|Sample Requirement||Turnaround Time|
Skin scraping/hair (sterile pot)
Microscopy (same working day)
With culture (bacterial - 2-3 working days; fungal - 7-21 working days)
Skin scraping and hair pluck samples are collected from horses and ponies for the confirmation of suspected dermatophyte infections or ectoparasite infestations. Samples should be collected from fresh skin lesions (edges of the lesions if extensive) using a fresh sterile scalpel blade. The plucked hairs and the scraped skin layers, down to haemorrhage, should be collected into a sterile universal container.
The hairs and scraped skin layers should be incubated for 15 minutes in warm 40% potassium hydroxide (KoH) and then examined for clear ringworm spores in broken hair shafts and free whole or fragmented ectoparasitic mites, including Sarcoptes, Psoroptes, Chorioptes and Demodex species.
If negative for dermatophyte spores after KoH incubation, skin scrapings can be incubated overnight in blue/black ink and then examined for blue/black stained spores in clear broken hairs.
Skin scraping samples should be incubated for bacterial and fungal growth. The latter (taking up to 3 weeks) will differentiate the different ringworm-causing dermatophytes, including Trichophyton and Microsporum spp.
Microscopic and fungal culture results for dermatophytes do not always correlate. Positive microscopic findings but negative culture results may suggest that the spores were not viable at the time of scraping. Negative microscopic findings but positive culture results may suggest that too few spores were present in the sample to be detected in spite of careful examination.
If Dermatophilus congolensis (‘rain scald’) infection is suspected on clinical grounds, moist lesions should be collected and submitted for impression smear stained with methylene blue to look for characteristic chains (‘railroad track’), sometimes in branched conformation.