Skin: Wood's lamp test in Dogs (Canis) | Vetlexicon
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Skin: Wood’s lamp test

ISSN 2398-2942

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Introduction

  • The tryptophan metabolites of certain dermatophytes, eg Microsporum canis Microsporum canis fluoresce under ultra-violet light of 330-365 nm wavelength Ringworm Woods lamp.
  • A Wood's lamp is a source of ultra-violet light filtered through a cobalt or nickel filter.
  • Microsporum canis is the only dermatophyte species of importance in veterinary medicine which fluoresces.

Uses

  • Screening for Microsporum canis Microsporum canis infection.
  • Selection of appropriate hairs for culture.
  • Not effective to monitor infection.
    Positive Wood's lamp examination is only suggestive, not diagnostic, of Microsporum canis infection.
    Negative Wood's lamp examination does not rule out Microsporum canis infection as up to 50% of strains of M. canis do not fluoresce.

Advantages

  • Rapid screening technique.

Disadvantages

  • Not all strains of Microsporum canis fluoresce - 30-50% show positive fluorescence.
  • Medication, eg iodine, destroys fluorescence.
  • Only actively infected growing hairs fluoresce.

Technical problems

  • Lamp must be turned on for 5-10 min before use to ensure that the temperature-dependent wavelength is stable.
  • Lamp must be held over the skin lesions for at least 5 min because infected hairs may need to be exposed to the lamp for several minutes before they start to fluoresce. Positive hairs will glow an apple-green color.
  • Over-interpret results because scale, medication and certain bacteria, eg Pseudomonas aeruginosa Pseudomonas aeruginosa and Corynebacterium minutissimum, may have a greenish hue.
    Fluorescence must be seen in the individual hair shafts, not scale.

Time required

Preparation

  • 5-10 min for Wood's lamp to warm up.

Procedure

  • > 5 min.

Decision taking

Criteria for choosing test

  • Any localized or multifocal alopecia as a primary problem.

Requirements

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Preparation

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Technique

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Aftercare

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Sparkes A H, Stokes C R, Gruffydd-Jones T J (1995) Experimental Microsporum canis infection in cats - correlation between immunological and clinical observations. J Med Vet Mycol 33 (3), 177-184 PubMed.
  • Sparkes A H, Gruffydd-Jones T J, Shaw S E et al (1993) Epidemiological and diagnostic features of canine and feline dermatophytosis in the United Kingdom from 1956 to 1991. Vet Rec 133 (3), 57-61 PubMed.
  • Caplan R M (1967) Medical uses of Wood's lamp. JAMA 202 (11), 1035-1038 PubMed.