WHAT KIND OF INFECTION IS IT?
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| Ringworm lesion |
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| Generalized ringworm lesions |
"Ringworm"
is the common name for the skin infection caused by certain types of fungi. Despite the name, ringworm is not caused by a worm at all. The fungi feed upon the dead cells of skin, nail beds
and hair. In people, this causes a classic round, red lesion with a ring of scale
around the edges and normal recovering skin in the center. Because the ring of
irritated, itchy skin looked like a worm, the infection was erroneously named.
The fungi responsible are called "dermatophytes," meaning "plants
that live on the skin" thus the more correct term for ringworm is
"dermatophytosis." The characteristic "ring" appearance is
primarily a human phenomenon. In animals, ringworm frequently looks like a dry,
gray, scaly patch but can also mimic any other skin lesion and have any
appearance. The fungi live in the hair follicles and cause the hairs to break
off at the surface of the skin. As the fungus multiplies, small round lesions
can become large, irregularly shaped patches of hair loss and spread across the
whole body. Most commonly, ringworm is seen in kittens, likely due to their weaker immune system. Ringworm most commonly affects the face, head and ears. Less commonly, the feet, tail and nails are affected, and even less commonly do we see generalized infections covering the entire body. High humidity and large populations of cats tend to increase the risk of ringworm infection, and certain breeds like Himalayans and Persians are at higher risk, as well. You can read about Samson and his battle with ringworm on one of our other blog posts. This may be due to increased difficulty in grooming all the way down to the skin due to large amounts of long thick fur. FIV positive or otherwise immunocompromised cats are also at higher risk. Regular or frequent bathing of cats may remove protective skin secretions that help protect the skin from fungal infection.
WHERE WOULD MY PET PICK UP THIS INFECTION?
There are about 40 different species of dermatophyte fungi. The most common species to infect humans is the Tinea family of fungi. Cats tend to become infected by Microsporum canis, Microsporum gypseum, and Trichophyton spp. Microsporum canis is responsible for up to 98% of dermatophyte infections and is considered "true" ringworm.
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Different types of dermatophytes look different on culture medium
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The
spores of dermatophyte fungi are extremely hardy in the environment; they can
live for years. All it takes is skin contact with a spore to cause infection.
Infected animals are continuously dropping hairs covered with thousands to millions of spores, because infected
hairs become fragile and easily break off and shed into the environment. Some animals (about 20%) are carriers and
never show signs of skin irritation themselves, but can infect others readily. Ringworm can be transmitted between people, dogs and cats by
direct contact, as well as being picked up from the environment. Environmental
“hot spots” for contracting ringworm are schools or daycares, gyms, and the
out-of-doors in general. Spores may live in bedding or carpet for 18 months or more. Different species of fungi come from
different kinds of animals or even from soil, so determining the dermatophyte
species can help determine the source of the fungal infection.
CAN I GET THIS INFECTION?
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| Ringworm lesion in a human |
Yes,
ringworm is contagious to people; however, some people are at greater risk than
others. The fungus takes advantage of skin belonging to those with reduced
immune capacity. This puts young animals and children, elderly people and pets,
those who are HIV+, people receiving chemotherapy or taking medication after blood
transfusion or organ transplant and highly stressed people and animals at high
risk. If you have cuts or abrasions to the skin, that allows the fungal spores a better foothold, as normal, unbroken and healthy skin is resistant to fungal infection. In general, if you do not already have ringworm at the time your pet is
diagnosed, you probably will not get it, since lesions appear about 10-12 days
after infection. If you find suspicious lesions on your body, check with your
family physician.
HOW DOES THE DOCTOR KNOW THIS IS REALLY RINGWORM?
