Purdue ushers in pathogen tracking system; FDA wants thresholds for resistance

Washington, D.C.-At presstime, the Food and Drug Administration(FDA) is proposing new animal thresholds for antibiotic approvals, whilea new Purdue University pilot program was just launched to monitor antibioticresistance in companion and food animals.

Officials say these two events will most likely shape the future of antimicrobialuse by veterinarians, and it's not without its share of controversy.

FDA's Center for Veterinary Medicine (CVM) wants to create thresholdsto monitor antibiotic use in food animals, which would signal whether ornot antibiotic resistance is emerging in people. The agency has devisedtwo proposed epidemiological models to accomplish the goal.

The resistance threshold is defined by FDA as the maximum allowable prevalenceof resistant bacteria isolated from animal-derived food. The human healththreshold sets limits on unacceptable prevalence of infections in humanstreated with the antibiotic of concern, "or for which the resistanceis attributable to the use of an antimicrobial drug in animals."

If accepted, FDA would implement post-approval surveillance on new productsapproved by the agency, and if antimicrobials are believed to be causingresistance in people, the agency could pull products from the market.

The FDA discussion document says, "For example, if changes are observed,but the resistance threshold has not been reached, voluntary mitigationstrategies by groups such as the pharmaceutical industry, food animal productiongroups and the veterinary community (e.g. education, labeling changes, userestrictions, etc.) may be implemented to curtail further loss of susceptibility.However, if surveillance data indicate that the resistance threshold hasbeen exceeded, CVM would initiate procedures to withdraw from the labelany animal species that has reached or exceeded its threshold."

All this has the American Veterinary Medical Association (AVMA) veryconcerned.

In fact, the most recent FDA proposals are already being met with resistancefrom industry groups. Officials believe it could stifle development of novelantibiotic therapies by pharmaceutical manufacturers for animal health,even though the risk to human health has not yet been scientifically proven.

But AVMA is not stopping there.

Last month, the novel antimicrobial susceptibility testing program, coordinatedat Purdue University and sponsored by the AVMA and American Associationof Veterinary Laboratory Diagnosticians, was just unveiled to the profession,reports Dr. Lyle Vogel, director of scientific activities for AVMA.

Monitoring resistance

Vogel adds the most recent launch of an entirely new antimicrobial trackingprogram is the right step forward to keep the currently approved antibioticsfor animal health viable. In addition, new antimicrobial use guidelineswere recently approved by the AVMA Executive Board for bovine and poultry.

Vogel explains that AVMA's lastest antimicrobial susceptibility pilotprogram-headed by Dr. Ching Ching Wu, professor of veterinary pathobiology,of the Animal Disease Diagnostic Laboratory at Purdue's School of VeterinaryMedicine - will be launched this month.

The pathogen surveillance program is just one part of a larger AVMA strategyto help address issues about antimicrobial resistance and potential implicationsfor veterinarians and their patients, Vogel says.

The new tracking system will provide veterinarians critical surveillanceinformation initially funded for five species: bovine canine, equine, porcineand poultry.

The goal, officials say, is to provide an early warning to veterinarianson animal pathogens, which could ultimately save the efficacy of certainkey antibiotics over time.

The Purdue-led surveillance program will incorporate samples from a networkof 15 reporting laboratories.

New guidelines

In addition, AVMA's Executive Board recently approved guidelines on prudentantimicrobial use for cattle and poultry.

The bovine guidelines were drafted by the American Association of BovinePractitioners (AABP).

The guidelines say, "The AABP recognizes that proper and timelymanagement practices can reduce the incidence of disease and therefore reducethe need for antimicrobials; however, antimicrobials remain a necessarytool to manage infectious disease in beef and dairy herds.

The guidelines add, "The veterinarian's primary responsibility tothe client is to help design management, immunization, housing and nutritionalprograms that will reduce the incidence of disease and the need for antimicrobials."

The guidelines go on to offer more than 17 suggestions on the selectionand use of antimicrobials, and also address proper on-farm use.

Guideline advice from AABP says, "The veterinarian should have strongclinical evidence of the identity of the pathogen causing the disease, basedupon clinical signs, history, necropsy examination, laboratory data andpast experience."

Also, antimicrobial selection should be appropriate for the target organismand should be administered at a dosage and route that are likely to achieveeffective levels in the target organ.

The guidelines add, "Antimicrobials should be used with specificclinical outcome(s) in mind, such as fever reduction, return of mastiticmilk to normal, or to reduce shedding, contagion and recurrence of disease."

The poultry guidelines, which are much more comprehensive, were draftedby the American Association of Avian Pathologists with input from the NationalChicken Council and National Turkey Federation.