Dermatophyte and Malassezia Ross 2025 with objctives

Superficial Fungal Infections

  • Focus on Malassezia and Dermatophyte

  • Speaker: Sandra Merchant, DVM, Diplomate American College of Veterinary Dermatology

Learner Objectives

  • Recognize dermatophyte species important in dogs and cats:

    • M. canis

    • M. gypseum

    • T. mentagrophytes

  • Identify primary sources for each species.

  • Describe common clinical presentations of dermatophytosis.

  • Know diagnostic techniques for identifying dermatophytosis:

    • Distinguish microscopic appearances of M. canis and M. gypseum macroconidia.

  • List three general principles for treatment of dermatophytosis:

    • Systemic treatment agents for dogs and cats.

    • Instances for topical therapy use.

  • Recognize major underlying factors contributing to Malassezia dermatitis in dogs.

  • Identify common clinical signs of Malassezia in both dogs and cats, and differentiate diagnostic methods.

  • Discuss major systemic and topical therapies for Malassezia dermatitis.

Introduction to Malassezia

  • Characteristics of Malassezia:

    • Lipophilic single-cell yeast.

    • Commonly found in areas like: ear, anal sac, interdigital regions, and mucocutaneous junctions.

    • Functions as a commensal and can act as an opportunistic pathogen (primarily secondary).

  • Clinical Influence:

    • Yeast enzymes alter clinical signs and skin microenvironment.

    • Contributing factors: excessive sebum, moisture accumulation, and disrupted skin barrier.

Factors Affecting Malassezia Proliferation

  • Influences:

    • Allergies, bacterial presence, and inflammation all promote yeast proliferation.

    • Historical use of antibiotics and steroids may impact yeast levels.

    • Some breeds are more susceptible:

      • Basset Hound, Blood Hound, Dachshund, Spaniels, Labrador, Lhasa Apso, Shih Tzu, various terriers, Maltese, Miniature Poodle, German Shepherd.

    • May induce hypersensitivity or enhance allergic reactions.

Malassezia in Cats

  • Rare occurrence unless associated with:

    • Atopic dermatitis, food allergies, ectoparasites, otitis, chin dermatitis.

    • Related serious internal diseases or conditions (e.g., immunosuppressive diseases, thymoma).

  • Most associated breeds:

    • Devon Rex: affects seborrheic areas.

    • Sphinx cats: often presents in claw/claw folds, possible generalization.

Clinical Signs in Dogs

  • Presentations can be focal/multifocal or generalized:

    • Regions affected: periocular, perioral, ventral neck, abdomen, interdigital spaces, claws, posterior legs.

    • Early symptoms: erythema, greasy exudate, scaling, and crusting.

    • Chronic signs: greasy alopecia, lichenification, hyperpigmentation.

    • Notable odor: musty scent.

  • Pruritus:

    • Often pronounced; yeast activates complement leading to inflammation.

    • May be only partially responsive to steroids and certain medications (Apoquel, Cytopoint).

    • Check areas with evidence of seborrhea, hyperhidrosis, or lichenification for yeast.

Clinical Signs in Cats

  • Signs include:

    • Exfoliative erythroderma and greasy/scaling dermatosis.

    • Claw/claw fold dermatitis.

    • Variable pruritus.

  • Evaluate cases with:

    • Prominent scaling/greasy exudate.

    • Significant or recurrent dermatosis.

    • Systemically ill cats exhibiting skin disease symptoms.

Diagnosis of Malassezia

  • Methods of Demonstration:

    • Utilization of cytology, culture, or histopathology.

    • Cytology is the best tool for diagnosis:

      • Use acetate tape or cotton swab for sampling.

      • Identification of yeast significance: 1 or more per oily or flaky field.

  • Culture and biopsy tend to be less reliable:

    • Potentially missed infections in biopsies and no quantitative measures in cultures.

Treatment Considerations

  • Systemic anti-yeast agents include:

    • Ketoconazole, Fluconazole, Itraconazole, Terbinafine.

    • Consider cost and convenience; Itraconazole is typically more expensive.

  • Topical therapies include:

    • Chlorhexidine shampoos, selenium disulfide, miconazole, and various creams/ointments.

Duration of Therapy

  • Duration for treatment is often between 2-4 weeks, may require pulse therapy or continual topical therapy to decrease recurrence.

Dermatophytes Overview

  • Importance in Veterinary Medicine:

    • Infectious, contagious, and zoonotic potential.

  • Major species:

    • Microsporum canis (primary host: cat).

    • Microsporum gypseum (soil-based).

    • Trichophyton mentagrophytes (associated with rodents/farm animals).

  • Infection rates in cats (90% M. canis), dogs (70% M. canis, 20% M. gypseum, 10% T. mentagrophytes).

Clinical Features of Dermatophytes

  • Lesions reflect structures attacked:

    • Classic issues: alopecia, erythema, scaling, crusting varies in severity and distribution.

  • Key indicators:

    • Alopecia often presentation: “If it looks like ringworm, it’s probably Staph!”

    • Papular folliculitis may mimic bacterial infections or demodectic mange.

Zoonosis Considerations

  • Common with Microsporum canis and Trichophyton verrucosum:

    • High-risk populations include young/immunocompromised individuals and professionals working with animals (veterinarians, technicians, shelter workers).

Diagnosis Techniques

  • Evaluate using:

    • Wood's lamp, direct hair examination, trichogram, and fungal culture (Dermatophyte Test Medium - DTM).

  • Wood's Lamp:

    • UV lamp assessment for phosphorescent organisms; identifies M. canis effective glow.

Further Diagnosis Techniques

  • Trichogram:

    • Direct examination of hair samples in mineral oil or KOH for fungal presence.

    • Distinct from macroconidia detection.

  • Fungal Culture:

    • Considered the gold standard for diagnosis despite potential for false positives/negatives.

    • Mackenzie brush technique may yield false positives; hair plucking also effective.

Treatment Overview for Ringworm

  • Clear infection, minimize infectious risks, and decrease environmental contamination.

  • Monitor culture effectiveness throughout treatment.

  • **Topical Options:

    • Lime sulfur and Miconazole/Chlorhexidine formulations are popular choices.**

Systemic Therapy Options

  • Itraconazole best option though costly, effective, and accumulates in skin layers.

  • Terbinafine gaining favor due to side effects.

  • Other systemic agents (Ketoconazole, Fluconazole, Griseofulvin) have varied effects and may not be preferred.

Environmental Decontamination Techniques

  • Steps to minimize risk include:

    • Disinfection and mechanical removal of debris, utilize bleach solutions, and maintain cleanliness with regular vacuuming and washing.