In August the World Health Organization went on record as favoring a worldwide ban on the use of growth-promoting antibiotics in animal feed. Routine use of animal antibiotics to promote growth is controversial due to fears that it might increase the rate at which human diseases become antibiotic resistant.
WHO cites the example of Denmark which banned the use of growth-promoting antibiotics in animal feed. According to WHO, the result was an increased cost to farmers of one percent, but was more than justified by the large decline in antibiotic resistant bacteria found in pigs and chickens — in some cases the level of antibiotic resistant bacteria fell from 80 percent before to 5 percent after the ban.
But, the WHO concedes it is still missing the crucial piece of the puzzle — does reducing antibiotics in animals reduce antibiotic-resistant diseases in human beings. There, the WHO concedes that there is no evidence that the ban on animal antibiotics in feed has had any positive effect on human health,
Data from healthy humans however are relatively sparse on which to assess the effect of the termination of antimicrobial growth promoters on the carriage of antimicrobial resistant bacteria. There is some indication that termination of antimicrobial growth promoters in Denmark may be associated with a decline in the prevalence of streptogramin resistance among E. faecium from humans. There is also an indication that the termination may be associated with an increase in resistance among E. faecalis to erythromycin (a macrolide), which may reflect an increase in the therapeutic use in pigs of tylosin (another macrolide). However, it should be noted that erythromycin is not a very important antimicrobial for the treatment of enterococcal infections in humans; preferred drugs include ampicillin, amoxycillin, vancomycin, streptogramins (for E. faecium), and linezolid. Further larger studies are needed to determine how much of an effect the discontinued use of antimicrobial growth promoters in Denmark will have on the carriage of antimicrobial resistance in the intestinal tract of humans in the community.
. . .
Overall, termination of antimicrobial growth promoters appears not to have affected the incidence of antimicrobial residues in foods or the incidence of human Salmonella, Campylobacter, or Yersinia infections in humans. These are the major zoonoses in Denmark that may be associated with consumption of pork and poultry. In an industry aggressively pursuing successful Salmonella reduction strategies, antimicrobial growth promoter termination appears not to have affected the prevalence of Salmonella in pig herds, pork, broiler flocks and poultry meat, or the prevalence of Campylobacter in poultry meat.
WHO and others are likely going to have to come up with a bit more positive results than that before seeing other nations emulate Denmark’s experiment.
Sources:
WHO Urges End to Use of Antibiotics for Animal Growth. Marc Kauffman, Washington Post, August 12, 2003.
WHO warns farmers on antibiotics. Associated Press, August 13, 2003.
Cut down on drugs for animals: UN agency. CBC News, August 13, 2003.
WHO international review panel’s evaluation of the termination of the use of antimicrobial growth promoters in Denmark. World Health Organization, August 2003.