Despite its name, ringworm isn't actually a worm. It's a fungal infection of the hair, skin, and nails that affects all mammals, including dogs, cats and people. Different species of fungus cause ringworm, but Microsporum canis is the most common culprit in dogs.
Dogs contract ringworm through contact with infected soil or the hair of an infected animal. The fungus invades hair follicles, causing inflammation and hair loss. Ringworm can pass between people and pets, and children are more susceptible than adults.
Risk factors and detection
Ringworm occurs most often in young dogs. Dogs living in large groups—in kennels, for example—also are at greater risk.
If your dog has ringworm, you may notice circular areas of hair loss with scaly skin in the middle and a red ring at the edge. The fungus can affect only a few areas—or the entire body. In dogs, it primarily affects the face, earflaps, paws, and tail. Ringworm alone isn't itchy, but a secondary bacterial infection often causes dogs to lick or scratch the affected areas.
Other skin diseases, such as mange, can cause similar signs, so consult your veterinarian for an accurate diagnosis. Your veterinarian can use an ultraviolet light as a quick screening test—if present, the fungus glows fluorescent green. This test, however, is not conclusive. The best diagnostic test is a fungal culture, which involves harvesting a few hairs and scales from the affected area. Your veterinarian will know the culture results within a few days. Meanwhile, you may begin treatment immediately if the doctor suspects ringworm.
Treatment and prevention
Most cases of mild ringworm clear up spontaneously, but veterinarians recommend treatment to prevent the spread of infection. Your first step: Clip longhaired dogs to expose the affected areas. Then you'll apply topical antifungal medications, shampoos, or dips. The condition should clear up in about four to six weeks.
More severe cases or cases that don't respond to topical therapy require oral antifungal medications, such as griseofulvin or ketoconazole. One warning: Both drugs can cause serious side effects, including gastrointestinal upset, bone marrow suppression, appetite loss, and liver disease. If the veterinarian prescribes either of these drugs, you and your doctor must monitor the dog closely. And don't give these drugs to pregnant females because they can cause birth defects.
Thoroughly cleaning your dog's environment also is crucial. Clean hard surfaces with a 10 percent solution of bleach in water, discard the dog's bedding, vacuum the carpets regularly, and sterilize grooming equipment with bleach. Always wear gloves when handling your infected dog, and keep children away from infected dogs until treatment is complete.
Some environments are difficult to clean, and reinfection may occur. Treating dogs in multiple-pet households is also difficult because the disease spreads easily. So be sure to treat any household pets who could be infected.
