Monitoring and better understanding the spread of antimicrobial resistance in animals: key points from the latest ANSES reports

Resapath's observations: the decline in antimicrobial resistance continues

Since 2001, the French surveillance network for antimicrobial resistance in pathogenic bacteria of animal origin (Resapath) has monitored the spread of bacteria that are resistant to antibiotics, including those of critical importance to humans, in populations of sick farm animals and pets. A network of 71 veterinary testing laboratories is tasked with detecting these bacteria. During 2019, they carried out 53,469 tests. Escherichia coli was the main bacterial species identified and is the primary indicator for monitoring trends in antimicrobial resistance.

In general, there has been a decrease or stabilisation in the levels of resistant bacteria. Specifically, for the E. coli bacterium:

• resistance to two classes of antibiotics, third- and fourth-generation cephalosporins and fluoroquinolones, is monitored particularly closely as these are crucial for human health and have few or no alternatives. For these two classes of antibiotics, the proportion of resistant bacteria is low and the downward trend observed in recent years is continuing: levels of cephalosporin-resistant bacteria range from 1% in pigs and poultry to 4% in cats. Proportions of fluoroquinolone-resistant bacteria range from 3% for pigs, turkeys and horses to 8% for cattle;
• colistin is another antibiotic that is closely monitored. Resistance to this antibiotic has been under control for the last 15 years and concerns fewer and fewer strains of bacteria;
• for other antibiotics, the general trend is a slight decrease or stabilisation in resistance. The situation varies according to the sector: poultry, for which a very sharp decrease in antimicrobial resistance had been observed before 2014, have the lowest levels of antimicrobial-resistant bacteria: this level is no higher than 30% in hens and chickens for the antibiotics responsible for the most resistance, and it is a maximum of 40% for turkeys. The fall in antimicrobial resistance has been less pronounced in pigs and the situation is stable for cattle: the highest levels of resistant bacteria are 65% in pigs and 75% in cattle;
• multidrug-resistant bacteria, i.e. those that are non-susceptible to more than three antibiotics, are declining in all sectors. In 2019, the proportion of multidrug-resistant strains was highest in cattle, with 15.5% multidrug-resistant bacteria, and lowest in turkeys (2%).

In addition, resistance to methicillin, another major indicator of antimicrobial resistance, mainly concerned the bacterium Staphylococcus pseudintermedius, a staphylococcus species responsible for disease in domestic carnivores. This resistance was present in 15-20% of the strains tested, a phenomenon comparable to that observed in humans for Staphylococcus aureus. Note that S. pseudintermedius only very rarely affects humans.

Monitoring of the use of veterinary medicinal products: animals generally less exposed to antibiotics  

Through the French Agency for Veterinary Medicinal Products (ANSES-ANMV), ANSES monitors sales of veterinary antibiotics and animal exposure to them. It does this based on sales of veterinary medicinal products reported by the marketing authorisation holders. The quantity of antibiotics sold is steadily decreasing, with 422 tonnes of antibiotics sold in 2019, 10.5% less than in 2018.
However, the tonnage of antibiotics sold does not reflect actual exposure of animals to antibiotics, as this depends on the dosage of the drug, the duration of administration and changes in the populations of the different animal species considered. The Agency took into account the recommendations for use of the drugs studied and the estimated weights of the animal populations, to determine the level of exposure of animals to antibiotics.

Main results:

• the exposure level was the lowest since monitoring began in 1999. Compared to 2011, the reference year of the first EcoAntibio plan, which aimed to reduce antibiotic use by 25% in five years, exposure to antibiotics for all animal species combined has fallen by 45.3%;
• this decrease continued in 2019, with an overall reduction of 10.9% compared to the previous year;
• this trend varied according to species: exposure has decreased in cattle, pigs and poultry, which have seen falls of 9.9%, 16.4% and 12.8% respectively in one year, whereas a slight rebound was observed in 2019 for rabbits and domestic carnivores (dogs and cats): +1.5% for rabbits and +2.1% for carnivores. This uptick should not overshadow the downward trend observed since 2011;
• exposure of animals to critically important antibiotics has fallen sharply since 2013, and has stabilised in the last three years: between 2013 and 2019, it decreased by 86% for fluoroquinolones and by 94.1% for newer-generation cephalosporins;
• colistin, for which transferable resistance mechanisms have been reported, has seen its exposure rate fall by 64.2% from the reference average level between 2014 and 2015. The target of a 50% reduction in five years set by the second EcoAntibio plan for 2017 has been achieved for the pig, poultry and cattle sectors.

In conclusion, the push to encourage the prudent and responsible use of antibiotics in recent years has been a success, which needs to be sustained by the continued efforts of all stakeholders.