Written by Hafsah Ganatra and Edited by Ashima Seth
Whether it is to treat an infection, disease, or illness, antibiotics are often seen as a reasonable solution to an otherwise potentially harmful problem. Yet, when we think about the patients using these antibiotics, very rarely do we imagine animals. Surprisingly though, approximately 80% of all yearly antibiotic usage is sourced from animal agriculture [1]. While antibiotics are constantly being produced for human use against infections, many of these medicinal products are instead used on animal livestock. The use of antibiotics on animals such as cows, chicken, and pigs is actually widespread amongst livestock farmers. In fact, around 18.6 million pounds of antibiotics were sold for animal use in 2016 alone [2].
Much like in humans, these antibiotics can be used to treat infectious illnesses in animals [3]. Diseases within animals often spread fairly quickly, especially when considering the closely quartered living conditions of livestock, which can easily lead to the excessive need for antibiotics. Currently, the most frequent applications of antibiotics on livestock rely mainly on prophylactic, or preventative, use while maintaining varying degrees of function [4]. For example, almost all dairy cows are injected with drugs to prevent the development of any infections in the udder tissue or mammary glands. Meanwhile, other injections are given to both infected and healthy cows in efforts to treat and prevent lung infection and respiratory diseases [3]. Beyond its healing functions, US farmers would often utilize antibiotics to promote the growth of livestock for a better harvest in a practice that has since been banned by the United States’ Food and Drug Administration in 2017 [5].
The main cause of concern for many researchers regarding this use of antibiotics on animals is the expansion of bacterial resistance, which can be promoted following excessive antibiotic use. Bacteria are constantly evolving, and as antibiotics are applied more and more vigorously, the bacteria can grow increasingly tolerant of certain antibiotics, eventually leading to developments of entirely resistant bacterial populations. This is similar to the process in which our sense of smell adapts a tolerance to repulsive odors after prolonged or repeated exposure. So, the question remains: how does this affect humans? Many scientists are currently researching the potential impact that bacterial resistance within livestock can have on human individuals with the current, and seemingly endless, extension of the meat industry.
For now, scientists have identified three potential higher-risk areas of impact for humans: the transmission of a bacterial infection through infected animals, the possibility of animal-borne viruses crossing over to affect humans, and the transference of bacterial resistance through associated genes via methods like phage transduction which is when a virus transfers DNA between different organisms [1]. While cases of each impact have been observed over time, the most common and easily discernible is the transfer of animal-borne viruses like rabies or the plague, infecting humans and eventually leading to widespread illness. It is also estimated that greater degrees of bacterial infections are being transmitted to humans through infected meats and contamination caused by abundant antibiotic use. However, this transfer does not result in direct human affliction and thus is not as apparent [1]. Nevertheless, the effect remains the same as the creation of these so-called resistant superbugs is further enhanced through a growing industry in antibiotic use on animal agriculture. While this continues to be an expanding field of study, more research gaining significant evidential impact is still needed.
References:
4. Barton, M. (2000). Antibiotic use in animal feed and its impact on human health.
5. Nutrition Research Reviews, 13:279-299.Guidance for Industry. (2017). Food and Drug Administration, 1-18.https://www.fda.gov/downloads/AnimalVeterinary/GuidanceComplianceEnforcement/Gui