Ringworm is a fungal infection that can affect the skin, hair, or nails of dogs and humans. In dogs, 70% of ringworm cases are caused by the fungus Microsporum canis, 20% by the fungus Microsporum gypseum, and 10% by Trichophyton mentagrophytes. The infection spreads through direct contact with the fungus, which can happen when a dog comes in direct contact with an infected animal or person or touches a contaminated object like a couch, comb, food bowls, bedding, or carpet. The fungal spores responsible for the spread can remain viable for up to 18 months and typically spread through shedding or breaking of infected hairs.

Symptoms of ringworm in dogs include circular areas of hair loss throughout the body, which may start to heal in the center as they enlarge, creating a patchy appearance, and may become inflamed or scabbed. The affected hair shafts are fragile and easily broken. In most cases, there are several patches scattered throughout the body. Ringworm is not a life-threatening disease, but it is very contagious and does require the intervention of a veterinarian.

The most accurate method for diagnosing ringworm in dogs is by a culture of the fungus in a laboratory. To do this, samples of hair and skin scrapings are taken from the dog. A positive culture can sometimes be confirmed within a couple of days, but in some cases, the fungal spores may be slow to grow, and culture results can take up to three weeks. The most common way to treat ringworm in dogs is to use a combination of topical therapy (application of creams, ointments, or shampoos) and systemic therapy (administration of anti-fungal drugs by mouth). For treatment to be successful, all environmental contamination must be eliminated.

Ringworm is highly contagious between dogs and humans, so it’s important to take appropriate steps to minimize the risk of transmission. Preventive measures include keeping your dog clean and dry, avoiding contact with infected animals, and washing your hands after handling an infected dog.