DERMATOPHYTOSIS
(by Dr Jason Smith 2005)
Ringworm is a skin disease caused by a fungus.
There are several 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.
The incubation period is typically 10-12 days. This means that following exposure to the fungus, about 10-12 days will pass before any lesions occur.
Diagnosis is made in one of 3 ways:
- Identification of the typical "ringworm" lesions on the skin.
- Fluorescence of infected hairs under a special UV light (however, not all the species of fungi fluoresce).
- Culture of the hair for the fungus. The last method is the most accurate, but it may take up to 2-4 weeks for us to obtain a result.
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, it may have been transmitted 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 doctor.
Transmission may also occur from the infected environment, so-called fomite transmission. This is often the method of transmission between animals in a household when the same brushes and combs are used. The fungal spores may be killed using a dilution of chlorine bleach and water.
There are several means of treatment. The specific method(s) chosen for your pet 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 following are the various treatment strategies for ringworm:
1. Tablet systemic medication. These antifungal drugs (e.g. griseofulvin, ketoconazole, miconazole) are concentrated deep in the hair follicles where it can reach the site of active fungal growth. Oral medications should be given daily. Dogs with active lesions should receive the tablets for a minimum of 30 days but we will have to check the pet to ensure that the appropriate progress is being maintained. At that time, your pet should be rechecked to be sure the infection is adequately treated.
The absorption of these antifungal drugs are enhanced if administered with a fatty meal. If you are aware of fat consumption having caused a problem for your dog in the past or if your dog has had an episode of pancreatitis, please let us know immediately.
2. Topical antifungal medication. Apply one of these products to the affected areas once daily until lesions have healed. Do not risk getting it in your dog’s eyes by treating lesions very near the eye.
3. Baths using an antifungal shampoo. A bath should be given 3 times on an every other day schedule. Bathe exposed but unaffected pets once. These baths are important in getting the spores off the hairs so they do not drop into the environment and result in re-exposure. A lather should be formed and left on for 5 minutes before rinsing.
4. Lime Sulphur Dip. This is the traditional treatment for animals affected with ringworm and is effective. It is done twice a week for the first two weeks then once weekly for 4-6 weeks. Other in-contact animals should also receive the treatment at least once. If any develop ringworm lesions, they should also receive griseofulvin. Lime sulphur does have an objectionable odour, tarnishes jewellery and can be irritant to sensitive skin. It is advisable to wear gloves if applying this form of treatment.
5. Shaving of the pet’s hair around the affected areas. This will remove the infected hair. This is invariably undertaken in full coated animals to accelerate the recovery period.
Treatment will not produce immediate results. The areas of hair loss will usually get larger before they begin to get smaller. Within 1-2 weeks, the hair loss should stop, there should be no new areas of hair loss, and the crusty appearance of the skin should subside and the skin look more normal. We will in any case wish to monitor progress. After at least two weeks, your dog should be checked again.
Infected pets remain contagious for about 3 weeks if aggressive treatment is used. Contagion will last longer if only minimal measures are taken or if instructions regarding treatment are not diligently followed. Minimising exposure to other dogs or cats and to your family members is recommended during this period.
When treatment is completed, ringworm should be cured. Although a carrier state can exist, this usually occurs because treatment is not long enough or aggressive enough or because there is some underlying disease compromising the immune system (e.g. Feline AIDS).
