Agriculture industry science denial?
The decrease in the usage of antibiotics has led to a measurable decrease in antibiotic-resistance in bacteria found in animals, Henriksen said. For example, resistance to macrolide antibiotics in campylobacter bacteria in pigs was reduced to 20 percent in 2006, compared with 80 percent pre-ban levels, he said. Resistance to vancomycin antibiotics in enterococci bacteria in broiler chickens was reduced to 5 percent in 2006 compared with a 75 percent resistance prior to the ban.
Antibiotic resistance in bacteria found in meat for consumption has also decreased, Henriksen said. In E. coli bacteria found in broiler meat, the incidence of resistance to cephalosporin antibiotics was less than 5 percent, compared with 35 percent in other EU countries, he said. At the same time, animal production in Denmark has increased, and animal health has not been compromised, Henriksen said.
Frank Aarestrup, director of the Antimicrobial Resistance and Molecular Epidemiology Unit at the Danish Food Institute said in testimony prepared for the 2009 hearing that there had been a gradual increase in the mortality of young pigs after the ban, but that rates had since fallen to pre-ban levels. In addition, the average number of pigs produced per sow, which he said was a key indicator of pig health and welfare, increased from 21 to 25 from 1992 to 2007, while overall swine production increased from 18.4 million pigs to 26.3 million pigs, a 43 percent increase, in the same time period.
Industry: there’s no proof!
The livestock industry denies that there is a link between the non-therapeutic use of antibiotics in animals and increased resistance to antibiotics in microbes infecting humans. Such a claim is “not based on any science,” said Dave Warner, spokesman for the National Pork Producers Council, a swine industry trade association.
Remapping Debate asked Warner if there was evidence that antibiotic use in animals leads to antibiotic resistant bacteria in animal infections. Warner conceded that there was. But he said there was no evidence that antibiotic-resistant bacteria in animals poses a human health risk.
Tara Smith, an assistant professor in the epidemiology department at the University of Iowa, said Warner’s argument ignored the fact that scientists are able to draw reasonable conclusions regarding human health risk based on the bacteria populations found in animals and humans.
A 2004 Government Accountability Office report summarizing the scientific evidence on the transfer of antibiotic resistance from animals to humans explained that “some studies have provided evidence of associations between changes in antibiotic use in animals and resistance to antibiotics in humans,” and that “studies that have examined the genetic makeup of the bacteria have provided evidence of a stronger link and have established that antibiotic-resistant campylobacter and salmonella bacteria are transferred from animals to humans.”
The report went on to note that a “small number of studies contend that health risks of the transference are minimal,” but pointed out that there are “many studies that have examined the genetic makeup of the bacteria [that] have provided evidence of a stronger link and have established that antibiotic-resistant campylobacter and salmonella bacteria are transferred from animals to humans.”
Warner said the scientific evidence did not demonstrate how the pork industry’s antibiotic use contributed to antibiotic resistance in humans. “We have never said that we are no part of the problem of antibiotic resistance,” he said. “We don’t know what, if any, part we are.”
Given the substantial risks antibiotic-resistant bacteria pose to public health, however, would it not be better to err on the side of caution in case the industry is making the problem worse?
Warner would not contemplate that circumstance, instead repeatedly reciting a different “what if” (that is, if, contrary to all scientific expectations to date, a consensus were to emerge that there is absolutely no link between industry practice and human health hazard, after the industry had been restricted). Banning the non-therapeutic use of antibiotics in animals would be costly to producers, he said.