October 5, 2010
It is time for some straight talk about the risks of using massive amounts of antibiotics in livestock and poultry. I don’t know one infectious disease expert who would disagree that there are direct links between antibiotic use in food animals and antibiotic resistance in people. Period. If you don’t believe me just ask Rear Admiral Ali Kahn, Assistant Surgeon General and Acting Deputy Director for the CDC’s National Center for Emerging and Zoonotic Infectious Disease. Just this summer, during a hearing before the House Energy and Commerce Committee, Dr. Kahn testified that, “there is unequivocal evidence and relationship between [the] use of antibiotics in animals and [the] transmission of antibiotic-resistant bacteria causing adverse effects in humans.”
Knowing this, I continue to be frustrated with the fact that Agriculture Secretary Tom Vilsack does not publically recognize that the industrial food animal production system is a leading contributor to the increase of antibiotic resistance in pathogens that infect people and animals. Earlier this month at a National Cattlemen’s Beef Association meeting, Vilsack reportedly responded to a question about the Preservation of Antibiotics for Medical Treatment Act (PAMTA) by saying the, “USDA’s public position is, and always has been, that antibiotics need to be used judiciously, and we believe they already are.”
That quote had me scratching my head when I read it in a New York Times Op-Ed a couple of weeks ago. The Times’ editors interpreted the statement as saying Vilsack believes there is no need to change antibiotic use policy among food animal producers. That contradicts the positions of both the FDA and CDC. The Times pointed out that while neither regulatory agency is doing enough to address the problem both, at least, recognize that current antibiotic use should change.
Congresswoman Louise Slaughter (D-NY) and Senator Dianne Feinstein (D-CA), the primary sponsors of PAMTA, which calls for limits on the non-therapeutic use of certain antibiotics in livestock production, were perplexed with Secretary Vilsack’s comment too. They recently requested that Vilsack clarify his stance on the issue. In a letter, Slaughter and Feinstein wrote, “Media reports suggest that you may have mischaracterized our legislation and made statements that run contrary to previous positions taken by Department officials. We hope that you can provide us with reassurance that your off-the-cuff remarks were taken out of context, and that you remain committed to protecting human and animal health”
I called the Secretary’s office for a clarification myself. A USDA spokesperson sent me the following statement:
“USDA believes that antibiotic use should be used judiciously to slow the development of resistance in animals. USDA believes livestock producers are good stewards, use antibiotics judiciously, but there are some bad actors, and continued use can develop resistance. USDA wants to be a partner with Congress, producers and other federal partners to address this important issue.”
This statement does little to address the issue at hand. The problem does not lie with a few rogue producers. Rather, there is an industry standard of feeding livestock and poultry low concentrations of antibiotics and other antimicrobials, like arsenicals, in their feed to promote growth. (All of which is approved by the FDA, by the way.) Considering industry produces more than 10 billion food animals a year (the majority chicken and hogs) the amount of antibiotics used in food animals is astronomical. Case in point, researchers at Johns Hopkins Bloomberg School of Public Health estimate that the amount of antibiotics North Carolina hog producers use in their swine feed every year exceeds the total amount of antibiotics used to treat infections in people nationwide. It is estimated that as much as 70 percent of the antimicrobial drugs used in the US are administered to animals not to treat disease, but to purportedly promote growth or prevent the spread of pathogens among livestock and poultry living in intensive confinement.
All uses of antibiotics contribute to drug resistance. While human medicine plays a large role in the antibiotic drug resistance problem, new research is clearly showing that resistant bugs from food animals are starting to show up in people more and more. Johns Hopkins Bloomberg School of Public Health and Hershey Medical Center researchers recently published a study that confirms other research indicating that hospitals are no longer the main source of exposure for methicillin resistant Staphylococcus aureus or MRSA. And researchers in Europe have published evidence that livestock production is increasingly becoming a major source for the Super Staph bug.
The reason why PAMTA is focusing on the non-therapeutic use of antibiotics in animals is that it is contrary to everything we have known for 70 years about preserving these drugs. The amounts of antibiotics used in animal feeds are low and are not intended to kill bacteria. That creates a problem first recognized by the inventor of penicillin, Alexander Fleming, who warned in 1945 that, “the greatest possibility of evil in self-medication is the use of too small doses so that instead of clearing up infection, the microbes are educated to resist penicillin.” Many infectious disease experts believe that we may very well be close to a post-antibiotic era, which could mean a return to a time when a simple bacterial infection could cause your child, your parents or you serious health problems or even death.
