Contributors: Rosanna Marsella, Ian Mason, David Scarff, Catherine Fraser
Species: Feline | Classification: Techniques
- Essential diagnostic test in almost all cases of skin disease.
- Demodex spp Demodectic mange.
- Cheyletiella spp Cheyletiellosis.
- Trombicula spp Neotrombicula autumnalis infestation.
- Otodectes cynotis Otodectes disease.
- Notoedres spp Notoedres cati (head mange).
- Sarcoptes spp Sarcoptic mange.
- Lynxacarus radovskyi Lynxacarus radovskyi.
- Cheap, effective diagnostic aid.
- Negative findings do not rule out the presence of mites.
- Numerous scrapings often required.
- Adaptation of technique for specific parasite may enhance success of diagnosis.
- Tape strips (may detect Cheyletiella spp).
- Coat brushings (may detect Cheyletiella spp).
- Skin biopsy Biopsy: skin - unreliable.
- Hair pluck Trichography (hair plucking): ectoparasites rarely found except in demodicosis Demodectic mange or cheyletiellosis Cheyletiellosis (eggs glued to hairs) and Lynxacarus (eggs glued to hairs).
- Few minutes to collect sample, <20 minutes to examine sample.
Criteria for choosing test
- Essential for all cats with skin disease.
- Sample examination.
- Scissors to clip hair.
- Binocular microscope with x4 & x10 objective lens.
- Liquid paraffin or potassium hydroxide (KOH).
- Scalpel blade (no.10 or 15).
- Glass microscope slides.
- Cover slips.
- New lesions.
- Non-excoriated skin.
- Scaling skin.
- Owner or nurse holding.
Step 1 -
- Clear site: if necessary clip hair with scissors.
Step 2 -
- Prepare lesion: moisten with liquid paraffin.
- If using KOH do not apply to skin.
Step 1 - ScrapingIf suspect demodicosis: squeeze skin between thumb and forefinger to extrude mites from hair follicles.
- Hold scalpel blade between thumb and second finger using first finger to guard against laceration perpendicular to skin.
- Firmly scrape skin in direction of hair growth.
If suspect Demodex spp Demodex cati and Demodex spp or Sarcoptes spp Sarcoptic mange, ensure capillary bleeding is produced (not blood from laceration) for deep scrapings.
Step 2 - Slide preparation
- Smear material evenly onto glass microscope slide.
- Add additional liquid paraffin if necessary or KOH.
- Place coverslip over material.
Step 3 - Repeat scrape
- At least 2 or 3 scrapings per case for screening purposes. Several scrapings may be necessary if mite infestation strongly suspected.
Step 1 - Microscopic examination
- Examine under low magnification.
- Start at one end of collected material and move microscope stage across in a horizontal or vertical direction.
- At edge of slide move over one field of vision and go back in opposite direction.
- Continue back and forth until all scraped material on slide has been examined.
Look for movement of mites if using liquid paraffin.
Reasons for Treatment Failure
- Inadequate number of scrapes taken.
- Scrape not deep enough (if Demodex spp).
- Insufficient time spent examining collected material, eg Sarcoptes mites can be difficult to find.
- Recent references from PubMed and VetMedResource.
- Hazelrigg D E (1978) Scraping for scabies. Am Fam Physician 17 (1), 129 PubMed.
Other sources of information
- Moriello K A and Mason I S (1995) Handbook of Small Animal Dermatology. Eds K A Moriello and I S Mason. 1st edition. Pergamon. pp 31-33. (Step by step procedure.)
- Muller G H et al (1995) Muller and Kirk's Small Animal Dermatology. 5th edition. Philadelphia: W B Saunders. pp 94-98. (Detailed account with particular reference to techniques of scraping for different mites.)