ANTIMICROBIAL RESISTANCE (AMR)

The discovery of antibiotics was one of the key medical achievements of the 20th century. Yet, less than 100 years after Alexander Fleming first discovered penicillin, the world is on the cusp of a post-antibiotic era, with multi-resistant strains of bacteria emerging at alarming rates all around the world. The United Nations has declared antimicrobial resistance (AMR) a global health risk, stressing that deaths due to AMR could soon surpass annual cancer fatalities.1 Globally, antimicrobial-resistant infections currently claim at least 700,000 lives each year. This number could reach an annual toll of 10 million by 2050.2 3 Common bacterial infections that used to be easily treatable with the aid of antibiotics can now be fatal – again! This is not only a problem for individual and public health in and of itself, with AMR having become one of hospitals’ biggest challenges.4 It also renders affected individuals even more vulnerable to novel pathogens and adds to the massive strain on healthcare systems during a pandemic.

Animal agriculture – the unrecognised driver of AMR

While there is growing awareness of the challenge of AMR, little is known about the driving force behind it. Animal agriculture is chiefly responsible for the development of AMR. Globally, more than 70% of antibiotics are used on animals in intensive farming – to prevent losses owing to the problematic breeding and husbandry conditions, and to accelerate growth and profits – rather than for the treatment of humans.5 Yet, the main focus when tackling antimicrobial resistance is usually on the importance of doctors prescribing antibiotics appropriately, rather than on their large-scale misuse in animal agriculture.

AMR in pandemics – a profound risk multiplier

Although antibiotics are not able to kill or inhibit viruses, their declining efficacy in treating bacterial pathogens aggravates the overall health risk for humans and increases the burden on healthcare systems.6 They are essential in fighting bacterial infections which may accompany a primary viral infection. Lower and upper respiratory infections are the fourth-highest cause of global mortality and are usually caused by a virus.7 However, additional secondary bacterial infections are common complications, increasing the severity of a viral infection and further raising the morbidity and mortality rates of viral diseases.8 When antibiotics are effective and readily available, this risk decreases. However, with more and more strains of antimicrobial-resistant bacteria emerging, AMR can further escalate an epidemic or a pandemic. In the case of influenza, for instance, bacterial infections are assumed to contribute to up to 50% of total deaths.9 10 11 During the 2009 swine influenza pandemic, cases of secondary bacterial infections increased, causing up to 55% of total deaths.12 This makes AMR a massive risk in and of itself – as well as a profound risk multiplier in the context of a zoonotic pandemic.

Towards a post-antibiotic era

Research on the 1918 influenza pandemic revealed that secondary bacterial infections might have been the main cause of death, probably responsible for up to 90% of fatalities.13 This happened in the pre-antibiotic era, when the treatment of bacterial infections was still a challenge. With more and more antibiotic-resistant bacteria, and AMR increasingly posing a global health risk again, we are now headed for a post-antibiotic era. Without effective treatment for secondary bacterial infections, future pandemics are poised to get worse, leaving health professionals helpless against a threat we thought we had overcome.

Animals, humans, and AMR

While physicians and patients are supposed to follow strict antibiotic prescription guidelines in order to prevent AMR, that advice again misses the elephant in the room: globally, more than 70% of antibiotics are not used for the treatment of humans but for animals in intensive farming setups.14 The key problem here is the overlap: 76% of the antibiotics commonly used in agriculture and aquaculture are also important in human medicine15 – with the animal-usage dramatically decreasing the efficacy of antibiotics intended for humans.

Preventing losses and accelerating growth in factory farms – a recipe for AMR emergence

Animal farming is the main consumer of antimicrobial medicines due to its problematic breeding and husbandry conditions. Farmed animals suffer physically from impaired immune systems, weaker bones or cardiovascular systems, and bodily mutilations, as well as from genetic predisposition to various injuries and diseases.20 They also experience mental suffering due to a range of causes, including stress, the inability to display normal behaviour, and severely restricted movements due to overcrowding or otherwise unsuitable husbandry,21 as well as from unhygienic conditions.22 23 This makes the animals more vulnerable to infectious diseases. In intensive-farming facilities, outbreaks are more common and harder to control when they occur.24 25

In order to prevent excessive losses of animals – and thus profit – a seemingly ‘easy’ solution is the extensive use of antibiotics. This is why antibiotics are routinely given, for example, to sows who are kept continuously impregnated, except for a few weeks after giving birth, or to young pigs in order to reduce disease symptoms caused by stressful early weaning.26 Antibiotics are also administered to poultry to combat heat stress, overcrowding, and other substandard living conditions.27

The majority of animals are treated with antimicrobial medicine as a preventive measure. However, antibiotics are not administered to animals only for disease control. Some of these drugs also induce growth and weight increase in animals – a welcome side-effect for the animal-farming industry, as it reduces the timespan needed for animals to reach their slaughter weight or increase it. Unsurprisingly, this has led to very generous use of these drugs.28 29 And, while regulatory efforts have attempted to curb such misuse of vital antibiotics, in reality, they have mostly failed.30

