24-06-2009 - Use of antimicrobials
Use of antimicrobialsRichard Young1
1 Soil Association, South Plaza, Marlborough Street, Bristol BS1 3NX
Dai Grove-White and Richard Murray are right to express concern about the use of cephalosporins and fluoroquinolones in farm animals (VR, June 6, 2009, vol 164, p 727), but do we really need a ban, as they argue?
Between 1999 and 2006, veterinary use of third and fourth generation cephalosporins in the UK tripled from 220 kg to 680 kg active ingredient (VMD, personal communication). Fluoroquinolone use fell in 1999, but rose from 1230 kg in 2000 to 1951 kg in 2007 (VMD 2006, 2008).
Why is this happening? In my experience, most large animal veterinary surgeons would prefer to hold these highly effective drugs in reserve. However, this is not quite universally the case. Advertisements targeting farmers have also created a demand with little to counterbalance it, especially in relation to modern cephalosporins, where the manufacturers still suggest that the chance of resistance developing in foodborne bacteria is low (EMEA 2007, Intervet 2009).
Over the past decade there has been a dramatic increase in urinary tract and blood poisoning infections in humans caused by extended-spectrum β-lactamase (ESBL) resistant strains of Escherichia coli, which are resistant to cephalosporins and frequently to fluoroquinolones. According to the VLA, these may initially have passed to farm animals from humans, perhaps due to spreading sewage sludge on agricultural land (VR, October 27, 2007, vol 161, p 576), but they are now being selected for and amplified in farm animals (CVMP 2009), particularly by the use of these drugs (Cavaco and others 2008). While there is no conclusive proof, there is mounting evidence that farm animals have become an important reservoir for human infections and ESBL-resistance plasmids (Coque and others 2008). A precautionary approach is therefore needed.
The use of ceftiofur in pigs (datasheet and off-label) and cattle (CVMP 2009) and cefquinome in cattle have been implicated in the emergence of ESBL resistance, in dairy calves possibly due to feeding milk during the withdrawal period (CVMP 2009). Data published in the 2006 EU zoonoses report for the UK show that cefotaxime/ceftiofur resistance in E coli in cattle increased to 7·5 per cent in 2006 (EFSA 2008).
The Soil Association seeks to limit the development of antimicrobial resistance on the approximately 2000 organic livestock farms it certifies through limitations on the use of all antimicrobials and strong emphasis on systems design. We introduced additional restrictions on the use of fluoroquinolones in 2004 and extended-spectrum cephalosporins on January 1 this year; however, we decided against a ban to avoid occasional treatment failures and associated welfare problems.
We now require our livestock farming licensees to discuss the use of these antibiotic classes with their vet and record the conclusions in annual health plans. We realise there could be teething problems, but hope the profession will work with us in a constructive way to limit their use on our organic farms at least to second- or third-line treatments in individual animals, or very occasional situations where it is known that no alternative antibiotic would be effective.
CAVACO, L. M., ABATIH, E., AARESTRUP, F. M. & GUARDABASSI, L. (2008) Selection and persistence of CTX-M-producing Escherichia coli in the intestinal flora of pigs treated with amoxicillin, ceftiofur, or cefquinome. Antimicrobial Agents and Chemotherapy 52,3612 -3616[Abstract/Free Full Text]
COQUE, T. M., BAQUERO, F. & CANTON, R. (2008) Increasing prevalence of ESBL-producing Enterobacteriaceae in Europe. Eurosurveillance 13,1 -10
CVMP (2009) Revised reflection paper on the use of 3rd and 4th generation cephalosporins in food producing animals in the European Union: development of resistance and impact on human and animal health. Committee for Medicinal Products for Veterinary Use. www.emea.europa.eu/pdfs/vet/sagam/8173006enfin.pdf. Accessed June 15, 2009
EFSA (2008) United Kingdom. Trends and sources of zoonoses and zoonotic agents in humans, foodstuffs, animals and feedingstuffs in 2006. www.efsa.europa.eu/EFSA/DocumentSet/Report_2006_United%20_Kingdoms.pdf?ssbinary=true. Accessed June 15, 2009
EMEA (2007) European Public Assessment Report. Naxcel. Scientific discussion. www.emea.europa.eu/vetdocs/PDFs/EPAR/naxcel/16824605en6.pdf. Accessed June 16, 2009
INTERVET (2009) Cobactan 2.5 % suspension for injection.www.cobactan.com/Product-Cobactan.asp. Accessed June 16, 2009
VMD (2006) Sales of antimicrobial products authorised for use as veterinary medicines, antiprotozoals, antifungals, growth promoters and coccidiostats in the UK in 2005. Veterinary Medicines Directorate. www.vmd.gov.uk/Publications/Antibiotic/salesanti05.pdf. Accessed June 15, 2009
VMD (2008) Sales of antimicrobial products authorised for use as veterinary medicines, antiprotozoals, antifungals, growth promoters and coccidiostats in the UK in 2007. Veterinary Medicines Directorate. www.vmd.gov.uk/Publications/Antibiotic/salesanti07.pdf. Accessed June 15, 2009