Contributors: Rosanna Marsella, Catherine Fraser

 Species: Canine   |   Classification: Techniques

Introduction Requirements Preparation Procedure Aftercare Outcomes Further Reading

Introduction

  • Essential diagnostic test in almost all cases of skin disease.

Uses

Parasite identification

Advantages

  • Cheap, effective diagnostic aid.
  • Part of minimal work-up for all cases of canine skin disease.

Disadvantages

Technical Problems

  • Adaptation of technique for specific parasite enhances success of diagnosis.

Alternative Techniques

  • 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.

Procedure

  • Few min to collect sample, <10 min to examine sample.

Decision Taking

Criteria for choosing test

  • Essential for all dogs with skin disease.

Requirements

Personnel

Nursing expertise

  • Sample examination.

Materials Required

Minimum equipment

  • Clippers to clip hair.
  • Microscope.

Minimum consumables

  • Liquid paraffin.
  • Mineral oil.
  • Scalpel blade //www.vetlexicon.com10 or 15.
  • Glass microscope slides.
  • Coverslips.

Preparation

Site Preparation

  • Margin of pinnae if scabies is suspected.
  • Comedones if demodecosis is suspected.
  • New lesions.
  • Non-excoriated skin.

Restraint

  • Owner or nurse holding.

Procedure

Approach

Step 1 -

  • Clear site: clip hair if necessary with clippers.

Step 2 -

  • Prepare lesion: moisten with mineral oil.

Core Procedure

Step 1 - Scrape skin

If 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.

Exit

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

Aftercare

Outcomes

Complications

  • None.

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.

Further Reading

Publications

Refereed papers

  • 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.)