David G S Burch
BVetMed DECPHM MRCVS
Veterinarian, Octagon Services Ltd
The prudent and rational use of antimicrobials in animal health is controlling the development of resistance in animals, and the relatively small risk of resistance transfer to man. The medical side has their own problems.
The recent report by the Veterinary Medicines Directorate (VMD) (2008) has shown that there has been a 4.4% reduction in therapeutic antimicrobial use in animals over the last year and nearly a 14.8% reduction over the last three years. If we look at pig and poultry use, which is separated out then it has fallen 6.8% since the previous year and 15.7% over the last three years. Is this a time bomb ticking away - the overall figures suggest it is not.
The use of antimicrobials, which are on the WHO 'critical list' such as cephalosporins and fluoroquinolones have indeed increased. However, in which sector has the increase occurred, unfortunately the report does not specify or if they are the 3rd and 4th generation more advanced cephalosporins, which the WHO is concerned about. If we look at other countries usage patterns such as Scandinavia and France, where recently they have been reported by the European Medicines Agency (EMEA) (2008), 69% of cephalosporins are used in pet animals (dogs and cats - a growing market in the UK), 16% are used in dairy cows to treat and control mastitis and 15% are used in cattle and pigs for the treatment primarily of respiratory infections such as pneumonia, by injection only. There are no oral forms (feed premixes or water solubles) of cephalosporins of any generation licensed for use in cattle and pigs in the UK. In an earlier report VMD (2007) showed that the consumption of cephalosporins in man was 39.8 tons and in animals 3 tons, a ratio of 13.3:1. If we then divide it further into cattle and pig use the ratio increases to 88.4:1. An additional section of the EMEA document reports on a survey of Escherichia coli, used as an indicator organism for antimicrobial resistance, from poultry and pigs and showed that there was no resistance to 3rd generation cephalosporins in the UK. They also reported on Salmonella species from cattle, poultry and pigs and S. Typhimurium from cattle and pigs and again showed no evidence of 3rd generation cephalosporin resistance.
For the fluoroquinolones, the picture of usage is less distinct. However, VMD (2007) reported that in humans quinolone use was 14.7 tons and in animals only 1 ton a ratio of 14:1. It is hard to break it down further into different species use but use in pet animals is also significant but probably not as large as in food-producing animals, unlike the cephalosporins. Oral formulations are available as well as injectable formulations in food-producing animals. In the Veterinary Laboratories Agency (2007) annual survey for 2006 of Salmonella spp (4331 isolates from food producing animals) there was only one isolate resistant to ciprofloxacin (the human test fluoroquinolone) from poultry (0.02% of isolates) and none that were resistant to the 3rd generation cephalosporins, cefotaxime and ceftazidime directly used in human medicine.
Yes, the EMEA, VMD and our own Pig Veterinary Society (PVS) warns its members to use antimicrobials prudently, and on the results so far, they appear to have done a good job in taking this advice and preserving the safety of our food in the UK.
EMEA (2008) 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. EMEA/CVMP/SAGAM/81730/2006-CONSULTATION (18TH February 2008)
VLA (2007) Salmonella in livestock production in GB - 2006.
VMD (2007) Overview of antimicrobial usage and bacterial resistance in selected human and animal pathogens in the UK: 2004
VMD (2008) Sales of antimicrobial products for use as veterinary medicines antiprotozoals, antifungals, growth promoters and coccidiostats in the UK in 2007.
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