Ringworm affects the hair and hair follicles. It is highly contagious and can infect not only dogs, but also cats and humans. It is therefore important to take precaution when handling a dog with ringworm to avoid being infected.
Children are especially susceptible and should not be allowed to handle pets with ringworm.
Canine ringworm usually affects puppies and young adult dogs. In most cases, the fungus responsible is called Microsporum canis, although there are a few other species that can cause this skin disease in dogs.
The ringworm fungus strives in hot and humid climates. But, for some reason, most cases of ringworm occur not in the summer. Instead they occur in the drier and cooler seasons of autumn and winter.
Transmission of this fungal disease is by direct contact with an infected animal, and through spores of the fungus in the soil and air.
Spores from an infected dog can be shed into the living environment (e.g. carpets, bedding, furniture. They can also attach to grooming tools (combs, brushes) and toys. The spores can live in the environment for over 18 months.
The good news is, it is quite infrequent for dogs to be infected with ringworm. In one study of dogs who had active skin problems, less than 3 percent had ringworm.
Symptoms of Canine Ringworm
The classic appearance of ringworm on dogs is a spreading circle of hair loss. At the center of the circle, there is scaly skin, and at the periphery there is a red ring (thus the name “ringworm”).
Common areas affected include the face, ears, legs, feet, and tail.
Ringworm can also affect the nails, making them dry, brittle, cracked, and deformed.
In some cases, we can find atypical symptoms with irregular areas of hair loss (not in a circle) spreading across the face or nose, with scaling and crusting.
Ringworm can also result in secondary bacterial infection causing skin redness and itchiness.
Ringworm or Mange?
Ringworm symptoms can easily be mistaken as other skin problems such as demodectic mange. That’s why a proper diagnosis is essential.
Diagnosis and Treatment of Canine Ringworm
Ringworm in dogs can be diagnosed using several methods.
One method is the use of an ultraviolet light (called a Wood’s light).
A few species of the ringworm fungus (e.g. Microsporum canis) will glow a fluorescent color when exposed to the light. Since not all species can be detected by the light, this method is not accurate and the light should be used only as a screening tool.
The most reliable method is by fungal culture.
Hairs, scales and crust from the affected skin areas are collected and placed on a special medium to grow out any fungus that is present, and the ringworm fungus can be identified this way. It takes about 2 weeks for results to become available.
Mild cases of ringworm usually heal by themselves in three to four months.
To speed up recovery in dogs with only one or two isolated lesions, a topical anti-fungal medication such as a 2% miconazole cream, or 1% chlorhexidine ointment will be prescribed.
For dogs with long hair, the hair around the affected areas may need to be clipped off for easy penetration of the medication.
When several areas are involved, in addition to topical antifungal medication, an antifungal shampoo containing miconazole will also be recommended.
In even more difficult cases, oral anti-fungal medications (e.g. griseofulvin, ketoconazole, itraconazole) may be prescribed. However, these medications all have possible serious side effects and should only be used under close veterinary supervision.
Griseofulvin should not be given to dogs who are pregnant.
Prevention of Canine Ringworm
As mentioned above, ringworm spores can survive up to 18 months in the environment. It is therefore essential to eliminate the spores by:
- Sterilizing all the grooming tools
- Vacuuming and cleaning the carpets and upholstery
- Mopping and washing the floors and countertops with diluted bleach
- Discarding the infected dog’s bedding