99 problems but antimicrobials shouldn't be one of them...part 1

You are faced with a horse, a fever, exam findings suggestive of bacterial infection, and an anxious owner.  Where do you begin? Even when we have already initiated treatment, we have all been in the position where our carefully thought-out plan has not achieved our desired goals.  It is prudent to assess whether our understanding of the disease process at hand is truly complete, if we will choose or have chosen an appropriate therapeutic, and whether we fully appreciate the difficulties our chosen medications may have in meeting our treatment goals.  As we likely use antimicrobials daily in situations where a positive outcome for the animal and client is both needed and expected, a better understanding of the factors governing success of antimicrobials is the first step in ensuring that success.

Consider the most likely organism(s) involved, if any

When first asked to make a decision you won’t have the benefit of bacterial culture or polymerase chain reaction (PCR) results. That is where accurate history, clinical experience, and local knowledge of likely pathogens aid in providing a preliminary identification of the organism(s) likely present.  Relevant history includes any potential exposure of the horse to infectious agents by contact with known or suspected infected horses.  For example, the horse suffering a fever in an environment where strangles has recently been discovered is well-served by considering presumptive treatment for strangles until it can be ruled out. Generally, the presentation of the horse, when matched to previous clinical experience and the findings of a thorough physical examination, will suggest an initial treatment plan likely to be effective against the most probable causes.  Clinical signs present and the site, if any can be localized, of the disease process within the horse also suggest a likely cause.  With high fever, a decision should be made during evaluation whether a viral cause is most likely as this may negate the need for antimicrobial usage. Local knowledge of pathogens most likely present where the affected horse resides, gained through experience treating other horses in the area, improves the likelihood the initially suspected pathogen is responsible.

Optimize your chances of success with an accurate diagnosis

Appropriate sample taking and testing will provide information confirming the chosen treatment path or allow its correction. The first step is using good technique to collect representative samples from the site of infection. Sample handling must be appropriate to avoid degrading pathogens rendering the sample falsely negative. Poor sample handling allows contamination with environmental organisms. Inadequate storage conditions reduce chances of  preservation of the organism before testing is possible. Aging of the sample from any delay in submission further reduces viable organisms decreasing the value of any information obtained.

You can’t always wait for an answer. Another time I will talk about first moves when you’re out there on the spot facing down disease and pestilence.

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