September 30, 2002

Volume 74, Number 40 Feedstuffs

REPRINT

THE WEEKLY NEWSPAPER FOR AGRIBUSINESS

Human health risk from animal antibiotic use small

SAN DIEGO, CAL. A group of human microbiologists, risk assessors, veterinarians and animal health experts has concluded that while a theoretical hazard to human health arises from the use of antibiotics in food animals, an examination of the facts shows that the actual risk is extremely small, according to a statement from the Animal Health Institute.

The independent expert group evaluated available data on the effects of antibiotics in humans and animals and attempted to confirm or deny a link between antibiotic resistance in animals transferring to humans. They met Sept. 26 in San Diego, a day prior to the opening of the 42nd Interscience Conference on Antimicrobial Agents & Chemotherapy. In 50 years of antibiotic use in animals and man, the development of resistance in animals has not made a major impact on human and animal health, and such a development seems unlikely to happen overnight now, said Dr. Ian Phillips, emeritus professor of medical microbiology at the medical school of Guy's and St. Thomas Hospitals, University of London.

Phillips, who is chairing the group of experts, said evaluating available facts convinced the group that whereas the use of antibiotics in humans and animals undoubtedly leads to resistance and while some resistant organisms reach man via the food chain, little additional harm results from resistance even when infection occurs.

Much of the debate over the issue of antibiotic resistance has centered on the use of antibiotics in animals to promote growth.

The case against antibiotic growth promoters has relied very heavily on antibiotic-resistant enterococci, a group of bacterial organisms that cause no disease in animals but can cause disease in man and might be zoonotic (transmittable from animals to man under natural conditions). However, new surveillance data show that enterococci resistance is increasing in areas where antibiotic growth promoters have been withdrawn. Vancomycin-resistant enterococci (VRE) and Synercid-resistant E. faecium are becoming more prevalent as a cause of infections in humans in Europe at a time when these resistant organisms are becoming less prevalent in animals and food products following the antibiotic growth promoter ban, said group member Dr. Ronald N. Jones, referring to two commonly used antibiotics that are effective against various bacteria, including en-terococci.

Jones is principal investigator of the SENTRY Antimicrobial Resistance Surveillance program, a global network of healthcare facilities monitoring resistance levels in human bacteria, providing the world's largest database of antibiotic resistance. SENTRY Program data from parts of the world where Synercid was used for patients show an increasing prevalence of resistance in the absence of the genetic mechanisms of resistance commonly found in most animal strains, Jones said. We thus conclude that the increasing prevalence of resistance was not due to passive acquisition of resistant strains of animal origin but due to antibiotic use in humans, he said.

A major topic of the group discussion was the possible adverse effects of antibiotic bans on animal health and wellbeing.

This issue has been studied extensively in Denmark, where the use of antibiotic growth promoters was phased out beginning in 1997 through 1999. Danish farmers have found that banning antibiotic growth promoters has caused pigs to get more cases of diarrhea, especially baby pigs, said group member Dr. John Waddell, a Nebraska veterinarian who has toured several Danish pig farms. The pigs have slower post-weaning growth rates and increased production costs. Waddell added that Danish pigs, because of their increased prevalence of diarrhea and other diseases, require more therapeutic antimicrobials, according to DANMAP, the Danish national database that tracks patterns of antibiotic usage and resistance from human and veterinary medicine and food hygiene.

While only 48,000 kg of antibiotics were used in Denmark for treatment of food animals in 1996, that amount increased to about 57,000 kg in 1997, to 57,300 kg in 1998, to 61,900 kg in 1999, to 80,600 kg in 2000 and to 91,602 kg in 2001. At the same time, human cases of salmonella and campylobacter have reached record levels in Denmark, and the proportion of multiple antibiotic-resistant salmonella DT104 has doubled since 1997, Waddell said.

The group of experts concluded that banning any antibiotic usage in animals, in the absence of a full risk assessment, is not useful and could even be harmful to both human and animal health. Rather than banning the use of antibiotics in animals, we believe efforts should focus on reducing the transmission of all foodborne pathogens regardless of their antibiotic susceptibility, said Phillips. This can only occur through insistence on good hygienic practices on farms, in abattoirs, during distribution and marketing of food and in the proper handling and cooking of food and must be accompanied by consumer vigilance. Considerable progress has been made in the U.S. as demonstrated by the decline over the past five years of foodborne illness reported by the Centers for Disease Control & Prevention, Phillips concluded.