Ringworm in Dogs

Ringworm (also known as dermatophytosis) is a contagious fungal infection of the skin, caused by Microsporum canis, Microsporum gypseum (from soil), or Trichophyton mentagrophytes (from rodent contact) fungi. It is a parasitic fungal infection that affects the skin, hair and/or nails (claws).  

The term "ringworm" is a misnomer, since the condition is caused by fungi of several different species and not by parasitic worms. In pets, the fungus responsible for the disease survives in skin and on the outer surface of hairs.

Dermatophytosis is a zoonotic disease which can spread from animals to persons. It can also spread from person to person, from animal to person, or indirectly from contaminated objects or the soil. The associated spores can live for years in some conditions. Ringworm infects three sites: scalp, body and nails.

Ringworm is typically seen in young dogs. Dogs with pre-existing skin disease or trauma are more likely to become infected. Diseases or medications that suppress the immune system generally render that dog more susceptible to ringworm. 

Clinical signs of dermatophytosis include:

Alopecia (hair loss)

Circular and patchy skin lesions, raised plaques on the skin

Furunculosis on legs and paws (acute abscess of a hair follicle due to infection by Staphylococcus)

Facial folliculitis (inflamed hair follicles)

Nailbed and nail infection

Irritated, scaly skin


Skin redness

Darkened skin (hyperpigmentation)

Poor hair coat

Other indications of dermatophytosis that are readily apparent on the skin are raised, rounded, knotty (nodular) lesions known as granulomatous lesions, or boils, and raised nodular lesions that frequently ooze (kerions), the result of ringworm infection. There may also be inflammation of the claw folds — the folds of skin bordering the nail, and medically referred to as paronychia.

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