In their letter to Secretary Vilsack, Senator Feinstein and Congresswoman Slaughter tried to clear up what they call common misperceptions about their legislation:
“The Preservation of Antibiotics for Medical Treatment Act does not ban the use of antibiotics. And in fact we share your belief banning all uses of antibiotics would be counterproductive. Instead, the Preservation of Antibiotics for Medical Treatment Act addresses usage of seven antibiotics that are critical in human medicine, phasing them out for non-therapeutic uses in livestock production.”
I respectfully suggest that the common misconception about PAMTA Senator Feinstein and Congresswoman Slaughter should focus on is the misguided belief by many people that their bill would ban the use of antibiotics to treat sick food animals. The legislation allows veterinarians to authorize proper use of antibiotics to treat or prevent disease. .
While I support the proposed legislation to limit antibiotic use in food animals, I have continually made it clear that the current language in PAMTA should be stronger. I believe the concession to only focus on the so-called “seven antibiotics that are critical in human medicine” weakens the bill. If we are going to be up front with the public, we must make it clear that bacteria don’t differentiate between types of antibiotics, whether they are approved for human medicine or not.
Dr. Ellen Silbergeld, professor of environmental health sciences at the Johns Hopkins Bloomberg School of Public Health, recently testified before Pennsylvania’s state legislature regarding its own proposed legislation to limit antibiotic use in food animals. She warned that, “bacteria respond to chemical structures, not brand names, and resistance to one member of a pharmaceutical class results in cross resistance to all other members of the same class.” For example, she noted that resistance in campylobacter (a nasty bug that the USDA says is the second most frequently reported cause for foodborne illness) to the antibiotic enrofloxicin (an antibiotic approved for pets and other domestic animals, commonly called Baytril) results in resistance to the very important human therapeutic antibiotic ciprofloxacin. Both antibiotics are two of more than 30 variations of the fluroquinolone class of antibiotics. As Silbergeld explains when bacteria develop resistance to one member of that class of antibiotics it can be resistant to all.
Authors made certain that language in PAMTA would ensure that any, “derivative of a drug that is used in humans or intended for use in humans to treat or prevent disease or infection caused by microorganisms,” would be banned from being used as a growth promoter in food animals. But – and this is a big “but” – the bill does not address the fact that the use of any antibiotic can lead to a pool of resistance that can affect every antibiotic class – important to both human and animal medicine.
Silbergeld has long warned that antibiotic resistant bacteria can share the genes (bits of DNA) that code for resistance with other bacteria in the environment and therefore readily transfer antibiotic resistance. Sharing genes between bacteria is almost as easy for these organisms as forwarding an email to a friend; only bacteria are exchanging genetic code information. Resistance genes for multiple classes of antibiotics can be shared in the same “email,” or what scientists call plasmid “cassettes.” For instance, some isolates of Salmonella and Campylobacter have been found to have taken up a “cassette” of resistance genes that protect them from as many as 17 different antibiotic drugs.
What this means is that not only can bacteria share resistance genes within the same class of antibiotics such as the fluoroquinolines class antibiotics containing enrofloxicin (restricted for veterinary use) and ciprofloxacin (critical to human medicine), but also bacteria have the capability of exchanging resistance genes between different classes of antibiotics like we’ve seen in Salmonella and Campylobacter. Allowing the non-therapeutic use of any antibiotic in food animals, regardless of whether it is defined as important to human medicine or not, could still lead to the development of bacteria that are resistant to an antibiotic that you and I may one day depend on.
The concept behind PAMTA is an important one. We must stop wasting one of medicine’s most important lifesaving discoveries simply as a way to increase the growth of food animals and subsequently profit for the food industry. If PAMTA is not passed this year I hope that the next version would follow more closely the recommendations from the Pew Commission on Industrial Farm Animal Production’s final report, which calls for “the phasing out and then banning the non-therapeutic use of [ALL] antimicrobials in food animal production.”