Wasting powerful drugs on animal agriculture – including antibiotics of ‘last resort’

Two of the most commonly used antibiotics in animal agriculture are tetracyclines and fluoroquinolones, both of which are also used to treat various severe illnesses in humans, including cholera and malaria.31 32 Resistance to tetracyclines has already been detected in industrial poultry farming.33 34 And the use of fluoroquinolones also poses a public health concern as they are suspected of encouraging bacterial resistance, which can be transmitted into the food chain.35 The misuse of antibiotics in animal agriculture also extends to drugs of ‘last resort’ – that is, antibiotics which are used as a last line of defence for humans whose infections are failing to respond to standard drugs. Life-saving medicines for humans, such as colistin, are wasted, mostly on healthy animals in order to boost their growth and weight, or to prevent them from contracting infectious diseases resulting from inadequate husbandry conditions.36 37 Colistin is used in the treatment of E. coli infections (see 3.2) but also to treat pneumonia. Resistance to colistin has been detected around the world38 with nearly 100% of farmed animals in some regions – as well as a rising number of people – carrying the resistant gene.39 Since colistin is a valuable drug that is used to treat multi-resistant bacteria, this development poses a serious and growing global threat.40

Factory farms and aquaculture – breeding grounds for dangerous superbugs

There is a strong link between the intensive use of antibiotics in animal farming and the rapid emergence of new resistant bacteria, leading to a record level of superbugs in various domesticated animal species.41 42 43 44 (Superbugs are microorganisms that have developed multi-drug resistance.) This holds particularly true for the clear increase in resistant bacterial strains occurring in chickens and pigs.45 46 47 Globally, the production of animal-based products is estimated to increase by 15% by 2028.48 This increase in meat, milk, and egg production also implies a rise in antibiotics use in animal farming, which is projected to rise by 67% by 203049 – with some countries expected to see an up-to-80% increase.50 Global AMR maps (available at resistancebank.org and ourworldindata.org)51 52 show that the countries with the highest resistance rates are also the countries that have the highest use of antimicrobials commonly used by humans also used in animal farming.53 54

The indiscriminate use of antibiotics makes the aquaculture sector another hazardous breeding ground for AMR55 – and one that deserves special attention, since aquaculture is one of the fastest-growing food-production sectors worldwide.56 Global fish production rose to about 171 million tons in 2016, with aquaculture constituting 47% of the total.57 As aquaculture intensifies in order to meet global demand, so too do the diseases and pathogens affecting aquatic animals.58 59 The intensification of aquaculture enables an ideal setting for rapid changes in pathogen populations, genetic exchange, and recombination to take place. All of these factors have long-lasting evolutionary effects on pathogen virulence and outbreaks.60 61 Furthermore, many countries practice an integrated agriculture-aquaculture farming system in which aquaculture is sustained via livestock and human waste, maximising the exposure of animals, humans, and the environment to AMR.62 63

Animal-agricultural waste and the spread of AMR

Factory farms produce large quantities of waste, which, in most cases, is disposed of in nearby areas.64 This increases the risk of the transfer of AMR genes to farmed animals, humans, wildlife, and watersheds.65 66 Antibiotics not only pose a direct threat to overall human health but also have an impact on the environment. Most of the antibiotics are excreted and disseminated into the environment via run-off water or manure used as fertiliser, after which they get into rivers, lakes, and groundwater used for human consumption, as well as into our soils. In this way, they potentially alter the microbial community and cause the emergence of new resistant strains.67 68

Animal-agriculture workers and the spread of AMR

Factory farms enable frequent and close contact between animals and people who work on or live close to the farms. Methicillin-resistant Staphylococcus aureus (MRSA) is a clinically significant superbug that causes infections of the respiratory system worldwide. In Germany alone, there are about 132,000 cases of MRSA each year. MRSA is widespread in various different species of farmed animals and is easily transmitted to humans who are in direct contact with them.69 In German regions with high numbers of farmed animals, 86% of hospital-admitted MRSA cases are farmers, and more than 4% are farmers’ relatives.70

AMR – the superbugs we grow in our farms

Instead of using antibiotics to keep humans healthy, our current food system wastes these valuable drugs in order to maintain the lives of animals who would otherwise not be viable under the circumstances they are kept in – all in order to produce large amounts of cheap animal-based products. As a consequence of the ever-increasing global demand for animal-based products, the unabated growth of antimicrobial resistance is particularly alarming, since the massive misuse of antimicrobial drugs increases the risk of the impacts of pandemics becoming even more severe. 

The current model of animal agriculture not only enables and encourages viral evolution and transmission, but also increases antimicrobial resistance. This alarming combination poses a threat to human health everywhere, regardless of whether people eat the animals raised under those conditions or not. 

In terms of the increase in antibiotic resistance, there is a further connection with our animal-based food system and what we eat: many microorganisms that have developed antimicrobial resistance are also involved in food-borne diseases. These include Salmonella, Clostridium, Campylobacter, Staphylococcus, Escherichia coli (E. coli), and Listeria. Crucially, they all have meat or dairy as their main sources.85 86