Food chain’s new links

Dr Cliodhna Foley Nolan on the relationship between antibiotics in animal feed and AMR in humans.
We have tended to associate antimicrobial resistance (usually antibiotic resistance) with overcrowded hospitals, poor hand-washing and over-prescribing by medical clinicians. However, it is clear that there is also a causal relationship between antimicrobial use in food, animals and human illness.

While use of antibiotics as growth promoters has been banned since 2005 in the EU, antibiotics can still be added to feed and water to control respiratory and enteric disease in food-producing animals. This poses minimal risk to the animals, but is now recognised to contribute to the burden of antimicrobial resistance (AMR) in humans. AMR in animal reservoirs can subsequently compromise treatment effectiveness for human infections.
The WHO in 2008 and the World Organisation for Animal Health (OIE 2003) have concluded that non-human usage poses adverse consequences for human health. When bacteria are exposed to antibiotics, it automatically forces selection for antibiotic-resistant strains. Since 70 per cent of all human pathogens are shared with animals, exchange of AMR bacteria between humans and animals is inevitable.
Many classes of antibiotics are currently used in both human and animal therapy. This poses risks for the development of resistance and its transfer to humans. The transfer can occur by direct contact with animals, shared environments such as slurry leaking into ground water or through meat. Even commensal bacteria can acquire and disseminate gene-based AMR.
h4. Monitoring AMR
Surveillance of human pathogens in Ireland reveals clear evidence of increasing prevalence of multi-drug resistant (MDR) Salmonellae, Coliforms, Campylobacter and S. aureus, typified by MRSA.
In Ireland, the European Antimicrobial Resistance Surveillance System (EARSS) provides information from 43 Irish laboratories on seven infections. This is epidemiologically analysed. However, outside of this scheme, there are gaps in nationally co-ordinated surveillance for other pathogens and their AMR profiles. Research findings in animals in Ireland also show that AMR, and indeed multi-drug resistant isolates, are present in poultry, pigs and cattle. Currently, no routine AMR surveillance such as EARSS exists for animals.
Compilation of national trends for pathogens and AMR is limited by the lack of standardisation of laboratory procedures, reference laboratories and analysis of data produced.
h4. Antibiotic usage
Monitoring of antimicrobial (AM) usage is essential. Identification of AMR patterns is only half the picture. Levels of antimicrobial prescribing must be correlated with trends in AMR pathogenic bacteria.
A centralised animal and human AMR database would be a progressive step in the integrated monitoring (such as the DANMAP system in Denmark). Integrated AMR monitoring, with antimicrobial consumption data, would allow for the investigation of associations between antimicrobial usage and resistance. Routes of transmission might be identified.
h4. The challenge
In underdeveloped countries, increasing AMR is linked with poverty, the purchase of cheap substandard antibiotics and self-medication, further complicating the problem. Different prescribing and usage patterns exist for animals compared to people. On large modern farms, antibiotic usage is best reduced through the use of Veterinary Herd Health Programmes focused on improved biosecurity, vaccination programmes and targeted use of antimicrobials where necessary.
Recent research has shown that Irish veterinary prescribing practices are based on client expectations, costs and clinical experience. Vets in private practice report difficulties in persuading farmers to change from herd-based antibiotic medication to disease-reduction control programmes.
Obstacles to the change include farmer-targeted advertising, especially over the internet, promoting the prophylactic use of antibiotics as a legitimate first line of defence in disease control.
In addition to public health implications, the food industry has commercial concerns should AMR pathogens be found to survive processing and cause illness. A costly loss of consumer confidence is a genuine concern.
We know that infections caused by resistant organisms have certain human health consequences including treatment failures, increased severity of infection and associated morbidity and mortalities. A list of antimicrobial drugs used in human and veterinary medicine have now been classified as ‘critically important’, ‘highly important’ and ‘important’, based on how essential they are for human medicine (WHO 2005, 2007).
Thus, the use of certain antimicrobials is banned or restricted in food animal veterinary practice in an effort to stem the emergence of AMR.
The Veterinary Council of Ireland has guidelines on ethical veterinary practice for the profession that require them to use best practice when prescribing medicines including antimicrobials.
Safefood funded a meeting in December 2008 of veterinary and medical experts to consider human AMR as a condition that can be transmitted from food animals to humans on the island of Ireland.
This issue poses an ongoing challenge and a call for collective efforts of both medical and veterinary experts. It presents another aspect of antimicrobial resistance to add to the already complex mix.
* Dr Cliodhna Foley Nolan, Director, Human Health and Nutrition, Safefood.