Ringworm in Dogs

Dog with ringworm on nose
Sarah Salmela / Getty Image

Ringworm derives its name from the round "worm-like" rash seen on infected human skin. However, ringworm is not a worm at all, but rather a zoonotic fungus that can spread back and forth from dogs to humans (and vice versa). Often contracted through spores that reside in the soil, ringworm can be found anywhere on a dog's body, resulting in skin lesions and discomfort. Luckily, most cases respond well to a treatment of antifungal medicines. This medicine course, combined with a thorough washing of bedding and toys, may be all that is needed to heal your pet and prevent transmission to family members.

Symptoms of Ringworm in Dogs

Classic ringworm lesions present on animals as patchy areas of hair loss and scaliness. These lesions can appear on a dog's head, ears, paws, and limbs. A ringworm infection on a dog may simply look like a bald spot, with very little inflammation or redness—and it's not usually itchy. Mild cases in "asymptomatic carriers" may not even show at all. Whereas, severe cases can spread all over the body, resulting in inflamed, scabby lesions. Ringworm infections of the paws can lead to a nail infection, where claws become brittle and broken.

In humans, ringworm presents quite differently, depending on the type of fungus and the location of the body. Most commonly, the lesions are red, raised, itchy, and sometimes scaly. If lesions are found on both your pet and yourself or a family member, treatment will be needed to prevent further contagion.

Causes of Ringworm

Since the ringworm fungus resides in the soil, a digging dog encounters it regularly. However, not all animals will contract the fungus simply from contact. The age of your dog (puppies are more prone to infection), its immune status, and grooming habits all affect the rate of transmission. In both people and dogs, those with suppressed immune systems are most at risk.

Ringworm transmission can also spread when your dog comes into contact with an infected animal or its bedding, toys, brushes, saddles, and another tack. Even home furnishings and rugs can harbor infection. And fungal spores can lay dormant on a variety of surfaces—like combs, brushes, and food bowls—for many months.

Treatment

A quick in-office test called the "Wood's lamp examination" uses an ultraviolet light in a darkened room to see if the affected area will fluoresce. However, not all ringworm infections will fluoresce and other rashes may cause a false detection. For a definitive diagnosis of ringworm, a fungal culture may be needed, which involves collecting hair and skin scrapings, and then watching for fungal growth in a lab. This process can take several days and up to a few weeks.

Ringworm treatment varies with the severity of the infection. Mild cases call for a topical treatment which often involves washing your dog with an anti-fungal shampoo twice weekly. Other topical remedies include medicated ointments or creams applied to the lesions. A vet may recommend shaving the areas in question or cutting your dog's hair short to aid in the treatment.

Advanced cases call for prescription oral medications, usually in addition to topical treatment. Oral medicine, however, is generally reserved for severe or chronic infections, since it's expensive and can initiate a slew of side effects, including nausea, vomiting, diarrhea, and loss of appetite. Treating severe ringworm cases involves a six-week (minimum) protocol, one that, if stopped too soon, may spark a recurrence of infection. After that, a ringworm culture is ordered again, and two negative tests assure riddance of the infection.

Ringworm in the Environment

In addition to treating the dog, pet owners must also treat their environment, as ringworm can survive (under the right conditions) for up to 18 months. A basic protocol looks something like this: Confine your contaminated pet to one room. Vacuum rugs and floors deeply, taking care to dispose of vacuum bags or canisters in an outside garbage can. Dispose of rugs and carpets that are specific to pet use. Wash all bedding and toys with a bleach solution. Or better yet, dispose of them and replace them. Disinfect all surfaces with soap and water, followed by a diluted bleach solution (1-part bleach to 10-parts water).

Preventing Ringworm

You can't restrict a dog from romping in the woods and rolling on the ground. But since your dog's favorite places may be ringworm infested, impeccable hygiene will prevent infection. Launder all dog beds and mats regularly in hot water and detergent, get on a consistent grooming schedule, and vacuum any common areas (or anywhere your dog hangs out) at least once a week. Also, wash dog toys monthly in a diluted bleach solution.

For additional environmental ringworm tips, please see the University of Guelph's Worms & Germs site.

This article is provided for informational purposes only. If your pet shows any sign of illness, please consult a veterinarian as quickly as possible.