Global health authorities are discouraging use of antimicrobials in food-producing animals in the absence of disease.
World Health Organization guidelines published in November 2017 state that livestock industries should stop using antimicrobials to prevent disease or improve production in livestock. They also advocate reducing overall antimicrobial administration to livestock, especially administration of drugs important for human medicine.
The WHO also is recommending veterinarian oversight of antimicrobial use in food-producing animals, use of antimicrobial resistance tests in treatment decision-making, use of vaccines and sanitation to prevent disease, and limitation of some classes of antimicrobials to use in human medicine.
Marc Sprenger, MD, director of the WHO antimicrobial resistance secretariat, said in a press conference that antimicrobial resistance is causing untreatable infections and a substantial public health threat. Overuse and misuse of antimicrobials in humans and animals have been important causes of resistance.
Kazuaki Miyagishima, MD, the WHO's director of food safety and zoonoses, said prolonged or routine antimicrobial use promotes antimicrobial resistance and that reducing overuse in animal production is necessary to protect public health.
Dr. Miyagishima said antimicrobials should not be used for production or as preventive measures in the absence of animal disease, with potential exceptions for prevention uses under veterinarian oversight. The WHO also recommends taking samples from animals to determine which antimicrobials are effective and using the most likely effective antimicrobials that are least important for human medicine.
The guidelines published in November were developed through the organization's stringent guideline development process, which includes systematic reviews, he said.
U.S. Department of Agriculture acting chief scientist Chavonda Jacobs-Young, PhD, said in an announcement that the WHO guidelines on antimicrobial use in animals lack support from "sound science." She said the recommendations conflate disease prevention and growth promotion.
Dr. Jacobs-Young notes that the guidelines indicate the WHO's recommendations are based on "low quality evidence."
The recommendations to reduce overall antimicrobial use in food-producing animals and restrict growth promotion and disease prevention uses include notes of "strong recommendation, low quality evidence." The recommendations of limiting or preventing antimicrobial administration to food-producing animals on the basis of the antimicrobial's importance in human medicine include notes of "conditional recommendation, very low quality evidence."
The WHO guidelines indicate the organization assessed its own recommendations using a grading system that is designed to assess clinical and public health interventions and assigns initial ratings of "low quality" to all studies that are not randomized control trials. The body of evidence for the recommendations was bound to have low ratings under that system.
"It is not practical, and in some cases not ethical, to conduct randomized clinical trials to investigate the impact of restricting antimicrobial use in food-producing animals on the prevalence of antimicrobial resistance," the guidelines state.
Adapting the grading system to address complex questions involving environmental exposures and interventions is challenging, the guidelines state.
The document also states that the WHO guideline development group concluded that the potential human health benefits of lowering the prevalence of antimicrobial resistance in humans outweighs any potential harm or unintended negative consequences of limiting antimicrobial use. The evidence for the recommendations comes from review of substantial information supporting the assertion, it states.