How To Treat Ringworm

By: Carol S. Hillhouse, DVM, DABVP

TVMA Member
Panhandle, TX

Published March 2016

Ringworm is a skin infection caused by a group of fungi. In fact, it is not caused by worms at all! Fungi reproduce by producing sporesa cell made by some plants that is like a seed and can produce a new plant, and it takes skin contact with a spore to cause an infection. Infected animals are continuously shedding spore-covered hairs. The ringworm spores are exceptionally hardy and can live for one year or more in the environment. Therefore, a potential victim does not have to come in direct contact with an infected animal to become infected; it just needs to come in contact with an infected hair. Some animals are asymptomatic carriersorganism that has contracted an infectious disease, but who displays no symptoms, which means they have ringworm but do not show signs of a skin problem; however, their shed hairs carry the ringworm spores, which can infect others.

Ringworm is contagious to people and animals. It is especially a problem for those with a poor immune system. That means the very young or elderly, those undergoing chemotherapy treatment and transplant patients are most at-risk.

Diagnostic Testing

In animals, ringworm frequently looks like a dry, scaly patch of skin, which may or may not be itchy, but it can have all sorts of different appearances. Veterinarians use appearance, cultures and sometimes biopsies to help diagnose ringworm infections. In approximately 50 percent of the cases, the most common ringworm fungus, Microsporum canis, will fluoresce the hairs a green color under an ultraviolet lamp. The fungus can be grown or cultured, which will confirm the infection and identify the type. The culture also can help determine whether an animal is a carrier without clinical signs. Knowing the type may determine the source of infection. Fungi grow slowly though, and culturing may take several weeks.


It is best to treat both the pets and their environment. Infected pets may require oral medication and topical treatments. Examples of oral medications used for ringworm include terbinafine, itraconazole, fluconazole and griseofulvin. Selection often depends on availability, price and the age of the patient, but all of these treatments inhibit fungal reproduction. Appropriate topical treatment with medicated shampoos, creams and dips have the added benefit of killing the fungus on the hairs so the dropped hairs will not be contagious.

Because infected animals are constantly shedding hardy spores, environmental disinfection is just as important as treatment of the pet. The infected pet should be isolated to one room, preferably without carpet. Unfortunately, few products are effective in decontaminating the environment, and the single most important aspect is vigorous repeated vacuuming. Remember to discard the bag or clean the canister! Diluted bleach (a ratio of 1-to-10 with water) will kill most of the spores and should be used on any surface where it is safe. Steam cleaning and a Swiffer® or similar product may also be helpful to pick up infected hairs.

Continue treatment for one to two months, and do not discontinue until the pet’s cultures test negative. Stopping when the pet looks well often leads to recurrence of disease.

If the outbreak is still going strong after a couple of months, your veterinarian can look at alternatives and determine whether changes need to be made. If humans become infected, a physician should be contacted for treatment. Veterinarians cannot make recommendations for human infections, even if that infection comes from a pet.


Dr. Carol Hillhouse owns two mixed animal practices in the Texas Panhandle: Carson County Veterinary Clinic and High Plains Animal Hospital.

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