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Ringworm
Introduction
An occasional cause
of skin conditions in pets is caused by Ringworm. The scientific name for
this disease is Dermatophytosis. It is caused by a fungus not a worm, and
the lesion is not always in the shape of a ring. Since fungi are
everywhere in our environment, it is difficult to determine which pets
will develop the problem. The fungus that causes Ringworm can be cultured
from the hair coats of normal dogs and cats. These pets might be carriers
of the disease to other pets, and might even transmit the disease to
people. We tend to see the problem more in young animals and those with compromised
immune systems (for example- FeLV).
People will sometimes
pick up a case of Ringworm from their pet, but just because a pet has
Ringworm does not necessarily mean that the people that interact with that
pet will develop the problem. A dog or cat can transmit Ringworm to a
person without showing any symptoms at all.
Cause
There are 3 specific
fungi of significance in this disease.
- Microsporum canis
The source of this
species of Ringworm is almost always a cat, especially long-haired
cats.
- Microsporum gypseum
This species of
Ringworm is usually from dogs and cats that dig into contaminated
soil.
- Trichophyton
mentagrophytes
This species infects
dogs and cats when they are exposed to rodents or the burrows they
live in.
In cats, almost all cases
of Ringworm are caused by Microsporum canis. In dogs the majority of cases
are caused by Microsporum canis. Which of these 3 main dermatophytes
causes the Ringworm in dogs depends on geographic location.
Symptoms
The skin lesions
that appear with Ringworm are variable, and do not necessarily form a
ring. There will be hair loss, usually in small patches at first.
As time goes on the patches may disappear or appear at other locations on
the skin. There might be scratching due to itchiness. If the hair loss
occurs on the face or feet there is a chance it is due to digging habits
or exposure to rodents.
This patch is typical of the
lesion seen in Ringworm.
A diagnosis of this disease
can not be made based just on the appearance of this lesion. Demodectic
mange, sarcoptic mange, and allergic
dermatitis can look just like this also.
Diagnosis
There are several
different ways to diagnose Ringworm. All require some type of test because
it is impossible to make the diagnosis just by looking at the skin. This
concept holds true for all skin conditions; making a diagnosis of a skin
disease requires all of the aspects of the diagnostic
process.
If a person in a
household has been positively identified with Ringworm by their physician
it is possible they obtained it from their pet, even if their pet has no
symptoms of the disease. This is especially important in multiple cat
households. We will culture these pets using the culture technique we
describe below, but in this case, we might run a new toothbrush over the
hair coat to obtain a sample for culture.
One of the simplest ways
to diagnose Ringworm is with the Woods lamp, which is an ultraviolet lamp,
also know as a black light. 50% of the Microsporum canis species will
fluoresce when the Woods lamp is placed near the area of hair loss. If
there is no fluorescence it is still possible the skin condtion is caused
by a fungus.
The lamp emits a
purple/blue glow from the tube, and when there is fluorescence on the
skin, it has a greenish appearance. Other material on the skin
(dander, medication, etc.) can also fluoresce, so interpretation is
important.
Since only 50% of a certain species of
Ringworm fluoresces under the glow of the Woods lamp, a culture is
used to verify the diagnosis:
The first step in the
culture process is to gently remove hair follicles in the area of
the lesion
These hairs are cultured
in a special media that inhibits bacterial growth and enhances fungal
growth. This culture can be sent to our outside lab or done in house.
Since a fungus is a slow growing organism it can take up to several weeks
to determine if there is growth or not.
The positive
culture on the right, from our in house lab, demonstrates two findings
that are needed for a positive diagnosis. The first is the cottonish
fungal growth, and the second is the reddish color of the culture
media. This color change must occur at the same time the fungal growth
appears.
| The
culture media prior to the start of the test. |
Positive
fungal growth after 10 days of incubation at room temperature. |
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We can even perform a
wet mount and look for fungal spores under the microscope.
Treatment
Topical shampoo therapy
is used in almost every case, especially in longer haired pets. It is
common to clip some or all of the hair in some pets to make it more
effective. These baths will also remove infected hairs that can be the
source of an infection to people or other animals.
Specific anti fungal
cremes are also used when a pet is infected in an area that already has
sparse hair growth, or there are small, discrete lesions. Some of the more
common names of these medications:
- Clotrimazole
- Miconazole
- Chlorhexidene
- Ketoconazole
Oral anti fungal
medications are also used in select cases. They have the potential to
cause side effects, so their use is confined to specific situations.
Program, the oral flea medication, can also be used to treat Ringworm.
In some pets the disease
may resolve by itself after several months. We prefer to treat all pets
though since this will minimize transmission to other pets and people.
"A
four month old kitten had a severe skin condition that was diagnosed as ringworm.
After four months of conventional therapy, the resistant ringworm
infection was not resolved. We put the kitten on Transfer
Factor™ and within 5 days there were no apparent ringworm lesions
remaining. Within a few weeks all the hair had grown back - and the
now 9 month old cat has a beautiful, glossy coat. The ringworm
lesions have not returned."
Sam Jones, DVM
Prevention
Since fungi are
everywhere it is almost impossible to prevent exposure. As is the case in
many diseases, routine hygiene consisting of washing your hands frequently
and keeping your pets hair coat clean will go very far in preventing this
problem. Pets that chase rodents, especially into burrows, might be at an
increased risk. By not allowing your pet's immune
system to become compromised, you can greatly reduce the chances of
contracting ringworm and many illnesses and diseases.
Article
Courtesy of Long Beach
Animal Hospital
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