June 2017
Dermatology
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Dermatophytosis is a pathogenic, keratin-digesting, fungal infection of the hair, outermost layer of the skin (stratum corneum), and claw.1-5 Although uncommon, infection can also occur in the deep layer of the skin and subcutaneous tissue.1 In dogs and cats, dermatophytosis is most often caused by Microsporum canis, M gypseum, or Trichophyton mentagrophytes.1-5 

All three organisms are zoonotic,1-5 with transmission most often linked to M canis (which also is zoophilic, as elaborated later). Of note, because M gypseum inhabits soil, it is zoonotic and geophilic1,4; whereas T mentagrophytes is found on rodents or in their environment, making this organism also zoophilic.1,4 

Dermatophytosis is acquired following contact with

  • Infected hair or scale from animals
  • Fomites
  • Spores residing in soil 
  • Spores in other outdoor or indoor environments

Individuals at increased risk of infection include1

  • Young
  • Geriatric 
  • Immunocompromised 

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In Persian cats and Yorkshire terriers, genetics also may be involved, as both breeds commonly have repeat infections or difficulty clearing infections.1,2 

The preference of M canis for an animal host makes this organism a zoophilic dermatophyte1,4; it also is the most frequent cause of dermatophyte infection in small animals and can be carried by asymptomatic cats.1,5M canis infection is particularly important to avoid in catteries, shelters, and multipet environments or households.2,4,6 

Clinical Presentation

Dermatophytosis can be focal or generalized1,3 affecting

  • Face
  • Ears 
  • Legs 
  • Tail
  • +/- trunk 

Most patients have little to no evidence of pruritus, although chronic and extensive cases can be severely pruritic. 

On skin, clinical presentation most often involves1-5

  • Partial to complete alopecia
  • Scale/dry or greasy seborrhea
  • Erythema
  • Papules
  • Pustules
  • Crusts
  • Epidermal collarettes (ringlike appearance)
  • +/- feline miliary dermatitis (crusted papules)

Nodules, draining tracts, feline chin acne, paronychia (inflammation of the claw fold), onychomycosis (fungal infection of the claw), or onychodystrophy (abnormal growth of the claw) occur less commonly.1-5

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Global Relevance 

Dermatophytosis occurs worldwide; however, prevalence of specific organisms varies by region.3,4 Because dermatophytosis is not a reportable disease, the overall incidence remains unknown.3 Dermatophytes grow best in warm, humid environments, including tropical and subtropical geographic areas.4 Risk for disease transmission increases with crowding, close contact, skin trauma, or contact with chronic moisture.3

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References and author information Show
References
  1. Pendergraft J. Clinical knowledge insights: fungal & yeast dermatoses: dermatophytosis. Excellence in Dermatology: Diagnostic Techniques & Clinical Insights. Parsippany, NJ: Zoetis; 2013 (follow-up yearly updating); https://www.zoetisus.com/Conditions/Pages/Dermatology/dermatophytosis. Accessed April-May 2016. 
  2. Mattei AS, Beber MA, Madrid IM. Dermatophytosis in small animals. SOJ Microbiol Infect Dis. 2014;2(3):1-6.
  3. Weese S. Ringworm for vets. Centre for Public Health & Zoonoses; University of Guelph, Ontario, Canada; January 2009; http://www.wormsandgermsblog.com. Accessed February 2016.
  4. Center for Food Security and Public Health. Dermatophytosis. Ames, IA: Iowa State University; May 2005 (updated March 2013; http://www.cfsph.iastate.edu/Factsheets/pdfs/dermatophytosis.pdf. Accessed April-May 2016. 
  5. Moriello K. Feline dermatophytosis–aspects pertinent to disease management in single and multiple cat situations. J Feline Med Surg. 2014;16(5):419-431. 

 

Suggested Reading

  • Moriello K, et al. Diagnosis and treatment of dermatophytosis in dogs and cats. Vet Dermatol. 2017; 28: 266-303.
  • Skin dermatologists. Tinea (fungal) infection: tinea capitis head); ectothrix, endothrix; http://www.skindermatologists.com/tinea-capitis.html. Accessed April-May 2016.

 

Photo Courtesy

Questions 1, 2, 4, 9

  • Reused with permission: Dr. David Ellis, Mycology Online, School of Biological Sciences, The University of Adelaide, Australia; published/revised 2016-2017

Questions 3, 5, 6

  • Reused with permission: Dr. Ramόn M. Almela, AniCura Kleintierspezialisten Augsburg, Germany; July-August 2016

Questions 7, 8, 10

Author

Ashley E. Detwiler

DVM, DACVD MedVet, Cincinnati, Ohio

Ashley E. Detwiler, DVM, DACVD, is a board-certified veterinary dermatologist involved with all aspects of small animal dermatology at MedVet, a comprehensive emergency and specialty facility where she practices in Cincinnati and Dayton, Ohio. Although Dr. Detwiler handles all aspects of dermatology, her special interests focus on otitis, resistant skin infections, environmental and dietary allergies, and immune-mediated/autoimmune disease. She has been awarded multiple grants to research dermatology issues, including multidrug and methicillin-resistant staphylococcus infections. Dr. Detwiler earned her veterinary degree from Mississippi State University, followed by completing a 2-year residency in small animal dermatology at Michigan State University.

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