Ringworm is a skin infection caused by fungus in the environment. This contagious skin disease can affect dogs, humans, and other animals. Signs of ringworm include scaly, red, itchy skin lesions. Fortunately, most cases respond well to medical treatment and environmental decontamination, which also help prevent the spread of ringworm to people and pets.
What Is Ringworm?
Ringworm is a common term for dermatophytosis, a fungal infection of the skin that causes hair loss, redness, and scaly skin. It is a zoonotic disease, meaning that it can be spread between dogs and humans. Despite its name, ringworm is not actually a worm or parasite of any kind. The reason for the name is that the fungus causes a ring-shaped skin lesion that has a worm-like appearance, especially visible on areas of sparse hair coverage.
Symptoms of Ringworm in Dogs
Ringworm symptoms are limited to the skin and paws of infected dogs and can be uncomfortable. These symptoms are usually recognizable before the infection has become too severe.
In dogs, ringworm lesions typically look like patchy areas of hair loss and scaliness. Lesions typically develop on the dog's head, ears, paws, and limbs, but can occur on any other area of the skin.
Ringworm varies in severity. In some cases, lesions can become red, irritated, and itchy. Ringworm on the paws can cause nails to become brittle and break easily. In mild cases, hair loss may be the only noticeable sign.
Ringworm in humans often presents quite differently, but this depends on the type of fungus and the location of the body. Lesions are usually red, raised, itchy, and sometimes scaly. Most ringworm lesions in humans will have a ring-like appearance.
Causes of Ringworm
There are several species of dermatophyte fungi found in the environment. Dermatophytes are often found in soil, surfaces, objects, and on other animals. Animals and humans come into contact with them regularly, but the fungi do not affect healthy skin. However, mildly irritated skin is easily infected by dermatophytes. This includes skin that has been recently shaved, scraped, scratched, or otherwise inflamed. Dogs with sensitive or compromised immune systems are more easily infected with ringworm. Puppies are vulnerable due to their immature immune systems.
- Ways dogs might encounter dermatophyte fungi include:
- Spending a lot of time outdoors
- Coming into contact with affected animals
Dermatophytes can also live on bedding, toys, bowls, and other items, so they pass easily among animals in the same home. Fungal spores are fairly hardy in the environment and can survive for several months.
Diagnosing Ringworm in Dogs
A veterinarian's physical examination is necessary to evaluate the skin and the overall condition of the dog. The vet may use a tool called a Wood's light to look for ringworm lesions. This tool contains ultraviolet light that causes some ringworm lesions to glow neon green when shined on the skin in a dark room. However, some types of lesions will not appear during this exam and further tests may be necessary.
The vet may take a sample of hair and skin to look for dermatophytes under a microscope, or a fungal culture may be necessary. A fungal culture is one of the best ways to definitively diagnose ringworm. This is done by putting a sample on a culture medium and placing it in a dark area in an attempt to grow fungal spores. If growth is seen, the sample is analyzed microscopically to identify the type of fungus. Complicated cases may require a skin biopsy.
Ringworm infections eventually resolve on their own in an immune-competent animal, but treatment can shorten the course of the disease and prevent it from spreading to other humans and other animals. Without treatment and environmental disinfection, ringworm may continue to recur and be passed between members of the home.
Treatment of ringworm may involve the use of prescription oral medication and topical treatments. Mild cases may be only treated topically at first with medicated shampoos or dips. Topical creams or sprays may be used concurrently. Baths or dips are usually recommended twice per week. Creams and sprays are usually applied two or more times a day.
Oral anti-fungal medications are typically used in moderate to severe cases and may need to be administered for six weeks or longer. Potential side effects include nausea, vomiting, diarrhea, and loss of appetite. Follow-up fungal cultures are necessary to determine if the treatment has been successful. It's important to continue medications as recommended until your veterinarian says treatment is complete. Otherwise, the ringworm infection is likely to recur.
Environmental decontamination is an important part of treatment and will reduce the likelihood of recurrence. Ringworm is hardy and can survive in the environment for many months, continuing to reinfect household members. Cleaning will not eliminate every spore, but it can significantly reduce the amount in the environment.
The home should be cleaned and vacuumed thoroughly several times per week, then disinfected. Disinfection should be done with bleach wherever possible. Clean toys and bowls with soap and water, then disinfect with a diluted bleach solution. Steam cleaning can disinfect carpets, rugs, and upholstery. Wash bedding and other materials with bleach as well.
Dogs with ringworm should be confined to one room of the house during treatment. Other pets should not have access to this room. The room should be cleaned twice a week during treatment, then thoroughly disinfected after recovery.
Prognosis for Dogs with Ringworm
Ringworm responds well to rigorous, persistent treatment, allowing dogs to return to full health. The trouble with ringworm is how hardy and contagious it is, meaning it can continue to reinfect your dog or other members of your household in a vicious, itchy cycle that requires vigilant attention to break.
How to Prevent Ringworm
There's no way to fully prevent your dog's exposure to ringworm because it naturally occurs throughout the environment. However, you can reduce your dog's risk of ringworm infection through good hygiene and common sense. Take good care of your dog's skin and overall health. Groom your dog regularly. Visit the vet for routine wellness check-ups as recommended. Keep your dog's bedding and toys clean and dry; wash beds regularly, and replace or clean toys as needed. Clean your home regularly, making sure to vacuum, mop, and wipe down your dog's areas in the process. Don't allow dogs with skin conditions or open wounds to play outside. Contact your vet for treatment of skin irritations as soon as possible.
Is Ringworm Contagious to Other Animals?
Ringworm is very contagious and can easily be passed back and forth between household members of all species. Medical attention is necessary to prevent continued transmission. Contact your veterinarian if your pet has signs of ringworm.
Is Ringworm Contagious to Humans?
Ringworm is contagious and can easily spread to human skin, especially in areas where the skin is scratched or abraded. Contact a physician if any humans in your home are affected because all members of the household will require treatment to stop transmission and facilitate healing.
Dermatophytosis in Dogs and Cats. Merck Veterinary Manual
Symptoms of Ringworm Infections. Centers for Disease Control and Prevention