In
some cases, we know for sure that dermatophyte fungi are present while in other
cases we are only highly suspicious. Lesions on animal skin are rarely the
classic ring-shaped as in people (in fact, in animals, lesions are often not
even itchy) thus some testing is usually necessary. On many animals, ringworm presents as roughly circular areas of broken hairs or bare skin, often with scaly, inflamed skin. Sometimes, ringworm infections can look almost identical to flea allergy dermatitis or other skin diseases. Hair loss is usually involved, but the degree of itchiness and inflammation is highly variable.
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| Hair shaft fluorescence under Wood's Lamp |
WOOD'S
LIGHT
Microsporum canis, the most common
ringworm fungus, will fluoresce apple green in approximately 50% of cases.
Fluorescence is an easy test to perform and may provide a strong clue that
dermatophytes are present. Further testing is usually needed, however, to
absolutely confirm diagnosis. It is important not to mistake scabrous material, dust particles and free-floating skin flakes as fluorescence. If the fluorescence is present, it will light up along the hair shafts at the edge of the lesion.
MICROSCOPIC
EXAMINATION
Your veterinarian may wish to examine
some hairs for microscopic spores. If spores can be seen on damaged hairs then
the diagnosis of ringworm is confirmed; however, as spores are very difficult
to see, many veterinarians skip this step.
FUNGAL
CULTURE
For a fungal culture, some hairs and skin scales are
placed on a special culture medium in an attempt to grow the ringworm
fungi. The advantage of this test is that it not only can confirm ringworm but
also can tell exactly which species of fungus is present. Knowing the identity
of the fungus may help determine the source of infection. The disadvantage,
however, is that fungi require about 10 days to mature to the phase where they can be identified by their special "fruiting bodies" and spores.
Also,
this is the only test that is helpful in determining if animal is an
asymptomatic carrier. The other tests require an apparent skin lesion to test.
A pet with no apparent lesions can be combed over its whole body and the fur
and skin that are removed can be cultured. Carrier animals are usually cats
living with several other cats.
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| Characteristic growth and media color change on fungal culture |
BIOPSY
Sometimes the lesions on the skin are
so uncharacteristic that a skin biopsy is necessary to obtain a diagnosis.
Fungal spores are quite clear in these samples and the diagnosis may be ruled
in or out. Depending on the outcome of preliminary tests, your veterinarian may
begin ringworm treatment right away or postpone it until after more definitive
results are available.
TREATMENT
Commitment
is the key to success especially if you have more than one pet. Infected
animals are constantly shedding spores into the environment (your house) thus
disinfection is just as important as treatment of the affected pet. Areas of
hair loss will likely get bigger before they get smaller. Within 1-2 weeks,
hair loss should stop, there should be no new areas of hair loss, and the crusting
on the skin should subside. If any of these do not occur within 2 weeks, we
should see your pet again. Infected pets generally remain contagious for about
3 weeks after treatment begins.
ORAL MEDICATION FOR INFECTED PETS
There
are two primary medications being used to treat ringworm: Griseofulvin and
Itraconazole (brand name "Sporonox"). Veterinary dermatologists
disagree as to which is better. Both medications are relatively expensive, must
be given with food, and have significant potential to cause birth defects in
pregnant pets.
Treatment
with either medication typically is continued for 1-2 months and should not be
discontinued until the pet cultures negative. Stopping when the pet simply
looks well visually frequently leads to recurrence of the disease.
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| Characteristic Microsporum fungal macroconidia and spores |
GRISEOFULVIN
(brand name Fulvicin)
This medication must be given with a
fatty meal in order for an effective dose to be absorbed by the pet. Persian
cats and young kittens are felt to be sensitive to its side effects which
usually are limited to nausea but can include liver disease and serious white
blood cell changes. Cats infected with the Feline Immunodeficiency Virus
commonly develop life-threatening blood cell changes and should never be
exposed to this medication. Despite the side effects, which can be severe for
some individuals, Griseofulvin is still the traditional medication for the
treatment of ringworm and is usually somewhat less expensive than Itraconazole.
