Ringworm
in Cats and Dogs
Dermatophytosis
Ringworm (Dermatophytosis) is not a
worm but a fungal disease that
infects skin, hair, and claws by one
of the three types of fungus (dermatophytes)
—
Epidermophyton
,
Microsporum
, and
Trichophyton.
These pathogenic fungi are found
worldwide, and all domestic animals
are susceptible. Cats
are the reservoir for the most
common form of ringworm in pets.
Second in line is carried by rodents
and picked up by curious dogs
digging into rodent burrows. The
third form is a soil fungus.
Ringworm in dogs and cats generally
appears as a red, crusty, rough area
of skin with broken hairs and hair
loss with very little to no
pruritus, or itching, associated
with the infection. Ringworm can,
however, have a wide range of
atypical lesions and appearances.
Due to the susceptibility of young
animals, the disease is more common
in puppies and kittens.
Methods for transmission of ringworm
include:
- Contact with hair and scales from
infected animals
- Contact with contaminated bedding,
grooming equipment, or environment
- Contact with soil containing
fungal organisms
Ringworm is spread by contact with infected animals, and by touching
objects that the infected animal has touched; such as bedding, brushes
or grooming equipment, saddles and other tack, furniture, rugs, etc. Not
every animal or human who touches infected animals or objects will
become infected; the age, immune status, skin condition and grooming
habits of the recipient influence if the fungus is actually able to grow
and infect.
In animals, the classic Ringworm lesions are patchy areas of hair loss
and scaliness, usually with very little inflammation or redness.
Some ringworm in dogs and cats can be contagious to people (zoonotic
disease), especially children. Studies show that in 30 percent to 70
percent of households where the cat has ringworm, at least one person
will get it. People with the highest risk for catching ringworm from
their pet are young children who have never been exposed, the elderly,
or people with a depressed immune system. Once a person has been exposed
to a strain of ringworm, most develop immunity and rarely get the same
strain again. If a person develops ringworm, your pets should be
examined, although many times the source of infection is actually
another person and not a pet.
Infected dogs generally always have a skin lesion at the site of
infection, whereas infected cats can carry the fungus and transmit it
without actually having a skin lesion. In other words, cats can have
the fungus on their coat or transmit the fungus to other animals and
people and not have any noticeable lesions themselves.
Diagnosis of ringworm requires a fungal culture from plucked hair taken
from the edge of a lesion. This can take several days to a few weeks
for growth and a diagnosis. Cats that are suspected of carrying the
fungus but have no lesions can be diagnosed by culturing a sample of the
coat after brushing the cat. An ultraviolet light can be used to
diagnose about 30% of the ringworm infections. Although the disease is
considered to be self limiting in most healthy people and animals,
treatment of infected cats and dogs is usually recommended to speed
recovery and prevent transmission of the fungus. Most animals will
"outgrow" the Ringworm fungus as their body's immune system fights it
off over the course of a few weeks. Animals that are immunocompromised
or very young or old will have a more difficult time. To
some extent, infection may be persistent and widespread in longhaired
breeds of cats.
Clinical signs include:
- Lesions, either single or multiple
- Scaling or crusting
- Patches of hair loss that may be
circular
- Minimal to no itching
- Nodules with ulcers or draining
tracts are rare, but may occur.
Topical treatments
involve clipping the hair, bathing with an antifungal shampoo and following with a rinse
that decrease transmission immediately. Some cases may require systemic
antifungal therapy that has been shown to shorten the course of the
disease. A ringworm vaccine is also available for use in cats in
catteries or multi-cat households where treatment of individual cats is
difficult. The anti-fungal drug of choice in dogs is ketoconazole and in cats is
Itraconazole. Oral medications are generally reserved for severe
and/or chronic infections and can be expensive and with side effects.
Treatment must
continue until the culture results are negative, even though the animal
may look better. Hair re-grows long before the fungus is exterminated.
In a single-cat household, treatment can last 3 to 8 weeks and may be
needed for longer periods in a multi-pet household.
Treatment:
-
Localized infections may be
treated with topical therapy alone.
- Systemic antifungal in combination
with topical therapy should be used
for generalized infections or in
dogs with multiple lesions.
- Thoroughly disinfect and vacuum the
pet's environment.
- All in-contact animals should be
evaluated for possible infection.
Treating your home is also important. Fungal spores can persist in your
carpet for up to 2 years, so re-infection is a concern. The more animals
in the house, the longer the treatment must go on before the environment
is clear. Getting rid of the hair in the house, kennels and pet sleeping
areas are the best way to rid the fungus from the environment. This is
why veterinarians recommend clipping the pet’s hair (alert the groomer).
Fungus likes to grow in dark spaces on hair and debris. If your pet has
ringworm, change the bag each time you vacuum. The parts of a bagless
vacuum can be soaked in diluted bleach water between uses. The only
reliable killer of the ringworm spores is a 1:10 dilution of bleach in
water. Use this with care because it will stain. Sunlight also kills
ringworm. Items that cannot be thrown away can be left in the sun
outside to rid them of ringworm contamination.
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