70s—an outbreak that resulted in the deaths of two adults and a child—led that country to ban subtherapeutic use of antibiotics. In 1976, there was a Salmonella heidelberg outbreak in Connecticut. The bacteria were found in calves, then in the farmer who kept the calves, then in his pregnant daughter, then in his daughter's baby three days after birth, and finally in other babies kept in the same hospital nursery. At the time, it wasn't possible to prove the existence of a direct path for the salmonella from the calves to the babies in the nursery, but the circumstantial evidence was very strong.

The most heralded example of salmonella transfer from livestock to humans—the one that seems finally to have proven the link to most scientists' satisfaction—occurred two years ago but has only recently received much publicity. A Minnesota couple became seriously ill after taking penicillin for a cold and were found to be infected by a resistant strain of Salmonella newport. A Centers for Disease Control researcher, Dr. Scott Holmberg, was brought in and used a new technique called genetic fingerprinting to track the salmonella to hamburger, back through a supermarket, and finally to a South Dakota farm where a herd of cattle was being fed subtherapeutic doses of chlortetracycline.

Dr. Holmberg eventually traced the same strain of Salmonella newport to 18 other peo ple in four states. Eleven had been hospitalized, and one had died. Most of the infected people had handled the meat from the farm before it was cooked. Salmonella are killed by heat—as yet, there's little evidence that eating cooked meat from livestock raised on antibiotics is in itself unhealthy—but the bacteria are so virulent that they were able to enter the bodies of the people who had prepared or otherwise come in contact with the raw meat. What's more, 12 of the 18 had been taking penicillin or other antibiotics for cold symptoms.

RSS | Comments | E-mail | Print