CONDITION

Dermatophytosis (Ringworm)

Why this matters now

Dermatophytosis can affect dogs and cats of any age, though young animals, those with compromised immune systems, and certain breeds appear more susceptible. Cats, particularly long-haired breeds, are more commonly affected than dogs. The condition is frequently seen in animals from shelters, catteries, or multi-pet environments where close contact facilitates transmission. Some animals can carry the fungus without showing obvious signs, potentially spreading it to others.

Without intervention, ringworm lesions may gradually expand and new areas can become affected. In healthy animals, the condition can be self-limiting over several months, though this extended period allows continued environmental contamination and potential transmission to other animals and humans. The pattern of spread and severity can vary considerably between individuals based on immune response and the specific fungal species involved.

Signals & patterns

Early signals

Circular patches of hair loss

Classic ring-shaped areas where hair has fallen out, often with a slightly raised, scaly border and clearer centre.

Scaly or crusty skin

Affected areas typically show scaling, crusting, or a grey, powdery appearance where the fungus is active.

Broken or brittle hairs

Hair shafts in affected areas become weakened and break off, sometimes appearing stubbly rather than completely bald.

Mild itchiness

Some animals may show increased scratching or grooming of affected areas, though ringworm is often less itchy than other skin conditions.

Later signals

Spreading or coalescing lesions

Multiple patches may develop and can merge together, creating larger irregular areas of hair loss.

Nail bed involvement

In some cases, the fungus can affect the claws, causing brittleness, distortion, or discolouration of the nails.

Secondary bacterial infection

Damaged skin may become infected with bacteria, leading to more pronounced inflammation, discharge, or crusting.

Click to read about the biological mechanisms

How this is usually investigated

Diagnosing dermatophytosis requires specific testing because the clinical appearance can resemble other skin conditions. Confirmation of fungal infection guides appropriate management and helps assess zoonotic risk.

Wood's lamp examination

Purpose: Uses ultraviolet light to check for fluorescence that occurs with some strains of Microsporum canis.
Considerations: A useful screening tool when positive, but many ringworm infections do not fluoresce, so a negative result does not rule out the condition.

Fungal culture

Purpose: Hair and scale samples are placed on special growth medium to identify the specific fungus causing infection.
Considerations: Considered the gold standard for diagnosis. Results take 1-3 weeks, but positive identification confirms the diagnosis and species. Important for monitoring treatment success.

Microscopic examination (trichogram)

Purpose: Direct examination of plucked hairs under the microscope can reveal fungal spores around or within the hair shaft.
Considerations: Provides rapid results when positive but requires skill to interpret and may miss infections where fungal elements are sparse.

PCR testing

Purpose: Molecular testing can detect fungal DNA with high sensitivity, identifying the specific species involved.
Considerations: Faster than culture with good accuracy. May detect DNA from non-viable organisms, so context is important.

Skin biopsy

Purpose: Tissue sampling with histopathology can confirm fungal infection and assess the depth of involvement.
Considerations: Rarely needed for straightforward cases but may help when the presentation is unusual or other conditions are suspected.

Options & trade-offs

Management of dermatophytosis typically combines treating the infected animal with reducing environmental contamination. The approach balances speed of resolution against practicality and potential side effects.

Topical antifungal treatment

Medicated shampoos, dips, or localised applications help reduce fungal load on the skin and limit environmental shedding.

Trade-offs: Often used alongside systemic treatment for faster resolution. Labour-intensive with whole-body applications. May be sufficient alone for very localised infections.

Systemic antifungal medication

Oral antifungal drugs reach the infection through the bloodstream and are typically continued until cultures confirm cure.

Trade-offs: Generally effective but treatment duration is often prolonged (weeks to months). Some medications require monitoring for potential side effects. Stopping too early risks relapse.

Environmental decontamination

Thorough cleaning and disinfection of the environment helps eliminate spores and reduce reinfection risk.

Trade-offs: Essential for preventing spread to other animals and humans. Can be challenging in complex environments. Fungal spores are resistant and require specific cleaning approaches.

Isolation of affected animals

Keeping infected animals separate from others reduces transmission during the treatment period.

Trade-offs: Important in multi-pet households. Can be stressful for social animals. Duration depends on treatment response.

Clipping of hair coat

Removing hair from affected areas or the entire coat can reduce fungal burden and improve topical treatment penetration.

Trade-offs: Accelerates resolution when combined with topical treatment. Must be done carefully to avoid spreading spores. Contaminated hair must be disposed of properly.

Common misconceptions

Misconception:

"Ringworm is caused by a worm"

Reality:

Despite its name, ringworm is a fungal infection, not a parasitic worm. The name derives from the ring-shaped appearance of skin lesions in humans.

Misconception:

"Only visibly affected animals can spread ringworm"

Reality:

Some animals, particularly cats, can carry and shed fungal spores without showing obvious lesions. These asymptomatic carriers can be a source of infection for other animals and humans.

Misconception:

"Once the lesions look better, treatment can stop"

Reality:

Fungal cultures rather than appearance should guide treatment duration. The infection can persist below the surface even when hair regrowth begins, and stopping treatment prematurely often leads to relapse.

Documenting the location and progression of any lesions with photographs can help track response to treatment. Being aware of the zoonotic potential is relevant for all household members, particularly children or immunocompromised individuals who may be more susceptible. Understanding that resolution typically takes weeks rather than days helps set realistic expectations for the treatment period.

Last reviewed: Invalid Date · ConciergeVet Clinical Team