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APRUMA: Antimicrobials and Disease Diagnosis

When a disease occurs, the veterinarian examines the animal(s) and the circumstances in which they are kept


Disease diagnosis and treatment are closely linked.

When a disease occurs, the veterinarian examines the animal(s) and the circumstances in which they are kept. On the basis of this information s/he will diagnose the disease and decide on an intervention This could be management advice on the way that the animals are kept (feeding/housing) or the prescription of a suitable (antimicrobial) therapy If necessary, a sample may be sent to a laboratory for analysis to establish the exact bacterium causing the disease and its sensitivity and so choose the most appropriate treatment However, if laboratory confirmation is not possible, the choice of antimicrobials is then a matter of experience and of clinical judgement based on the previous bacterial sensitivity on the farm in question The veterinarian will evaluate the result of his/her treatment of choice and, if necessary, adjust this.

Frequently, animals are kept in groups and whilst this is beneficial from practical husbandry and animal welfare aspects, it means that the group may be at risk when a disease strikes As a result, it is sometimes necessary to treat the group This would be the case where it is known that an infectious disease is present and where experience shows that the disease will infect most, or even all of the animals in the group once one animal show symptoms of infection Such use is sometimes termed ‘metaphylaxis’.

Bacterial infections in large flocks or herds often appear at identifiable and predictable stages during the life time of the animal, e g respiratory problems after regrouping, colibacillosis during the post-weaning period, shipping fever following transport, etc Treating in situations like this is referred to as prophylactic treatment The farmer and the veterinarian are familiar with imminent disease hazards on their farms, and early action, carefully and selectively carried out, is a necessary part of disease management.

As may be appreciated, preventative action is similar to that practiced in human medicine in cases such as bacteria meningitis outbreaks in schools or colleges where the group of students potentially exposed will be treated in a preventative manner.

Having taken a decision to treat with an antimicrobial, the first consideration for a veterinarian is to select the most appropriate one The next step is to use a specific authorised medicinal product based on the diagnosis made for the disease condition involved and on the expertise of the veterinarian. A range of antimicrobials are available and the veterinarian must use his/her professional knowledge in the context of a specific disease situation to choose the product with the most appropriate spectrum. (A range of antimicrobial products should be used over time to guard against the possible emergence of resistance.)

The continuous use of the same product for the same type of indication (e.g. respiratory, intestinal, systemic, et c.) over a long period of time should be viewed with caution, unless preliminary testing in the laboratory has shown satisfactory susceptibility of the  bacteria involved. The veterinarian may use a range of products over time to guard against the possible emergence of resistance, sometimes known as a ‘rotation programme’ in order to safeguard long-term effectiveness and to minimise resistance selection pressure.

Antimicrobials are critical when treating, preventing and controlling animal diseases. In managing animal diseases, veterinarians often focus on controlling the disease on a herd or flock basis. In human medicine, treatment with antimicrobials is almost always directed at the individual. Prophylactic or metaphylactic administration of antimicrobials is a practice that has shown to be beneficial to maintaining herd or flock health, like in mastitis disease management. Availability of a variety of antimicrobials is a critical concern to food-animal veterinarians.

It is necessary to have a wide range of safe and effective products from all antimicrobial classes available to the veterinarian in treating animal diseases in order to discourage the potential selection of resistance by the overuse of a restricted number of products.

The farmer, the veterinarian and other experts must work together to ensure that the outcome of treatment is effective. The farmer may be required to administer subsequent treatments. Where this is the case, it is essential that all instructions are followed. The farmer should report any unexpected delay in recovery to the veterinarian. If necessary, an alternative form of treatment may be commenced if the animal is not responding as expected.


Veterinarian to make final choice

Today, a broad range of antimicrobials is available in the marketplace. They vary in many different ways such as route of administration, speed and extent at which they are taken up by the animal, modes of action, speed and extent of penetration into the tissues, etc.

At the same time, micro-organisms vary in the way they are affected by the different antimicrobials. For this reason, the selection of an antimicrobial must always be based on several criteria, such as the micro-organism affecting the animal(s), the occurrence of resistance against antimicrobials, the animal species, the way the antimicrobial has to be administered, etc. The selection of the proper treatment must always be made by the veterinarian after examining the animals, the local situation and making a diagnosis.



In exceptional cases, where no medicine is authorised, there is a possibility for the veterinarian to use, for example, products that are authorized in other countries or for humans or other animal species. This exception exists to avoid unacceptable suffering of animals. In these cases the veterinarian has to follow specific steps, the so-called cascade, and s/he has to make sure that there is no risk for the animal(s) concerned and for consumers of food products of animal origin.