Equis ISSN 2398-2977

Dermatophytosis

Synonym(s): Dermatomycosis, Ringworm

Contributor(s): Vetstream Ltd, Sue Paterson, Dawn Logas, Rosanna Marsella, Beatrice Funiciello

Introduction

  • Superficial skin infection due to dermatophyte fungi.
  • One of the commonest and most important skin diseases of horses.
  • One of the most commonly mis-diagnosed skin diseases in horses.
  • An important zoonosis.
  • Prevalence of infection is high in racehorses.
  • Cause: Trichophyton equinum Trichophyton spp, Microsporum canis, M. gypseum, T. mentagrophytes (Arthroderma vanbreuseghemi) and M. equinum are commonly involved.
  • Signs: scaling, crusting and hair loss.
  • Diagnosis: signs; confirmed by examination of hair pluckings or biopsy and culture.
  • Treatment: self-limiting, topical and/or systemic treatment may be used to limit time course and severity of disease Therapeutics: skin.
  • Prognosis: spontaneous remission unless concurrent immunodeficiency, or re-infection occurs.
Print off the Owner factsheet on Ringworm - a fungal infection to give to your client.

Pathogenesis

Etiology

  • Most commonly involved: Trichophyton equinum Trichophyton spp (T. equinum var. equinum and T. equinum var autotrophicum).
  • Trichophyton mentagrophytes Trichophyton spp (Arthroderma vanbreuseghemii).
  • Microsporum equinum.
  • M. canis.
  • T. verrucosum.
  • M. gypseum.
  • Rare or extremely rare isolates include:
    • Keratinomyces ajelloi.
    • M. nanum.
    • M. audouinii.
    • M. cookei.
    • M. distortum.
    • T. tonsurans.
    • T. rubrum.
    • T. granulosum.
    • T. terrestre.
    • T. schoenleinii.
    • Epidermophyton floccosum.

Predisposing factors

General

  • Poor hygiene.

Specific

  • Skin damage due to tack rubbing or ectoparasites.
  • Overcrowded, warm damp stables.
  • Exposure to asymptomatic horses that can function as carriers.
  • Immunocompromised horses and horses treated with glucocorticoids are most prone to the disease.

Pathophysiology

  • Presence of dermatophyte fungi and disruption of the stratum corneum → infection of keratin-bearing tissues.
  • Infection of anagen hair follicle → proliferation of the hyphae on the hair surface, penetration towards the hair bulb, production of keratolytic enzymes (keratinases), invasion of the hair shaft.
  • Hair breakage, inflammatory folliculitis → papules, pustules, patchy alopecia.
  • Reaction to fungal toxins → erythema, pruritus, crusting and scaling.
  • Can transfer to in-contact humans Trichophyton: lesion 01 - human (ringworm) Trichophyton: lesion 02 - human (ringworm).
  • Allergen hypersensitivity of the fungi → more severe reaction → erythema, pruritus, edema, suppuration and necrosis.
  • Colonization of dermis and subcuts by the fungi following rupture of the follicle may occur → dermatophytic pseudomycetoma.
  • Humoral response is usually present, however, does not play a major role in protective immunity while T cell immunity is crucial in the development of immunity and resolution of the infection.
  • As hairs enter the telogen phase most cases resolve (keratin production stops → fungal growth stops).
  • There may be some differences of pathogenicity of various dermatophyte strains and the host's response is crucial in determining the clinical lesions.

Timecourse

  • Incubation 4-30 days.
  • Lesions may continue to spread across the body depending on hair stage and individual immunity, spontaneous remission usually occurs in 1-4 months in immunocompetent subjects.

Epidemiology

  • Transmission is by direct or indirect contact - grooming equipment, tack, clippers or contaminated box.
  • In contact horses may be affected, but also individuals of other species (dogs, cats, humans).

