ANTIBIOTICS IN FOOD ANIMALS: THE CONVERGENCE OF ANIMAL AND PUBLIC HEALTH, SCIENCE, POLICY, POLITICS AND THE LAW

BY NANCY E HALPERN, DVM

MAY 3, 2009

ABSTRACT

The use of antibiotics in food animals, to prevent and/or control disease in these animals, has been a subject of discussion between the medical and veterinary and animal agricultural sectors and related national and international government entities for decades, because of concerns about the resulting increase in antibiotic resistance such practices facilitate. The underlying premise is that use of antibiotics in food animals leads to resistance of the bacteria consumed by humans, and reducing the effectiveness of antibiotics used to treat the resultant disease, usually diarrhea since it had created the resistant bug to which the human was exposed.

There are many significant variables to consider when analyzing the emergence of antibiotic resistance. First, an understanding of the science of microbiology is required, including the types of bacteria that exist, some harmful and some considered beneficial. The discovery and subsequent development and use of antibiotics, including the scope and limitations of such use must be considered. Then the evolution of bacterial resistance must be understood-how it develops, how it is spread, what parameters exist in the bacterial environment to promote or inhibit the development, mechanisms and success of resistance, and what measures can be employed to minimize or eliminate these actions.

Classes or types of antibiotics have been developed to kill or prevent the growth of specific types of bacteria. Both pathogenic, or disease-causing bacteria, as well as non-pathogenic, or commensal, bacteria exist in the digestive tracts of animals, sometimes causing disease. Exposure to antibiotics has resulted in antibiotic resistance from the selection of inherent or acquired mechanisms of resistance. Naturally occurring antibiotics and antibiotic resistance predates human evolution, but as pharmacologically produced antibiotic use expanded, so did evolutionary selection of bacteria resistant to antibiotics. Whether inherently or genetically acquired, bacterial resistance can spread horizontally to other bacteria within the same environment, or vertically, upon bacterial reproduction. Although understanding the specific mechanisms of resistance is beyond the scope of this discussion, the fact that resistance has been identified amongst non-pathogenic and pathogenic bacteria that commonly inhabitants animals’ intestinal tracts, to all known antibiotics. Since the discovery of antibiotics, this subsequent resistance has been a known sequellae to its use, but concerns about antibiotic resistance are growing, as the availability of newer antibiotics is diminishing.

The scope of antibiotic use in human and animal populations and horticultural applications has only begun to be quantified worldwide. Federal regulations vary amongst countries regarding the approval and authority to provide or prescribe different types and quantities of antibiotics in different settings, and as importantly, systems for the collection of data regarding antibiotic use and surveillance for bacterial species, including identification of resistant organisms is severely lacking in many countries, and lacks uniformity and completeness when information is collected. There is widespread agreement that information not yet available is fundamental to our understanding of potential risk and harm. Despite the lack of definitive evidence proving antibiotic use in animals causes harm to humans, some countries, and many public health proponents in the United States, have been sufficiently convinced that antibiotics used for humans should not be allowed for use in food animals, in subtherapeutic and or even for therapeutic purposes.

In the United States, the FDA has recently withdrawn prior approval for Enrofloxacin therapeutic treatment for infectious disease in poultry, stating that the Food and Drug Cosmetic Act prohibits consideration of benefits when determining if antibiotics in animal treatment are safe for humans, including any identified in risk analyses typically employed by scientists and often federal agencies. At issue was the effect of the use of enrofloxacin in poultry, a fluoroquinilone antibiotic also relied upon in human medicine to treat diarrhea commonly caused by Campylobacter bacteria, would have on human health. The FDA Commissioner withdrew approval for the use of enrofloxacin in poultry, using case law to bolster his reasoning.

The tension between the animal health and pharmacologic scientific community and the laws governing use of antibiotics in animals, especially food animals, is exemplified in this FDA decision.

While disagreements persist between many animal and public health advocates on the issue of harm to humans resulting from antibiotic use in food animals, most parties and agencies I acknowledge the importance of risk assessment tools to determine the safety of this use for animals and humans. When including all relevant parameters using a robust risk assessment tool, it is apparent that the abolishment of antibiotic use in animals, beginning with food animals, creates more potential hazards than have been proven to exist from their continued use.

A prohibition on the use of antibiotics in food animals has proven detrimental to both animals and humans in other countries. The benefits of antibiotics used judiciously in animals reduces bacterial contamination of food, minimizes subsequent human exposure, enhances the safety of food and decreases manure production. Antibiotics that minimize disease and mortality in animal populations allow producers in the U.S. to continue to survive providing the country and 35% of the rest of the world, safe wholesome food. Should antibiotics be prohibited in these populations, bacterial infections, animal disease and mortality will increase, and the welfare of these animals will suffer. Many in the farming community will be unable to withstand the increased economic burdens resulting from increased disease and animal loss, increased resources needed to feed fewer animals for longer periods of time, and the increased scrutiny from animal rights organizations accusing them of animal cruelty. This will not result in less protein eaten in the U.S., but more animal protein imported from other countries where safety and welfare requirements fall short of national standards, leading to diminished human health.