A mathematical model of antibiotic resistance gene flow from livestock and spread amongst humans

The evolution and spread of antibiotic resistance poses a major threat to human health. The high level of antibiotic use in the rearing of livestock is contributing to the origin and persistence of antibiotic resistance amongst humans. Understanding how resistance genes spread from livestock to humans and investigating the impact of managing antibiotic use in livestock will be important for guiding strategies to reduce the risk to humans. We have developed a mathematical model of the transmission of resistance genes from livestock to humans and their spread amongst the human population. Using this framework we demonstrate that although resistant zoonotic foodborne infections do not contribute significantly to the annual burden of death, they could be a source of resistance amongst other pathogens, including those that exclusively spread between humans. Amongst these pathogens, only livestock-derived resistant strains that are associated with a net fitness cost would be expected to decline in prevalence following control strategies aimed at reducing the impact on humans of antibiotic use in livestock. Author SummaryAntibiotics are an essential component of human health care. They are also used in the rearing of livestock for human consumption, which contributes to the development of antibiotic resistant pathogens. Although humans are known to be at risk from antibiotic resistance that evolves amongst livestock, the number of human lives that are at stake remains unclear. Furthermore, the number of lives that could be saved through interventions to reduce antibiotic use in livestock has not been evaluated. Here, we have developed a mathematical framework to explore these questions. Using this framework we explicitly demonstrate that there are too many uncertainties to calculate the number of preventable human deaths. Nevertheless, the importance of reserving new and currently effective antibiotics for human use is clear. Once resistance genes that do not have a fitness disadvantage have spread from livestock to humans, it is too late for interventions targeted at livestock to affect their prevalence in humans in the long term.