Ringworm (Dermatophytosis) in Dogs

Key Takeaways

Ringworm, also known as dermatophytosis, is a fungal infection of the skin, hair, or nails in dogs.

• Ringworm is a common and highly contagious disease which presents with patches of hair loss alongside red and crusty lesions

• Skin patches vary in size and number, often developing around the head and forelimbs, and are sometimes itchy

• Ringworm lesions are most common in dogs less than a year old, and senior or unwell dogs

• Diagnostics include physical examination, fungal culture, and microscopy

• Treatment options include topical and oral antifungal medications for a minimum of six weeks

• Environmental decontamination reduces reinfection and hastens recovery

• Prognosis is good, some cases are self limiting and more persistent cases normally respond well to treatment

Ringworm can pass from pets to in-contact humans, particularly young children

A Closer Look: What is Ringworm in Dogs?

Ringworm is a common and highly contagious zoonotic disease found in many mammalian species. Although widespread, the presentation is generally mild and responds well to prompt treatment. Dogs with skin lesions benefit from prompt veterinary attention.

Risk Factors

Symptoms vary depending on the severity of the infestation, immune response of the host, and the fungal species present. Microsporum spp. are commonly transmitted via cats whereas Trichophyton spp. are more commonly found in wildlife such as rodents. 

Small dogs such as Jack Russell Terriers and Fox Terriers may have a genetic predisposition to contracting ringworm. Senior dogs and dogs with underlying immunocompromisation are also at higher risk.

Possible Causes

Ringworm is an infection resulting from a variety of different fungal species. Microsporum canis and Trichophyton spp. are the most common species found in dogs. Transmission occurs via direct or indirect contact with fungal spores found on other animals or in the environment.

Main Symptoms

Symptoms of ringworm infection are commonly found on the head and forelimbs and may include:

• Areas of hair loss

• Skin lesions, which may be crusty, red, and/or sore

• Stunted or abnormal nail growth

Occasionally, ringworm lesions may be itchy, but not always.

Testing and Diagnosis

Investigation of ringworm involves:

• Physical examination

• Fungal culture

• Microscopy

• Biopsy

• Woods lamp testing (examination of the skin under UV light)

Steps to Recovery

Treatment options include:

• Antifungal medication: Topical or oral depending on extent of the lesions

• Clipping hair from lesions to reduce reinfection

• Environmental decontamination: removal of hair and dandruff from the environment; disinfection of the environment such as bedding and grooming implements 

Ringworm is a persistent infection and sometimes takes weeks or months to resolve. Fungal infection of the nails is particularly persistent. Cases often require repeat testing to confirm resolution and treatment continues for several weeks after the skin lesions resolve.

Prognosis with appropriate treatment is good but cases sometimes require extensive therapy. Dogs with underlying immune system disorders are more susceptible to fungal infection and sometimes respond less well to treatment.


Ringworm is highly contagious to other dogs as well as humans and other mammals. Prevention involves reducing contact with fungal spores by controlling ringworm in the environment and isolating infected cases (confirmed or suspected).

Is Ringworm Common in Dogs?

Ringworm is a common fungal infection in dogs. It is especially prevalent in dogs under 1 year old, old dogs, or dogs with concurrent disease or a poor immune system.

Typical Treatment

• Antifungal medication

• Clip hair from lesions to reduce reinfection

• Environmental decontamination

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