Ringworm is the common name given to a fungal infection also known as dermatophytosis. Ringworm is not uncommon in dogs and if your dog has skin problems it may have ringworm. The disease is highly contagious and can be passed on to humans so if any signs develop it is important that you seek veterinary advice immediately.
Ringworm is caused not by a worm but is a fungal disease resulting from infection with Microsporum canis. It is one of the most common zoonotic diseases in pets, i.e. an infectious disease that can be transmitted from dogs to other animals, including humans. Skin lesions, especially on the face, ears and limbs, and nail bed infection are common signs. The appearance is variable and the signs can look very similar to many other canine skin diseases. Patchy hair loss can also be present.
Ringworm is spread through contact with spores. These are carried on hairs from infected pets and can survive in the environment for months or even years. Many dogs that come into contact with the fungus will not show any clinical signs. These animals can however carry the spores and pass these to other pets in their household.
Young dogs, less than 1 year of age, are most commonly infected; but older and sick animals are also at risk. Some breeds, particularly small terriers, appear to have more chance of being infected.
Typically the disease affects the face and front paws. If infected, your dog may have patches of hair loss and red, crusted areas on its face or paws. Scratching and chewing at hair may result in vomiting of hairballs or constipation. Sometimes nails are affected resulting in nail loss or thickening. More rarely sore or ulcerated areas of skin are present.
If your vet suspects that your dog is infected they will want to take hair plucks and samples of coat brushings to confirm the diagnosis. Your vet may use an ultraviolet lamp (Wood’s lamp) to examine your pet’s hair – under ultraviolet light some types of ringworm appear to glow apple green. This is not a definite diagnosis but will identify hairs that can be used for further examination.
A rapid test is to examine the hairs under the microscope to identify fungal spores. It may be necessary to try to grow ringworm from samples and, because the fungus grows slowly, this can take several weeks for a confirmation of diagnosis. To avoid delay treatment may be started while waiting for results of tests.
Although signs of ringworm will resolve in most healthy adult dogs within a few weeks without treatment, treatment is usually recommended because of the risk to other pets and to people. Ringworm can be treated with antifungal agents such as griseofulvin, ketoconazole or itraconazole as prescribed by your vet.
Clipping your pet (using scissors reduces skin trauma) may reduce the risk of your pet spreading the disease. Your vet may recommend application of an enilconazole or chlorhexidine dip or a shampoo twice weekly for 6-10 weeks or until coat brushings are negative for culture.
Gloves and protective clothing should be worn to prevent the spread of infection when treating your dog.
If one pet in a household is diagnosed with ringworm then all other animals (including humans) need to be examined for signs of infection. It may be necessary to treat all in-contact dogs and cats by the administration of oral medication and by applying a topical medication directly to the hair and skin.
Treatment should continue for 2 weeks after the lesions have disappeared or until two samples taken a week apart are negative on fungal cultures.
Infected animals should be isolated and confined to one room to reduce the contamination in other parts of the house. Avoid grooming infected animals until treatment has finished. Contamination by hair and scale can be reduced by vacuuming contaminated rooms and pet bedding. Vacuum bags should be disposed of by burning.
Floors, worktops, litter trays, bowls and cages should be disinfected at least twice a week with 1:10 dilution of household bleach and allowed to dry before giving pets access again. Disposable cloths should be used for cleaning and all grooming equipment should be disinfected.
In people ringworm usually starts as reddish, scaly patch of skin. The areas may be itchy or dry and eventually, it may begin to resemble a ring or a series of rings. The skin lesions may be raised with bumpy borders around a scaly centre. If lesions develop in haired areas of skin then hair loss occurs, usually in a circular pattern. If you develop any skin lesions then you should see a doctor as human lesions will need to be treated appropriately.