Ringworm (Dermatophytosis: Microsporum and Trichophyton spp.)
Introduction
Ringworm, also known as dermatophytosis, is a highly contagious fungal skin disease affecting a wide range of domestic and wild animals, as well as humans. It is caused by keratinophilic fungi of the genera Microsporum and Trichophyton. The disease is characterized by superficial infection of keratinized tissues such as hair, skin, and claws.
Etiology
Causative Fungi
- Microsporum canis (cats, dogs – very common zoonotic species)
- Microsporum gypseum (soil-associated dermatophyte)
- Trichophyton mentagrophytes (rodents, rabbits, livestock)
- Trichophyton verrucosum (cattle – important in bovine dermatophytosis)
Organism Characteristics
- Keratinophilic fungi (feed on keratin)
- Grow in hair shafts, skin, and nails/claws
- Produce arthroconidia (infective spores)
- Survive long periods in the environment
Epidemiology
Species Affected
- Cattle (especially calves – T. verrucosum)
- Dogs and cats (M. canis)
- Horses
- Rabbits and rodents
- Humans (zoonotic transmission)
Transmission
- Direct contact between infected animals
- Indirect transmission via contaminated fomites (bedding, grooming tools, housing)
- Environmental contamination with spores
Risk Factors
- Young age (immature immune system)
- Overcrowding and poor hygiene
- Stress (transport, weaning)
- High humidity and warm conditions
- Skin trauma or ectoparasites
Pathogenesis
Infection of Keratinized Tissues
Fungal spores adhere to hair shafts or skin and germinate, invading keratinized tissues.
Keratin Degradation
- Fungi produce keratinases that digest keratin
- Leads to hair shaft weakening and breakage
Inflammatory Response
- Host immune response causes erythema, scaling, and crust formation
- Severity depends on host immunity and species
Self-Limiting Nature
- Many infections are self-limiting in immunocompetent animals
- Chronic infections occur in immunosuppressed or young animals
Clinical Signs
Skin Lesions
- Circular, alopecic lesions (“ring-like” appearance)
- Scaling and crusting
- Erythema (redness)
- Broken hairs
Distribution
- Face, ears, neck, and limbs (common in small animals)
- Head and neck (common in cattle)
Species-Specific Features
- Cattle: thick crusts and circular lesions on head and neck
- Cats: variable lesions; may be asymptomatic carriers
- Dogs: patchy alopecia and scaling
- Rabbits: mild to severe crusting dermatitis
Summary for Practitioners
Ringworm should be suspected in young animals with circular alopecic skin lesions, especially in crowded housing conditions.
Postmortem Findings
Gross Lesions
- Superficial skin lesions with crusting
- Hair loss in affected areas
- No systemic lesions in uncomplicated cases
Microscopic Lesions
- Fungal hyphae and spores in hair shafts (ectothrix or endothrix infection)
- Mild dermal inflammation
Diagnosis
Clinical Diagnosis
Based on characteristic circular lesions and species history.
Laboratory Diagnosis
- Wood’s lamp examination (fluorescence in some M. canis infections)
- Microscopic examination of hair/skin scrapings (KOH prep)
- Fungal culture (gold standard)
- PCR for species identification
Differential Diagnosis
- Mange (Sarcoptes, Demodex)
- Bacterial dermatitis
- Allergic skin disease
- Nutritional deficiencies
Summary for Practitioners
Fungal culture remains the most reliable diagnostic method, especially in subclinical infections.
Treatment
Topical Therapy
- Antifungal shampoos (miconazole, chlorhexidine combinations)
- Lime sulfur dips
- Enilconazole sprays
Systemic Therapy
- Itraconazole
- Griseofulvin (commonly used in small animals)
- Terbinafine (alternative option)
Environmental Treatment
- Disinfection of housing and equipment
- Removal of contaminated bedding
Summary for Practitioners
Successful treatment requires both animal therapy and environmental decontamination to prevent reinfection.
Control and Prevention
Hygiene Measures
- Regular cleaning and disinfection of animal housing
- Avoid overcrowding
Isolation
- Separate infected animals from healthy stock
Vaccination
- Available in some countries for cattle (T. verrucosum)
Biosecurity
- Control movement of animals between farms
- Quarantine new arrivals
Summary for Practitioners
Prevention is primarily based on hygiene, isolation, and environmental control rather than treatment alone.
Zoonotic Importance
Ringworm is an important zoonotic disease. Humans can be infected through direct contact with infected animals or contaminated environments, especially children and animal handlers.
Economic Importance
The disease causes economic losses due to reduced hide quality, treatment costs, decreased productivity, and zoonotic transmission risks in animal production systems.
Summary
Ringworm (dermatophytosis) is a contagious fungal skin disease of animals and humans caused by Microsporum and Trichophyton spp. It is characterized by circular alopecic lesions and is controlled through hygiene, antifungal therapy, and environmental management.
Home