Ringworm (Dermatophytosis) in Dogs

Overview of Canine Ringworm

Ringworm is a contagious fungal infection of the skin, caused by Microsporum canis. It is not caused by a worm. It is spread from person to person, from animal to person, or indirectly from contaminated objects or the soil. The associated spores can live for years in some conditions. Ringworm infects three sites: scalp, body and nails.

Ringworm is considered a “Zoonotic” disease meaning that it can be transmitted from animal to person.

There are several organisms that can cause ringworm including Microsporum canis, Microsporum gypseum and Trichophyton mentagrophytes.

Ringworm is typically seen in young dogs. Dogs with pre-existing skin disease or trauma are more likely to become infected. Diseases or medications that suppress the immune system generally render that dog more susceptible to ringworm.

Predisposing factors may include high stress situations (such as shelters), stress, poor nutrition, cancer, immunosuppressive drug therapies and other diseases or medications that suppress the immune system. Young animals appear to be predisposed. Some pets may be resistant to infection and other may remain as carriers with no clinical signs.

Typical lesions are circular areas of hair loss (alopecia) on the hair coat; however, any change in the hair coat and/or skin may be consistent with ringworm. The affected skin often appears scaly and inflamed. Some dogs suffer from severe skin disease while others have minor lesions or even none at all.

What to Watch For

• Circular areas of hair loss (alopecia)
• Scaly and inflamed skin
• Itching in some cases

Diagnosis of Ringworm in Dogs

Ringworm often looks similar to other skin diseases, so it is difficult to diagnose based on skin appearance alone. Your veterinarian will run diagnostic tests to confirm the presence of the fungus. Some of these test may include:

• Laboratory tests to include a complete blood count, biochemical profile, and urinalysis if immune suppression is a suspected underlying cause of the ringworm.
• A fungal culture to provide positive identification .
• Woods lamp examination. If the area fluoresces under the light, ringworm is suspected. However, culture is still strongly recommended. A negative fluorescence does not rule out ringworm, as several species of the ringworm do not fluoresce.
• Microscopic examination of hairs.

Treatment of Ringworm in Dogs

The treatment for ringworm can be both frustrating and expensive, especially in a multi-pet household. Treating both the dog and the environment are of equal importance. Many dogs will resolve an infection spontaneously over several months, but treatment generally expedites cure and helps reduce environmental contamination. Nevertheless, some infections can persist.

Vaccines for ringworm are available, but are only used in addition to treatment.

• Systemic treatment. There are several different oral medications available. Griseofulvin is the most commonly prescribed, and it needs to be given with food. Your dog will also have to have her blood count monitored by your veterinarian to watch for possible bone marrow suppression (low white blood cell, red blood cell, and platelet counts) as a side effect. If there is a possibility of pregnancy, alert your doctor at once, as certain medications may be contraindicated. Other drugs used to treat ringworm include Itraconazole, Ketoconazole, and Lufenuron. Lufenuron should not be used as a sole therapy. Test results suggesting its effectiveness are controversial and it has not been proven as an effective sole therapy.
• Topical treatment. Anti-fungal creams and shampoos are important in reducing environmental contamination. This usually includes clipping the hair of affected dogs and dipping in lime sulfur or antiseptics. Twice weekly topical therapy with chlorhexidine 2% shampoo followed by 0.2% enilconazole rinse has been effective in some pets.
• Home Cleaning. It is recommended that the pet’s environment be thorough cleaned. Spores can live for years in some situations. Unnecessary items should be destroyed or disposed of. The environment can be cleaned with a 05% sodium hypochlorite solution (Bleach diluted to 1:20 solution), which can be used to clean washable items.

Home Care and Prevention of Ringworm

At home, give your dog the prescribed medication as directed by your veterinarian. Return for follow-up appointments as directed. If side effects develop, early detection can reverse these effects. Culturing your dog for ringworm is the only true means of monitoring response to therapy.

Due to the contagious nature of ringworm to humans, care should be taken to wash hands thoroughly after handling the dog. Immunocompromised individuals should exercise extreme caution and may want to consider not handling the dog until fully recovered.

Extreme care can help prevent ringworm disease. When bringing a new dog into a household, use a quarantine period and do a fungal culture to test for the presence of the fungus.

You can also employ preventative treatment of exposed animals.