Dermatophytosis in Animals (Ringworm) 

Dermatophytosis in Animals (Ringworm) 
By Dr. Supawan Sriwiset, DVM

Dermatophytosis in animals is a skin disease caused by a group of fungi known as Dermatophytes. When an animal is infected, it leads to inflammation of the superficial layers of the skin. Key clinical signs include hair loss (alopecia), itching (pruritus), and red, inflamed skin.

There are over 40 species of dermatophytes capable of infecting both animals and humans. These fungi utilize keratin found in the skin, hair, and nails as a food source, multiplying and spreading from one area of the body to another. The severity of symptoms depends on the specific fungal species and individual animal factors. Furthermore, dermatophytosis is zoonotic, meaning it can spread between animals or from animals to humans.

This condition is frequently encountered in veterinary practice, especially in dogs, cats, and rabbits. The primary causative agents in dogs and cats are Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes, with Microsporum canis being the most common.

Etiology (Causes)
Dermatophytes belong to the Phylum Deuteromycota and are classified into three main genera: Epidermophyton, Microsporum, and Trichophyton.

Pathogenesis (How the disease develops)
Dermatophytes are categorized into three groups based on their preferred habitat:

Geophilic (soil-loving): Typically found in soil; can cause infection in both humans and animals.
Zoophilic: Found on the skin and fur of animals; primarily causes disease in animals and can be transmitted to humans.
Anthropophilic: Found on human skin; primarily causes disease in humans and rarely affects animals.
Transmission from animals to humans mostly occurs through direct or indirect contact with infected animal hair or fungal-contaminated skin dander.

The infection enters the animal's skin via fungal spores called arthrospores. These spores enter through wounds or damaged areas of the skin. Once inside, the fungus multiplies within the keratin of the stratum corneum (the outermost layer of skin), hair, or nails. The fungi produce an enzyme called keratinase, which triggers an inflammatory response at the site of infection, resulting in clinical signs such as redness, inflammation, and hair loss.

Predisposing Factors & At-Risk Animals
Very young or very old animals.
Sick animals with weakened health, stress, or immunocompromised states.
Animals with long hair, dirty coats, or damp/moist fur.
The "Inoculum Load" (the amount of fungus exposed to), such as contact with an infected animal or an environment heavily contaminated with spores.
Clinical Signs
Infected animals may be symptomatic or asymptomatic carriers, depending on the factors mentioned above. Common symptoms include:

Hair loss (alopecia) or broken hair shafts.
Itching and scaling (dander).
Circular lesions: Hair loss often appears in a circular pattern. The edges are typically raised, red, inflamed, or crusty.
Secondary bacterial or yeast infections may also be present.
Diagnosis
Wood’s Lamp Examination: Used primarily to detect Microsporum canis. Infected hairs will show a fluorescent apple-green glow (used as a preliminary screening).
Microscopic Examination (looking for spores or hyphae):

Trichogram: Microscopic evaluation of plucked hairs.
KOH Preparation: Using Potassium Hydroxide to dissolve keratin, making fungal spores and hyphae clearly visible.
Fungal Culture: Samples of hair or scales are placed on specific culture media. Growth usually takes 1–3 weeks. Once a colony grows, it is examined under a microscope to identify the specific fungal species.
Treatment
Treatment options vary based on the severity of the disease:

Mild cases: May only require topical treatment, such as antifungal ointments or medicated shampoos.
Severe cases: If the infection is widespread or severe, oral systemic medication is usually required alongside topical therapy.
Duration: Treatment typically lasts at least one month or longer, depending on severity.
Note: Owners must identify the source of the fungus to prevent reinfection.
Examples of Medications:
Medicated Shampoos: Containing Miconazole or Enilconazole.
Topical Creams or Sprays: Ketoconazole cream/spray or Miconazole spray.
Oral Antifungals: Imidazoles (Itraconazole, Fluconazole, Ketoconazole), Griseofulvin, Lufenuron, or Terbinafine.
Environmental Disinfectants (to eliminate spores):

Bleach (diluted 1:10).
Enilconazole solution (0.2%).