Uncertainties and Concerns: Animal Drugs and Microbial Resistance
Hunter, Beatrice Trum., Consumers' Research Magazine
In 1965, a large outbreak of severe salmonellosis in England caused widespread illness and some deaths. The outbreak was traced to a multiresistant strain of the pathogen. Researchers connected the disease in humans to the use of antibiotics in farm animals. The pattern of antibiotic resistance in the affected humans was similar to the pattern of antibiotic resistance in affected calves.
An official commission investigated the outbreak. In 1969, the commission issued its "Report of Joint Committee on the Use of Antibiotics in Animal Husbandry and Veterinary Medicine," known popularly as the Swann Report. It was the first official document to question the wisdom of using with animals antimicrobial drugs that also were used with humans.
Following the Swann Report, in 1970 the United Kingdom passed legislation strictly limiting antibiotic use. The Netherlands, all Scandinavian countries, Germany, and Canada followed. The United States considered a ban, but it was never approved.
Now, more than three decades later, the concerns are still present and have increased because of many instances of antibiotic resistance. Yet scientific understanding of the problem is incomplete, and uncertainties still exist.
The practice of using antimicrobial drugs with food animals began in the 1940s. The drugs have been used at high levels to cure or contain animal diseases. However, it was discovered that the same drugs, if used routinely at low levels, could promote animal growth. This feature still is not well understood. Systematic, low-level use enhances feed efficiency and fights infections usually not detected without clinical examination. These features translate into greater profitability in livestock management.
Unfortunately, the antimicrobial drugs used with food animals are either the same as or related to drugs used with humans, too. The low-level use with animals, especially to promote growth, has been of special concern. The practice threatens human health because drug residues can remain in the final food products and cause human illness.
The Food and Drug Administration has established specific time periods between the last administration of the drugs and the slaughter of the animals, to limit drug residues from remaining and being consumed by humans. These rules/are based on knowledge of the time needed for the breakdown of active ingredients in the drugs. Despite these regulations, the FDA conducts frequent recalls of animal-based foods because of illegal residues still present. This problem continues to pose an immediate threat to human health. However, there is another concern regarding the use of these drugs with food animals that poses an even greater long-range threat: resistance.
Scientists have found that the cautions expressed in the Swann Report were warranted. Indeed, some pathogens (especially bacteria) have become resistant to antimicrobial drugs. This finding raises concerns about the role of animal drug use in the emergence of drug-resistant bacteria in humans and the ability of health care professionals to cope with the threat to human health. Some microorganisms are naturally resistant to some antimicrobial drugs. Others become resistant, by mutation, by incorporating genetic material for resistance from other microorganisms, by ingestion, or by cellular contact.
Despite the passage of many years, scientists admit that considerable uncertainty exists about many aspects of microbial resistance. Data are limited about the public health threat. The U.S. General Accounting Office (GAO) found that differences of opinion exist among various branches of the federal government about the risk to public health posed by antimicrobial drug use in food animals, and no unanimity concerning the best plan of action. The GAO recommends that various involved branches of government work together to address the critical information gaps, and then develop science-based decisions. …