Diagnostic Laboratory Section

EXAMINATION OF SKIN SCRAPING

Collection & processing

• Remove hair coat by gentle clipping (the hair can be mounted and examined separately).
• The surface of the skin can then be scraped using a blunt scalpel blade.
• The scrapings so collected have to be transferred to a boiling tube, and heated with 10% potassium hydroxide (KOH).
• The fluid is then centrifuged at 1000 rpm for 5 minutes to concentrate mites, which can be collected from the sediment.
• Discard the supernatent, collect a drop of the sediment, transfer to a slide and examine for mites.

Processing on slide if material is scanty

• The emulsion of scanty material (superficial epidermis) is spread over a microscope slide.
• 2 or 3 drops of 10% KOH is added to it and mixed.
• It is then warmed for about 3 minutes.
• Covered with a glass coverslip and examined under the microscope.
• This technique can be used to identify surface mites and multiple scrapings should be taken to increase the likelihood of ectoparasites detection.

Deep skin scraping (deep epidermal examination)

• The skin scraping procedure is repeated until capillary blood oozes out. This technique is useful in the diagnosis of burrowing and deep follicular mites such as Sarcoptes scabiei and Demodex spp. Multiple sites should be scraped to maximize detection of ectoparasites.

Commom ectoparasites

Demodex sp		Elongated body(cigar shape), short stumpy legs, transversly striated abdomen
Sarcoptes sp		Body is globose and striate with scaly and spinose areas, posterior pairs of legs short, not extending beyond body margin, pedicels bear sucker or bristle and not segmented, terminal anal opening.
Psoroptes sp		Oval in shape, all legs extend beyond body margin, long segmented pedicels with suckers on end of some legs. Anus is terminal. Dorsal surface devoid of scales and spines.