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Relationship between types of pathogenic microorganism isolated from Thoroughbred racehorses with infectious dermatitis and course of treatment

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Ibaraki University College of Agriculture Graduate School of Agriculture
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We isolated and identified 261 aerobic bacterial strains and 121 fungal strains from the lesions of 140 Thoroughbred racehorses with infectious dermatitis. Drug susceptibility testing was performed for the bacteria isolated. Each specimen was then classified into three categories based on the type of microorganism isolated: i) Group C, coagulase-positive staphylococci (CPS); ii) Group F, pathogenic fungi; and iii) Group N, other resident microorganisms not classified in other groups. Skin rash morphology and the course of treatment were examined for correlations with group classification. The results showed no relationship between skin rash morphology and group classification. As for the course of treatment, most cases required topical application of antibiotics selected based on drug sensitivity testing of the affected area to achieve resolution of symptoms. These included multiple cases from Group F in which pathogenic fungi such as Trichophyton spp. were isolated. Infectious dermatitis in racehorses is currently treated simply by differentiating between bacterial and fungal infections through experience-based visual inspection and palpation alone, and by providing pharmacotherapies such as antibiotics or antifungal agents. However, the present findings suggest that treatment based upon practitioner experience and skin rash morphology alone may be ineffective. Regardless of the morphology, the affected area should be thoroughly cleansed first with an antiseptic that is effective against both bacteria and fungi. If improvement is still not seen, medications should be introduced based on microbial identification and drug susceptibility testing.