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Chollet A et al (2015) An outbreak of Arthroderma vanbreuseghemii dermatophytosis at a veterinary school associated with an infected horse. Mycoses 58 (4), 233-238 PubMed.
  • Weese J S & Yu A A (2013) Infectious folliculitis and dermatophytosis. Vet Clin North Am Equine 29 (3), 559-575 PubMed.
  • Galuppi R, Gambarara A, Bonoli C, Ostanello F & Tampieri MP (2010) Antimycotic effectiveness against dermatophytes: comparison of two in vitro tests. Vet Res Commun 34 (Suppl 1), S57-61 PubMed.
  • Chung T H et al  (2009) A rapid molecular method for diagnosing epidemic dermatophytosis in a racehorse facility. Equine Vet J 42 (1), 73-78 PubMed.
  • Nardoni S, Franceschi A & Mancianti F (2007) Identification of Microsporum canis from dermatophytic pseudomycetoma in paraffin-embedded veterinary specimens using a common PCR protocol. Mycoses 50 (3), 215-217 PubMed.
  • Pilsworth R C & Knottenbelt D (2007) Dermatophytosis (ringworm). Equine Vet Educ 19 (3), 151-154 WileyOnline.
  • Apprich V, Spergser J, Rosengarten R & Stanek C (2006) In vitro degradation of equine keratin by dermatophytes and other keratinophilic fungi. Vet Microbiol 114 (3-4), 352-358 PubMed.
  • Cook C P, Scott D W, Erb H N & Miller W H Jr (2005) Bacteria and fungi on the surface and within noninflamed hair follicles of skin biopsy specimens from horses with healthy skin or inflammatory dermatoses. Vet Derm 16 (1), 47-51 PubMed.
  • Rochette F, Engelen M & Vanden Bossche H (2003) Antifungal agents of use in animal health – practical applications. J Vet Pharmacol Therap 26 (1), 31-53 PubMed.
  • Vanden Bossche H, Engelen M & Rochette F (2003) Antifungal agents of use in animal health – chemical, biochemical and pharmacological aspects. J Vet Pharmacol Therap 26 (1), 5-29 PubMed.
  • Latimer F G, Colitz C M, Campbell N B & Papich M G (2001) Pharmacokinetics of fluconazole following intravenous and oral administration and body fluid concentrations of fluconazole following repeated oral dosing in horses. Am J Vet Res 62 (10), 1606-1611 PubMed.
  • Viani F C, Dos Santos J I, Paula C R, Larson C E & Gambale W (2001) Production of extracellular enzymes by Microsporum canis and their role in its virulence. Med Mycol 39 (5), 463-468 PubMed.
  • Muhsin T M, Aubaid A H & Al-Duboon A H (1997) Extracellular enzyme activities of dermatophytes and yeast isolates on solid media. Mycoses 40 (11-12), 465-469 PubMed.
  • Paterson S (1997) Dermatophytosis in 25 horses - a protocol of treatment using topical therapy. Equine Vet Educ 9 (4),171-173 VetMedResource.
  • Schutte J G & van den Ingh T S (1997) Microphthalmia, brachygnathia superior, and palatocheiloschisis in a foal associated with griseofulvin administration to the mare during early pregnancy. Vet Q 19 (2), 58-60 PubMed.
  • Scott D W (1994) Marked acantholysis associated with dermatophytosis due to Trichophyton equinum in two horses. Vet Dermatol 5 (3), 105 VetMedResource.
  • Pascoe R R (1984) Infectious skin diseases of horses. Vet Clin North Am Large Anim Derm, 27-46 PubMed.

Other sources of information

  • Scott D W & Miller W H Jr (2011) Diagnostic Methods. In: Equine Dermatology. 2nd edn. Saunders, St. Louis. pp 35-100.
  • Scott D W & Miller  W H Jr (2011) Fungal Skin diseases. In: Equine Dermatology. 2nd edn. Saunders, St. Louis. pp 171-211.
  • Knottenbelt D C (2009) Fungal diseases. In: Pascoe’s Principles and Practice of Equine Dermatology. 2nd edn. Ed: Knottenbelt D C. Saunders, St. Louis. pp 167-185.


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