RINGWORM (DERMATOPHYTOSIS)
What is ringworm?
Ringworm is a fungal infection of the superficial layers of the skin, hairs
and nails. The fungi responsible for ringworm belong to a specialized group
known as dermatophytes, and these can cause disease in both man and animals.
Some species of dermatophytes will only infect man, or only infect certain animals,
whereas others can be spread from animals to man.
In cats, one type (species) of dermatophyte called Microsporum canis
is responsible for almost all ringworm infections, and this species in addition
to being infectious to both cats and dogs, will also readily infect man.
What does ringworm look like?
The most common clinical sign associated with ringworm infection is one or
more areas of alopecia (hair loss) which occurs due to the increased fragility
of infected hairs. Most typically, infection will produce a discrete irregular
or circular patch of hair loss, accompanied by variable scaling, crusting, thickening
and reddening of the skin. However, infection may sometimes cause other signs
including generalized disease where a much larger area of the body is affected
often with patchy hair loss.
How can you diagnose ringworm infection?
Diagnosis of ringworm infection is usually straightforward, although the disease
has to be distinguished from a variety of other possible causes of hair loss.
When hairs infected by Microsporum canis are examined under ultraviolet
light (a Wood's lamp), they often emit a yellow-green fluorescence, and this
is a simple and rapid test for the presence of this particular dermatophyte.
However, not all dermatophytes cause fluorescence of infected hairs, and contamination
of the hairs with other substances can also sometimes result in fluorescence.
Confirmation of the diagnosis is therefore important, and is made by microscopic
examination of infected hairs and/or culture (isolation) of the fungus from
hair samples submitted to a laboratory. Results from the latter test may take
up to three weeks.
Treatment of ringworm
Although in many cats, ringworm is a self-limiting infection (with resolution
typically taking 3-5 months), treatment of the disease is always indicated
to minimize the risk of spread of infection to humans (particularly children)
and to others cats (and dogs).
Two forms of treatment can be used for cats with ringworm - topical therapy
(application of creams, ointments or shampoos) and systemic therapy (administration
of anti-fungal drugs by mouth). In addition, attention must also be given to
cleaning the environment.
1. Topical therapy
Occasionally, topical therapy is used alone for treatment of ringworm, but
more commonly it is used in combination with systemic therapy, or systemic therapy
may be used alone. Various creams and ointments are available to apply to localized
areas of the skin affected by ringworm, or if there is more generalized disease
your veterinary surgeon may advise the use of a shampoo. It is extremely important
only to use preparations that have been specifically provided by, or
recommended by your veterinary surgeon for topical treatment of cats.
2. Systemic therapy
For most cases of ringworm, effective treatment will require administration
of an oral anti-fungal drug. The most widely used drug for this purpose is griseofulvin,
although newer alternative drugs are now becoming available. The response of
individual cats to treatment varies, and it is important that therapy is not
stopped too early to avoid recurrence of the disease. In most cases this means
that cats must be treated for a minimum of six weeks, and in some cases much
longer therapy is required. If there is more than one cat in the household,
it is possible either to try and separate infected from non-infected cats and
just treat the infected ones, or in some situations it may be preferable to
treat all of the cats - your veterinary surgeon will be able to advise you regarding
your own circumstances.
3. Environmental cleaning
Hairs infected with ringworm contain numerous microscopic fungal spores which
can be shed into the environment. Infection of other animals and humans can
therefore occur either by direct contact with an infected cat, or through the
environmental contamination with fungal spores. In addition to minimizing direct
contact with an infected cat, it is therefore also important to attempt to keep
the environment free of spores. Topical treatment of affected skin, and clipping
of infected hairs (with careful disposal) may help to reduce environmental contamination,
and it is also worthwhile considering restricting the cat to certain rooms of
the house that are easy to clean. Thorough vacuum cleaning of rooms where the
cat has access to is the best way to minimize environmental contamination, and
this should be done as frequently as is possible (e.g. daily or every other
day). In addition, the use of diluted bleach is recommended in areas that can
be readily disinfected.
Will my cat recover?
The vast majority of cats, if treated appropriately, will recover from ringworm
infection within a few weeks. While the appearance of the lesions may not change
much during the first week or so of treatment, some response (improvement) should
be evident within 2-3 weeks. Occasionally, despite appropriate treatment the
infection persists, and in this situation your veterinary surgeon may have to
try alternative anti-fungal drugs.
The risk to humans
Ringworm can be transmitted quite readily to humans (particularly children)
and it is therefore important to take appropriate steps to minimize exposure
to the fungus while the cat is being treated (see 'Environmental Cleaning').
If any humans in the house develop skin lesions (small patches of skin thickening
and reddening, or patches of hair loss) early medical attention should be sought.
Ringworm in humans generally responds very well to treatment.
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