October 18, 2011 – FLAGSTAFF, Arizona — A relatively new type of drug-resistant Staphylococcus aureus could represent the world’s next bacterial epidemic, an environmental health expert said here today at a conference for science writers. The superbug, called methicillin-resistant Staphylococcus aureus strain 398, or MRSA ST398, was first identified in an infant in the Netherlands in 1994 and traced back to her family’s pigs. Now, researchers are starting to see more serious infections and some of the cases reveal no direct link to livestock, said Lance B. Price, director of the Center for Microbiomics and Human Health at The Translational Genomics Research Institute (TGen), in Flagstaff. “The rate of human [ST398] infections is going up in Denmark and the Netherlands,” Price said. “We are just looking at the beginning of an epidemic.” Price made his comments during a presentation at the 49th annual New Horizons in Science meeting, organized by the Council for the Advancement of Science Writing. The mechanism for transmission in these newer ST398 cases currently is unknown. Researchers are considering various explanations including human-to-human exposure, contaminated meat or changes in the organism that make it spread more easily, Price said.
Already, ST398 was recently found in about half of the pigs and farmers tested in Iowa. ST398 probably started out as a human-associated strain that was treatable with methicillin, a recent analysis by Price and his colleagues has revealed. Animal husbandry practices subsequently allowed the strain to spread into livestock. Meat production worldwide involves the use of life-saving human-class antibiotics as a preventive measure or production tool to keep animals healthy. However, the bacterial die-off then exercises a selection pressure on the remaining smaller population of bacteria, giving rise to antibiotic-resistant strains. With ST398, that probably led to drug-resistant strains of the bug, which were then passed back to humans via contact with livestock. “It’s a pretty sad cycle really,” Price said. Staph aureus infections can cause skin and soft tissue infections, respiratory tract infections like pneumonia, bacteremia (the presence of bacteria in the blood) and endocarditis (inflammation of the inner heart). Until the use of antibiotics in the developed world became widespread in the 1940s, these infections were often fatal. A rise in antibiotic-resistant bacteria in the past two decades means the door is open to a return to a dire medical scenario that prevailed nearly a century ago. In fact, even now, methicillin-resistant Staph aureus kills more people in the U.S. than HIV, Price said. Industrial-scale livestock farming practices are often the culprit in the proliferation of antibiotic-resistant strains of bacteria. There are 9 billion livestock animals in the U.S. (mostly broiler chickens) and 29 million pounds of active antibiotics are administered to food animals in this country each year. The animals are raised in crowded and perhaps filthy settings. The result is a profitable meat industry that makes this food affordable for much of the nation’s population (at a significant, long-term environmental cost when scaled up to current levels) but also one of the most effective systems for the evolution and transmission of antibiotic-resistant strains of bacteria that an engineer could devise, Price said. These strains persist on animal carcasses and then are passed on to humans via the meat we purchase and eat. –Scientific American
No comments:
Post a Comment