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Could antibiotics routinely added to animal feed be a contributing factor to the raising levels of antibiotic resistance in human diseases?

David Wallinga from Keep Antibiotics Working: the Campaign to End Antibiotic Overuse in Animal Agriculture told the BMJ online that he thinks that the use of antibiotics in livestock has a "critical role" in the resistance levels to the drugs in humans.

He believes that physicians and policy makers have overlooked this theory, and advises the relevant parties to consider it before developing new, stronger antibiotics.

Overall reductions in antibiotic use should come before any new development, he says. In 2009-11, 72 per cent of the US sales of antimicrobials were intended for water or animal feed for livestock.

Around the world, diseases which were treatable using antibiotics have now become resistant, with the number of patients admitted to hospital for these illnesses sky rocketing. In the case of Clostridium difficile (C difficile), a species of bacteria that causes severe stomach problems, admissions have doubled and deaths tripled.

Wallinga does not believe that routine antibiotics are necessary to the health of livestock and poultry. He cites Denmark, the world's leading pork exporter, which has reduced the amount of antimicrobial used in livestock farming and simultaneously increased its pork production by half.

He states that based on evidence, almost every European and North American public health authority agrees that the use of antibiotics in animal feed has likely had a negative effect on disease resistance, but "less certain is the political will to act upon that information".

However, there are some who disagree with Wallinga's claims. Veterinarian David Burch commented that there is no more risk of resistance from eating meat from medicated animals than an orally administered antimicrobial on a human.

He argues, "it is considered highly unlikely that the use of adding antibiotics to feed poses a serious risk to humans, especially in comparison with the extensive use of antibiotics directly in human patients".