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What is Ringworm in Dogs and Ringworm in Cats

photo of a black and white dog with ringworm infection on the face. ringworm on dogs.

What is Ringworm in Dogs?

Ringworm is the common name for a fungal infection that affects superficial layers of hair, skin, and nails. It is common in all domesticated animals, like dogs and cats, and can be transmitted from animal to human and vice versa. It is called ringworm due to the appearance of the lesion, which is often ring-shaped and red but not always, so the name is a little misleading. The infection is also not caused by a worm.

What Causes Ringworm in Dogs?

Ringworm is caused by a group of fungi known as dermatophytes. The disease is medically referred to as dermatophytosis. The most common dermatophytes that affect dogs are Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes, which can also be transmitted to humans.

What are the Clinical Signs of Ringworm in Dogs?

Ringworm in dogs often affects the hair follicles, causing them to break – this is when the skin gets infected and the ring lesion forms. If not treated, the fungi multiply, and the lesion can become irregularly shaped and spread over the dog’s body.

Some clinical signs are

  • alopecia (areas of hair loss)
  • redness of the skin
  • itchiness

Because the lesions are itchy, it is easy for the fungi to spread to the snout and nails. In the nails, the infection is called onychomycosis and causes the claws to become rough, brittle, and broken.

While some dogs will present all symptoms, others can present only one or no symptoms at all. These are called “asymptomatic carriers”, as they don’t develop any clinical signs, but they can carry the fungi and spread it to other animals and humans. This is especially problematic if the infected dog lives somewhere like a kennel or a shelter.

Ringworm is highly transmissible by direct contact with infected animals, or by indirect contact, like touching bowls, brushes, bedding, or carpet that were used by infected animals. The fungus can remain dormant for over 18 months in the environment, which makes this type of skin infection particularly hard to get rid of.

Once infected, a dog may take seven to fourteen days to show any lesions. Some cases take up to 21 days before any signs develop. Others, like mentioned, can be asymptomatic carriers that spread the infection to other animals and humans.

illustration of a dog with a sore on their head, missing fur on the back and crusty paw. ringworm in dogs.

What are the Diagnostic Tests for Ringworms in Dogs?

There are three ways to reach a diagnosis for ringworm in dogs. A veterinarian can choose one or more of these methods.

Cytology is when the veterinarian collects a few hair samples and possibly a scrape of the affected skin for analysis under a microscope. This method is not super accurate as the collected sample may not show the fungus and the disease can be misdiagnosed.

woodslamp test being done on a small dog sitting on an examining table. ringworm on dogs.

Wood’s Lamp is a quick test where the Veterinarian examines the hair and skin of the dog under ultraviolet light. Most cases of M. canis fungi will glow with a yellow-green fluorescence when observed in a dark room with ultraviolet light. However, M. canis doesn’t always glow. M. gypseum and T. mentagrophytes do not glow under a Wood’s Lamp. Although this method is acceptable, it is not always very reliable to diagnose ringworm.

Culture is the preferred and most reliable method of diagnosis for ringworm in dogs. A culture can be confirmed as fast as a couple of days in some cases. However, a culture cannot be regarded as negative for at least a month, as some cultures may be slower to grow.

Because there are multiple kinds of ringworm that can cause alopecia in dogs, a veterinarian is the most qualified person to examine your dog and rule out any other cause.

What are the Treatment Options for Ringworm in Dogs?

Most veterinarians opt to treat ringworm on dogs with a combination of topical (antifungal sprays and ointments) and oral (antifungal drugs) treatments. Both treatments must be given for the dosage period that the veterinarian prescribes. Also, the environment must be decontaminated to prevent reinfections.

Do not stop any treatment prescribed by your veterinarian, as it can cause the infection to reoccur.

Is There a Ringworm Treatment for Cats?

As mentioned, ringworm in cats is one skin disease that is hard to get rid of. Because it is highly transmissible by direct and indirect contact.

Once cat ringworm is diagnosed, the infected pet must be isolated from other animals in the household and from humans. Ideally, beds, carpets, and bowls must be replaced. If this is not possible, they must be thoroughly cleaned. The environment must also be cleaned properly.