ITRACONAZOLE
This medication is highly effective
in the treatment of ringworm but is available in capsules far too large to be
useful to most small animals. This means that a special compounding pharmacy must
reformulate the medication into a more useful size. Nausea is a potential side
effect for this medication, but otherwise, side-effects are fewer than with Griseofulvin. The primary reason it is sometimes passed by in
favor of griseofulvin is expense. Itraconazole is also effective in treating
many life-threatening fungal infections whereas Griseofulvin only treats
ringworm.
By
increasing the amount of Itraconazole in the environment, we may be creating
resistance in more dangerous fungi which could become a problem over the years.
On the average, cats treated with Itraconazole and nothing else were able to
achieve cure two weeks sooner than cats treated with Griseofulvin.
DOES
PROGRAM CURE RINGWORM?
In the late fall of 2000, the Journal
of the American Veterinary Medical Association published a study of over 200
cases indicating that Lufenuron (the active ingredient of Program) could be an
effective treatment for Ringworm. This began as an observation that animals
using Program or Sentinel for flea control did not get ringworm. Questions
about this work have come up from the public since the release of this work.
The fact is that the study is still under scrutiny by members of the American
College of Veterinary Dermatology and “the jury is still out.” It is clear that
the doses purported to be helpful with Ringworm should not be harmful. At this
time the use of Lufenuron for Ringworm is reasonable if other more conventional
treatments are used at the same time, but its efficacy is controversial and it should not be considered as the only method of treatment.
TOPICAL TREATMENT FOR INFECTED PETS
Both
the above medications work by interfering with fungal reproduction rather than by
directly killing the fungus. This is fine from the pet's perspective as either
medication should be able to clear the fungus without further therapy; however,
we also would like to reduce contamination of the environment. This means
actually killing the fungus on the pet so that the hairs dropped will not be
infectious but applying topical therapy. For many
years cats with ringworm lesions were shaved to allow for easier topical
treatment. We now know that shaving may be spreading the fungus by creating microabrasions on the skin and allowing the spores to take hold in new locations, or simply by spreading spores across the body as the clippers are moved from one area to another. Because of this, shaving
is not always recommended (depending on the number of cats present in the home
and the length and thickness of the hair).
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| Ringworm lesions on an ear |
LIME
SULFUR DIP
Dips are recommended twice a week and
can be performed either by the hospital or at home. If you attempt this kind of
dipping at home, you should expect:
- Lime Sulfur will stain clothing and jewelry
- Lime Sulfur will cause temporary yellowing of
white fur
- Lime Sulfur smells strongly of rotten eggs.
The
dip is mixed according the the label and is not rinsed off at the end of the
bath. The pet should be towel dried. Shampooing is not necessary.
ENVIRONMENTAL TREATMENT
The
problem with decontaminating the environment is that very few products are
effective. Bleach diluted 1:10 will kill 80% of fungal spores with one
application and any surface that can be bleached, should be bleached. Vigorous
vacuuming and steam cleaning of carpets will help remove spores and, of course,
vacuum bags should be discarded. To reduce environmental contamination,
infected cats should be confined to one room until they have cultured negative.
The rest of the house can be disinfected during this confinement period.
THE RINGWORM VACCINE FOR CATS
In
1994, Fort Dodge released a vaccine which could be used either in the
prevention of ringworm infection or in its treatment. Our hospital does not
recommend the use of this product as, while it may prevent the development of
obvious lesions in a cat, it probably will not prevent infection. This means
that vaccinated cats could more easily become carriers of infection. The
vaccine does not appear to be available any longer (since 2003), and was meant to be used in a treatment situation where many cats were
infected. It was designed as a supplement to the treatments described above
rather than as a preventive for cats in general.
WILL RINGWORM GO AWAY BY ITSELF?
There have been several studies which showed that this
fungal infection should eventually resolve on its own. Typically, this takes
four months, a long time in a home environment for contamination to be
occurring continuously. We recommend treatment for this infection rather than
waiting for it to go away.
