Contributors: Rosanna Marsella, Catherine Fraser
Species: Canine | Classification: Techniques
- Essential diagnostic test in almost all cases of skin disease.
- Demodex spp Skin: demodectic mange.
- Sarcoptes spp Skin: sarcoptic mange.
- Cheyletiella spp Skin: cheyletiellosis.
- Trombicula spp Skin: neotrombicula autumnalis infestation.
- Otodectes cynotis Ear: parasitic otitis.
- Notoedres Notoedres cati (head mange) (rarely reported in dogs).
- Cheap, effective diagnostic aid.
- Part of minimal work-up for all cases of canine skin disease.
- Adaptation of technique for specific parasite enhances success of diagnosis.
- Skin biopsy Biopsy: skin to rule out demodecosis may be necessary in the Shar Pei, severe cases of pododermatosis and in cases where excessive fibrosis is present, eg lick granuloma.
- Hair pluck Trichography (hair plucking): ectoparasites rarely found except in demodecosis.
- Few min to collect sample, <10 min to examine sample.
Criteria for choosing test
- Essential for all dogs with skin disease.
- Sample examination.
- Clippers to clip hair.
- Liquid paraffin.
- Mineral oil.
- Scalpel blade //www.vetlexicon.com10 or 15.
- Glass microscope slides.
- Margin of pinnae if scabies is suspected.
- Comedones if demodecosis is suspected.
- New lesions.
- Non-excoriated skin.
- Owner or nurse holding.
Step 1 -
- Clear site: clip hair if necessary with clippers.
Step 2 -
- Prepare lesion: moisten with mineral oil.
Step 1 - Scrape skinIf suspect demodecosis, 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 or Sarcoptes ensure capillary bleeding is produced (not blood from laceration), for deep scrapings.
- If Sarcoptes is suspected, choose new lesions at predilection sites, elbow stifles and ear pinna. Large areas should be scraped.
Step 2 - Prepare smear
- Smear material evenly onto glass microscope slide.
- Add additional liquid paraffin if necessary.
- Place coverslip over material.
- 10-15 skin scrapings should be performed if Sarcoptes infestation is suspected.
Step 1 - Examine smear
- Examine under low magnification and phase contrast.
- 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.
In some cases of scabies, feces may be the only finding.
Step 2 - Mites visible on microscopy
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.
- Very few mites present, eg scabies.
- Recent references from PubMed and VetMedResource.
- Vos J H, van den Ingh T S, van Mil F N (1989) Non-exfoliative canine cytology - the value of fine needle aspiration and scraping cytology. Vet Q 11 (4), 222-231 PubMed.
- Smith E K (1988) How to detect common skin mites through skin scrapings. Vet Med 83 (2), 165-170 VetMedResource.
Other sources of information
- Moriello K A & Mason I S (eds) (1995) Handbook of Small Animal Dermatology. 1st edn. Pergamon. pp 31-33. (Step by step procedure.)
- Muller G H et al (1995) Muller and Kirk's Small Animal Dermatology. 5th edn. Philadelphia: W B Saunders. pp 94-98. (Detailed account with particular reference to techniques of scraping for different mites.)