Ringworm is a skin disease caused by a fungus (plural: fungi). Because the lesions are often circular, it was once thought to be caused by a worm curling up in the tissue. However, there is no truth to that; it has nothing to do with a worm.
There are four fungal species affecting dogs which can cause the disease that we call ringworm. These may also affect humans. The fungi live in hair follicles and cause the hair shafts to break off at the skin line. This usually results in round patches of hair loss. As the fungus multiplies, the lesions may become irregularly shaped and spread over the dog's body.
How long does it take to get it?
The incubation period is 10-12 days. This means that following exposure to the fungus, about 10-12 days will pass before any lesions occur.
How is ringworm diagnosed?
A. Diagnosis is made in one of three ways:
B. Identification of the typical "ringworm" lesions on the skin
C. Fluorescence of infected hairs under a special light (however, only two or the four species of fungi fluoresce)
D. Culture of the hair for the fungus. The last method is the most accurate, but it may take up to 2-3 weeks for the culture to become positive.
How is it transmitted?
Transmission occurs by direct contact between infected and non-infected individuals. It may be passed from dogs to cats and visa versa. It may also be passed from dogs or cats to people and visa versa. If your child has ringworm, he or she may have acquired it from your pet or from another child at school. Adult humans usually are resistant to infection unless there is a break in the skin (a scratch, etc.), but children are quite susceptible. If you or your family members have suspicious skin lesions, check with your family physician.
Transmission may also occur from the infected environment. The fungal spores may live in bedding or carpet for several months. They may be killed with a dilution of chlorine bleach and water (1 pint of chlorine bleach in a gallon of water) (500 ml in 4 liters) where it is feasible to use it.
How is it treated?
There are several means of treatment. The specific method(s) chosen for your dog will depend on the severity of the infection, how many pets are involved, if there are children in the household, and how difficult it will be to disinfect your pets' environment. The one's that are appropriate for your situation are marked.
1. Griseofulvin. This is a tablet that is concentrated deep in the hair follicles where it can reach the site of active fungal growth. Griseofulvin should be given daily. Dogs with active lesions should receive the tablets for a minimum of 30 days. At that time, your dog should be rechecked to be sure the infection is adequately treated.