What’s the big deal about animal antibiotic usage?

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Therapeutic vs. non-therapeutic antibiotic usage in food animals has recently come under debate in Washington D.C., and repeatedly in California. Mike Apley, a veterinary clinical pharmacologist at Kansas State University, offers the following comments on therapeutic and non-therapeutic animal antibiotic usage:

“Therapeutic antibiotic use definitely includes the case where we have an animal displaying clinical signs of a disease and we intervene with a drug.  Our best chance for therapeutic success is to address the infection as early as possible in the disease process.  This is the basis for the label claims for prevention and control of disease outbreaks.

“In the case of non-therapeutic antibiotic use, if we take this as lacking any components of the therapeutic definition, then it would be the use of a drug in the absence of clinical disease.  We now get into the discussion of whether addressing disease in the incubation stage is an appropriate use of antimicrobials; this discussion almost always includes the consideration of the mixed incubating and non-incubating status of animals in a population where antimicrobials may be applied to the population as a whole. The question now becomes clinical vs. subclinical disease, especially when we know there is a high probability of disease occurrence.

“The definition of non-therapeutic use contained in H.R. 1549, currently in the U.S. House of Representatives is “…any use of the drug as a feed or water additive for an animal in the absence of any clinical sign of disease in the animal for growth promotion, feed efficiency, weight gain, routine disease prevention, or other routine purpose.”

“Another thing lost on the vast majority of the human population is that the issues surrounding each drug/pathogen combination are different. This legislation reflects the unsophisticated approach of legislative bodies to scientific issues. I was shocked in the California hearing to hear methicillin-resistant staph aureus (MRSA) and E. coli O175:H7 presented as diseases in humans due to antibiotic use in animals. If you work in an animal production unit where MRSA is present in the animals, research shows you may be colonized by that strain of MRSA. However, the strains of MRSA associated with community disease outbreaks in humans are predominantly different from the strains encountered in animals. E. coli O157:H7 is a disease that the cattle industry takes very seriously and is working very hard to address (a new vaccine has just been released).   However, the inability to use antibiotics to treat O157:H7 is not due to antibiotic resistance, it is due to the antibiotics actually increasing toxin release by the bacteria. Another major piece of misinformation presented in the California hearing was the Union of Concerned Scientists (UCS) claim that 70 percent of the antibiotics produced in the United States are used for nontherapeutic purposes in food animals. This highly flawed “study” even includes drugs that aren’t marketed in the United States in the estimates.   

“Vancomycin is an important drug for the treatment of resistant Gram (+) infections in humans.   It is a glycopeptide; this group is banned from use in food animals in the United States and has never had a label for such use. Vancomycin-resistant enterococci (VRE) are a big problem in human therapeutics, and an example of where a human resistance problem can’t be pinned on animal agriculture. 

“Synercid® is a streptogramin that is also very important for resistant Gram (+) infections in humans. A close relative in the same streptogramin group, Virginiamycin, is approved for feed use in cattle, poultry and swine.  A recent risk assessment by the Food and Drug Administration Center for Veterinary Medicine was unable to show any link between this use in animals and Synercid® resistance in humans.

“Do the food animal industries need to carefully evaluate the impact of our antimicrobial use on food borne Salmonella pathogens?  You bet, but when people start throwing around resistance problems like MRSA, foodborne pathogens like E. coli O157:H7, or the UCS report numbers in the resistance discussion, it is a clear sign they are looking for anything they can bend to advance their agenda.

“Also, the media continually mixes route of administration with purpose. There are clear therapeutic antibiotic uses which may be delivered through the feed.

“Use for strictly growth promotion is confusing because the increases in gain and or feed efficiency may come from subclinical disease suppression or prevention. The logical progression of this argument is then how much of the necessity of prevention or control is due to the nature of the production systems. That is the crux of the issue. Another confusing concept is that while the percentage of pathogen isolates that are "resistant" may increase during antibiotic use in the feed, the overall load of the pathogen in the animal may decrease.

“So, the debate now moves to the issue of what happened in Denmark. My interpretation of the numbers is that total antibiotic use went down with the feed ban, but the amount used for disease treatment rose sharply. There is also debate on exactly what happened to human resistance levels. A peer-reviewed report on what happened in Denmark will be published soon in the Journal of the American Veterinary Medical Association.

“I do not for a minute propose that antibiotic use in animal agriculture occurs in a vacuum. As an industry, we are responsible for the safety of our product and the people that consume it. I just ask that, in this internet-driven, junk-science age, our legislative representatives take a minute to insist their staffers find actual credible evidence to factor into their decisions.   

“A bookend to these comments comes from Carl Sagan: ‘We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology.’”

 



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