Red Circular Rash on a Dog

The fungus Microsporum canis causes ringworm, a contagious skin infection characterized by a red ringed rash. The fungus thrives in humid climates and its spores can linger in dog bedding for up to 18 months. Ringworm's distinct round circle usually is enough for a diagnosis, but several fungi types cause ringworm, which can mimic the appearance of other skin rashes.

  1. Appearance

    • Ringworm lesions---blister-type bumps on the surface of the skin---commonly appear on the dog's head, legs, tail or feet. Lesions might be tiny or they can grow larger and cause hair loss around the affected area.

    Symptoms

    • The skin inside the rash ring can be scaly and itchy or nonirritating and round like a pimple or blister without a border.

    Diagnosis

    • A veterinarian can diagnose ringworm after scraping the scales or skin near the irritation and creating a culture using the medium indicated for ringworm, according to Vetinfo.com: "Once completed, the culture can be examined under a microscope and a diagnosis confirmed."

    Treatment

    • If the rash is limited to one area and the puppy or dog is healthy, treatment may not be needed; the affected spot will heal in about a month. However, if ringworm covers a large area or affects multiple areas on the dog's body causing pain, veterinarians will prescribe topical or oral antifungal treatments, Vetinfo.com states.

    Prevention/Solution

    • While ringworm occurs infrequently, dog owners should heed the signs of ringworm to avoid its spread. When applying topical medication, owners should wear latex or vinyl protective gloves to prevent spreading the infection; ringworm is called a zoonotic disease, meaning it can pass between dog and person.