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
- Spores residing in soil
- Spores in other outdoor or indoor environments
Individuals at increased risk of infection include1
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
Dermatophytosis can be focal or generalized1,3 affecting
- +/- 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
- 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
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
- 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.
- Mattei AS, Beber MA, Madrid IM. Dermatophytosis in small animals. SOJ Microbiol Infect Dis. 2014;2(3):1-6.
- Weese S. Ringworm for vets. Centre for Public Health & Zoonoses; University of Guelph, Ontario, Canada; January 2009; http://www.wormsandgermsblog.com. Accessed February 2016.
- 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.
- Moriello K. Feline dermatophytosis–aspects pertinent to disease management in single and multiple cat situations. J Feline Med Surg. 2014;16(5):419-431.
- 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.
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
- Courtesy of MedVet's Dermatology Department, Cincinnati, Ohio
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