Ringworm is an infection by a fungus that most often affects the hair, nails, and superficial layers of the skin. The most commonly noted fungal types seen in cats and dogs are Microsporum canis, Trichophyton mentagrophytes, and Microsporum gypseum.
Animals can come into contact with infective fungal spores in the indoor or outdoor environment. Contaminated soil is a common source of infection, as are other animals infested with ringworm. Not all animals that are exposed to fungal spores develop a fungal infection, and if an infection does occur, the dog or cat may not show clinical signs of the disease but instead serve as asymptomatic carriers.
The classic clinical sign of ringworm is the circular patch of hair loss with a red ring of inflammation. However, not all animals infected by ringworm will have this type of lesion. In fact, because the symptoms of this disease can vary greatly, ringworm should be considered as a possible cause of skin disease in any eruptive skin disorder.
Although most healthy dogs and cats can rid themselves of a fungal infection on their own, some cases can be very frustrating to cure. The asymptomatic carrier state can complicate matters. Since the presence of disease is hidden in these cases, owners will not know to take precautionary measures to protect against the spread of infection. Animals that do not respond to treatment, especially those living in multiple-cat households, should be referred to a veterinary dermatologist or specialist.
