Lapis ISSN 2398-2969

Skin: Wood's lamp test

Contributor(s): Stephen White, Vetstream Ltd, Beatrice Funiciello

Introduction

  • The tryptophan metabolites of certain dermatophytes, eg Microsporum canis, M. equinum, M. audouinii, M. distortum and Trichphyton schoenleinii, fluoresce under ultraviolet light of 253.7 nm wavelength.
  • A Wood's lamp is a source of ultra-violet light filtered through a cobalt or nickel filter.
  • Rabbits are most commonly affected by Trichophyton mentagrophytes and Microsporum canis. Other dermatohytic fungi cultured from rabbits include T. verrucosum, T. ajelloi, T. terrestre, T. schoenleinii, M. nanum, M. gypseum, M. persicolor, M. cookei and M. distortum. Wood’s lamp examination will therefore detect only some cases of dermatophytosis in rabbits.
  • Microsporum canis is the only dermatophyte species of importance in veterinary medicine which fluoresces.

Uses

  • Screening for Microsporum canis Microsporum canis, M. equinum, M. audouinii, M. distortum and Trichphyton schoenleinii infection Ringworm.
  • Selection of appropriate hairs for culture.

Positive Wood's lamp examination is only suggestive, not diagnostic of Microsporum canis infection.

Negative Wood's lamp examination does not rule out infection.

Advantages

  • Rapid screening technique for dermatophyte infections that produce fluorescence.

Disadvantages

  • Fungal culture or the presence of arthrospores on direct microscopic examination of hairs is essential for diagnosis, so Wood's lamp examination is a complementary aid.
  • Fungal culture is needed to determine the species of the organism and is a more sensitive method of diagnosing dermatophytosis than hair examinations.
  • Not all (but most) cases of M. canis infection fluoresce.
  • Some topical products, soap residue and seborrheic material may fluoresce, but lack the apple green/emerald green of M. canis.
  • Only actively infected growing hairs fluoresce.
  • If hairs are positive on Wood's lamp examination, these hairs should be submitted for fungal culture and/or observed under the microscope for fungal arthrospores.

Requirements

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Preparation

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Procedure

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Moriello K A, Coyner K, Paterson S & Mignon B (2017) Diagnosis and treatment of dermatophytosis in dogs and cats. Clinical Consensus Guidelines of the World Association for Veterinary Dermatology. Vet Derm 28 (3), 266-268 PubMed.
  • Kraemer A, Mueller R S, Werckenthin C, Straubinger R K & Hein J (2012) Dermatophytes in pet guinea pigs and rabbits. Vet Microbiol 157 (1-2), 208-213 PubMed.
  • Harvey C (1995) Rabbit and Rodent Skin diseases. Semin Avian Exotic Pet Med 4 (4), 195-204 SciDirect.

Other sources of information

  • Meredith A (2014) Dermatoses. In: BSAVA Manual of Rabbit Medicine. Eds: Meredith A & Lord B. BSAVA, UK. pp 255-263.
  • Miller W H, Griffin C E & Campbell K L (2013) Diagnostic Methods. In: Muller and Kirk’s Small Animal Dermatology. 7th edn. Elsevier, USA. pp 57-107.
  • Miller W H, Griffin C E & Campbell K L (2013) Dermatoses of Exotic Small Mammals. In: Muller and Kirk’s Small Animal Dermatology. 7th edn. Elsevier, USA. pp 844-887.
  • Sant R & Rowland M (2009) Skin Disease in Rabbits. In Pract 31 (5), 233-238.


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