What is ringworm, and what causes it?
Ringworm is a skin disease caused by a fungus. Because the lesions are often
circular, it was once thought to be caused by a worm curling up in the tissue.
However, the condition has nothing to do with a worm.
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.
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?
Diagnosis is made in one of 3 ways:
1. Identification of the typical "ringworm" lesions on the skin
2. Fluorescence of infected hairs under a special light (however, not
all the species of fungi fluoresce)
3. Culture of the hair for the fungus. The last method is the most accurate,
but it may take up to 2-3 weeks for us to obtain a result
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, 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 a dilution of chlorine bleach and water or using some approved disinfectants
that are effective against ringworm spores.
How is it treated?
There are several means of treatment. The specific method(s) chosen for you
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. We have indicated the measures most likely to be effective
in this particular case.
1. Griseofulvin. This is a drug 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 but we will have to check the dog to ensure that the appropriate
progress is being maintained. At that time, your dog should be rechecked to
be sure the infection is adequately treated.
These tablets are not absorbed from the stomach unless there is fat in the
stomach at the time they are given. This can be accomplished by feeding a high
fat diet, such as a rich canned dog food or a small amount of fat trimmings
from meats or by mixing corn oil or other cooking oil in with a small meal or
by allowing the dog to drink some rich cream. This is the most important part
of the treatment.
2. Topical antifungal medication. Apply one of these products to the affected
areas once daily for 10 days. 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 Sulfur 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 odor, tarnishes
jewelry and can be irritant to sensitive skin. It is advisable to wear gloves
if applying this form of treatment.
5. Shaving of the dog's hair. This will remove the infected hair. This, although
a drastic procedure, has to be undertaken when the infection is extensive in
full coated animals.
What should I expect from treatment?
Treatment will not produce immediate results. The areas of hair loss will
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. After at least two
weeks, your dog should be checked again.
How long will my dog be contagious?
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. Minimizing exposure
to other dogs or cats and to your family members is recommended during this
I have heard that some dogs are never cured. Is this true?
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
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