The purpose of this work was to set a benchmark for a monitoring and surveillance programme on the volumes of the eighteen classes of antimicrobials available and consumed by animals for the benefit of animal health in South Africa. In setting up such a programme, risk assessment and possible management and communication strategies of the potential health risks emanating from antimicrobial resistance in bacteria from animals and man were considered and the survey was compared with other overseas surveillance programmes established in Sweden, Denmark, the United Kingdom and Australia. The aim of the study was to contribute to the establishment of future surveillance programmes that will provide direction for the prudent and rational use of antimicrobials, involving all the relevant stake-holders, in order to preserve the future efficacy of those antimicrobials that are currently available. Such programmes will harmonize with international initiatives and contribute to the provision of databases for policy recommendations in South Africa. There are several benefits to the implementation of such surveys and addressing topical and relevant issues of antimicrobial use in the domain of animal health and its possible impact on human health. Furthermore, policy decisions to address concerns regarding antimicrobial resistance may be reached in a more informed and judicious manner, with the aim that the efficacy of available antimicrobials may be preserved for use in future generations of humans and animals. The authorized antimicrobials available in South Africa were firstly reviewed and compared with the volumes of antimicrobials supplied by the veterinary pharmaceutical companies. The majority of antimicrobials were registered under the Stock Remedies Act 36 of 1947. It was found that the class of antimicrobial representing the most registered products was the tetracyclines, followed by the penicillins, the sulphonamides, macrolides, lincosamides and pleuromutilins. This correlated well with the volumes of antimicrobials supplied, as these classes of antimicrobials also represented the top four groups of antimicrobials consumed. Eight of the pool of twenty-five veterinary pharmaceutical companies approached provided more detailed information on the volumes of antimicrobials consumed for the years under review, namely 2002 to 2004. The potency of antimicrobials was also requested, in order to establish trends of increasing or decreasing potency of the active ingredients, versus the volumes of antimicrobials supplied. It was established within the scope of this study, that the majority of consumed antimicrobials was from the classes of macrolides, lincosamides, and pleuromutilins, followed by the tetracycline class, the sulphonamide group and fourthly the penicillins. The potency of the active ingredients supplied by the companies did not change and therefore had no impact on the interpretation of antimicrobials consumed. These results give cause for concern in terms of the possibility of cross-resistance between antimicrobials used in the domain of animal health, and those used in the human medical field. There is also another concern, namely the exposure of humans to veterinary drug residues in food, causing modifications in the bacterial ecology of the human gut, thereby leading to a possible perturbation in the protective human gut barrier with overgrowth and invasion of pathogenic bacteria. Although much has been written about the possibility of anaphylactic reactions occurring in sensitized human individuals from â-lactams and macrolides administered in food animals, this issue has been reviewed extensively and it has been concluded that allergies from antimicrobial residues in the diet are extremely rare. The macrolide tylosin was the most extensively sold antimicrobial of all. Tylosin is one of four antimicrobials that was banned by the EU in 1999 because of its structural relatedness to therapeutic antimicrobials used for the treatment of disease in human medicine. The other three classes mentioned above, the penicillins, tetracyclines and sulphonamides are also relevant because of well-documented evidence of the ability to select for resistance or because of their structural relatedness to human therapeutic antimicrobials and their use in humans. The value of sales of antimicrobials were provided by SAAHA (South Africa Animal Health Association) and also scrutinized within the context of this study in order to obtain meaningful data on the national consumption of antimicrobials. However, as discussed in Chapter 5, the data were not of any value within the context of this study because the sales data were provided in monitory terms only. Volumes of sales of feed were also obtained and companies that mix feed approached to ascertain the percentages of antimicrobial medicated feeds consumed. It was ascertained in this survey that 68,5% of the grand total of antimicrobials surveyed during 2002 to 2004, were administered as in-feed medications. Tylosin was the most extensively used in-feed antimicrobial, followed by oxytetracycline, zinc bacitracin and olaquindox. This result emphasizes the importance of establishing a monitoring programme for the volumes of antimicrobials used, as many growth promoters used in-feed are administered at sub-therapeutic levels over long periods of time that tend to select for antimicrobial resistance. Whereas 17,5% of the total volume of antimicrobials utilized were parenteral antimicrobials, antimicrobials for water medication constituted 12% of the total. “Other” dosage forms such as the topical, aural, ophthalmic, and aerosol antimicrobials and intra-uterine pessaries and tablets constituted 1,5% of the total. Intramammary antimicrobials represented 0,04% of the total. In Chapters 1, 5&6 the surveillance systems for veterinary antimicrobials used by other countries are discussed and compared. It was concluded that a combination of the surveillance systems applied by Australia and the United Kingdom is the best model (with modifications) to apply to the animal health situation in South Africa. Such a surveillance system of the volumes of veterinary antimicrobials consumed should ideally be implemented in conjunction with a veterinary antimicrobial resistance surveillance and monitoring programme to generate meaningful data that will contribute to the rational use of antimicrobials in order to preserve the efficacy of the existing antimicrobials in South Africa. Possible trends of antimicrobial usage in animals may be uncovered over time from implementing a programme for the volumes of antimicrobials used and thereby lead to proactive application of rational policies for the veterinary use of antimicrobials. This information can also be compared with international data, in order to harmonize as much as possible with global monitoring programmes of veterinary antimicrobial usage. Copyright
Dissertation (MMedVet)--University of Pretoria, 2010.