Direct Skin Scraping With Digestion

This technique is used to recover small ectoparasites, particularly the various species of tiny mites associated with mange.

Deep scraping of the skin surface with a scalpel blade held perpendicular to the surface will recover sufficient epidermal tissue, skin debris and hair to be able to detect mange mites, if present, both those that burrow in the skin (e.g. Sarcoptes) and those that live on the skin surface (e.g. Psoroptes). To maximize parasite recovery, the scraping must be deep enough to draw blood (but not to bleed out the animal!). Usually the scalpel blade used is dipped into a little mineral oil before being used for the scraping. This helps the material collected, including the mites, adhere to the blade.  Mite recovery is enhanced if the scraping collected is digested in warm 5% potassium hydroxide and the digest subjected to a sugar flotation for mite recovery prior to microscopic examination. This digestion technique is also of value when examining large amounts of material.

 Clippers

• Scalpel blade
• 5% KOH
• Wide test tube
• Boiling water bath
• Centrifuge
• Sugar flotation solution
• Wooden applicator stick
• Slides and coverslips
• Microscope

1. Select an area for scraping at the edge of a visible lesion, where mites are likely more plentiful.
2. Clip hair from area selected for scraping.
3. Squeeze the skin between thumb and forefinger and holding the scalpel blade perpendicular to the surface of the skin scrape the skin with enough pressure for blood to start to ooze from the skin surface.
4. Take skin scraping samples from skin lesions in multiple locations on the animal.
5. To one volume of scrapings add 10 volumes of 5% KOH in a wide test tube.
6. Place test tube in a boiling water bath until epidermal scales, hair and the exudate dissolves (approximately 5 minutes).
7. Centrifuge the tube for 3 minutes at 1500 rpm.
8. Decant the supernatant and re-suspend the sediment with the sugar flotation solution.
9. Mix well with a wooden applicator stick then carefully top up the tube with sugar flotation solution until there is a slightly convex meniscus.
10. Very carefully vertically place a coverslip on top of the meniscus ensuring that there is minimal dripping of solution down the outside of the tube.
11. Centrifuge at approximately 1500 rpm for 3 minutes – mites rise and debris sinks.
12. Very carefully remove the coverslip by lifting vertically and place on a microscope slide (Note: if >50% of the space beneath the coverslip in the tube is occupied by air bubbles, start again).
13. Examine the preparation at 40x total magnification for the presence of mites.

In some types of mange (e.g. Sarcoptes), it may be very difficult to find mites in scrapings, and several areas of the skin may have to be examined. For all types of mange, it is important to scrape from lesions that appear “active” – reddened, weeping fluid, covered with new scab material.  When examining digested scrapings, it is very important to look very carefully. Sometimes only fragments of mites or mite eggs are present; often these are sufficient for identification. It is also important to realize that, on occasion, free-living arthropods may be present on the skin surface, particularly of carcasses; these have to be differentiated from parasites.