Ringworm in Dogs
Symptoms, Causes, Treatment and Prevention

"All breeds and sizes of dogs can be infected by canine ringworm, which
also goes by the name dermatophytosis."

Ringworm in dogs is often misunderstood. It was once believed that ringworm infection was caused by a worm. We now know that ringworm is caused by a fungal infection of the skin or nails. Since ringworm is contagious and can be transmitted between dogs and people, it is important to understand the basics of this disease.

Ringworm in Dogs - Overview/Snapshot of the Disease

All breeds and sizes of dogs can be infected by canine ringworm, which also goes by the name dermatophytosis. Several different types of fungus can all cause ringworm and their spores can be found throughout our environment.

Healthy skin has many defenses against ringworm fungus, so unless a dog's immunity or protective skin barriers are compromised or he comes in contact with a large number or spores, he will probably not develop the disease.

Symptoms of Ringworm in Dogs

The symptoms of ringworm in dogs can look like many other types of canine skin disease, including pyoderma and mange. Dogs with ringworm can develop the following lesions:

• Hair loss (alopecia)
• Itching
• Flaky or crusty skin
• Pustules (i.e., pimples)
• Papules (small lumps in the skin)
• Mis-shapen and brittle nails

People with ringworm can develop a characteristic, raised ring-like lesion, but this is not often observed in dogs.

Causes of Canine Ringworm

There are three types of fungus that can cause canine ringworm infections. Microsporum canis is the most common cause of ringworm in dogs and the rest of the cases are caused by either Microsporum gypseum or Trichophyton mentagrophytes.

Infected animals, especially kittens, release large numbers of spores into in the environment and these are then able to infect other animals that come in contact with them.

Canine Ringworm Treatment

Because the symptoms of a dog with ringworm are the same as are seen with several other skin diseases, your veterinarian will need to run a few tests to determine the cause of your dog's skin lesions. Some types of ringworm fluoresce when lit by a black light.

Your veterinarian may use a Wood's lamp to see if the affected areas on your dog's coat, nails, or skin give off a green glow. Not every type of fungus that causes ringworm reacts in this way, so additional tests are often necessary.

Your vet may pluck hairs from around patches or hair loss and place them on an agar that encourages ringworm fungus to grow and helps in their identification. This test can take several weeks to complete, however. Skin scrapings to look for mites, cytology to look for bacteria and yeast, and sometimes even a skin biopsy are necessary to rule out other skin diseases.

Your veterinarian may also recommend testing other animals in the house even if they are not displaying any symptoms because they can be carriers for the disease and a source for reinfections if not treated.

Once a dog has been diagnosed with ringworm, treatment can begin. If your dog has a very long coat, your veterinarian may recommend that he is shaved. The use of anti-fungal shampoos, rinses, and ointments can eliminate the infection for many dogs.

In more severe cases, oral anti-fungal drugs might also be prescribed. Treatment often needs to continue for several months and should not be stopped until your veterinarian has run tests to confirm that your dog is no longer infected. Because infected animals shed many spores in their own environments, houses should be thoroughly vacuumed and disinfected to prevent reinfections or spread to other individuals in the home.

Prevention of Ringworm in Dogs

Isolating animals with ringworm and decontaminating areas that are known to contain a large number of spores is the best way to prevent the spread of ringworm. Because healthy dogs have many natural protective measures against ringworm, keeping your dog in good overall condition can also go a long way towards keeping your canine companion free of this disease.

Consulting Veterinarian: Jennifer Coates, DVM

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