Thursday, March 14, 2013

Ringworm is not a worm, by Dr. Dana

Ringworm is not a worm.

Well, then, what is it?

Ringworm is the common name for a skin infection caused by a group of fungi; it is not caused by a worm at all. The fungi feed on skin cells and/or hair. In people it causes round, red lesions with a ring of scale around the edges and normal healing skin in the center. Due to the itchy nature and appearance, people once believed it was a worm living in the skin. The fungi responsible are called dermatophytes, “dermato” meaning skin and “phytes” meaning plants. The correct term for ringworm is really dermatophytosis. In animals, ringworm frequently looks like a dry, grey, scaly patch but can also mimic any other skin lesion and have any appearance, and it is usually not itchy.

How did my pet (or my kids) get ringworm?

The spores of dermatophyte fungi are extremely hardy and they can live for years. There are several species of dermatophyte fungi. Different species of fungi come from different kinds of animals or from soil. The fungus can only invade skin that is irritated or abraded; it cannot infect healthy intact skin. This means that freshly shaved, scraped, or scratched skin is especially vulnerable. So, kids with scraped knees, and grownups gardening without gloves, or anyone with dry skin are all very attractive to the fungi.

Infected animals (including people) shed spores into the environment as infected hairs break off and skin flakes off. Some animals are carriers, which means their skin is infected but shows no visible lesions and they can infect others. Ringworm patients undergoing treatment commonly fit in this category towards the end of their care; the skin is still dropping spores but the visible signs of infection have cleared up.

Some people are at greater risk of becoming more seriously infected than others. The fungus takes advantage of people with reduced immune function. This puts young animals and children, elderly people and pets, people who are immune compromised: HIV+, on chemotherapy, steroids like prednisone, or organ anti-rejection medication, as well as highly stressed or significantly ill people and animals are at higher risk.

If you do not already have ringworm at the time your pet is diagnosed, you probably will not get it. Some people become immune to the different strains of ringworm once infected.

How do you diagnose ringworm?

Ringworm lesions on animal skin are rarely the classic ring-shape as in people. Pets are usually not itchy like people either. Some testing is necessary to determine if it is ringworm.

Wood's Light Fluorescence: Microsporum canis, the most common ringworm fungus, will fluoresce (glow) apple green in approximately 50% of cases. Fluorescence is easy to perform and may provide a strong clue that there are dermatophytes on the skin. Further testing is usually indicated to confirm diagnosis especially if it is not fluorescing.

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. Spores are difficult to see, so many veterinarians skip this step.

Fungal Culture: With this test, some hairs and skin scales are placed on a culture medium to try and grow one of the ringworm fungi. The advantage of this test is that it can confirm ringworm but and it tells us which species of fungus is there. Knowing the identity of the fungus may help determine the source of infection. The disadvantag is that fungi require at least 10 days to grow out.

Also, this is the only test that is helpful in determining if animal is a 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. When there is a pet with ringworm in the home, all other pets should be tested.

Biopsy: Sometimes the lesions on the skin are so uncharacteristic that a skin biopsy is done 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 and how your pet appears, or if there are multiple pets or people affected, your veterinarian may begin ringworm treatment right away before the culture or biopsy results are completed.

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. Ideally all pets should be cultured. Limiting access of the pet(s) to one area of the home makes it easier to reduce the area needing repeated disinfection.

Infected pets often require oral medication, which should be supplemented with topical treatment to prevent further environmental contamination. Localized lesions might get away with topical treatment only.

There are several medications being used to treat ringworm. The medications can be expensive, and have significant potential to cause birth defects in pregnant pets. Pregnant owners should speak with their doctor regarding their pet. Treatment with medication typically is continued for 6 to 8 weeks 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.

Griseofulvin 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 damage. Cats infected with FIV (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 less expensive than itraconazole and is often used in multipet situations.

Itraconazole is highly effective in the treatment of ringworm but is available in capsules that are too strong for our smaller pets. This means that a compounding pharmacy must make it into a more useful size. Nausea is a side effect for this medication and it is more expensive than griseofulvin.

Terbinafine and Fluconazole are both less expensive than the above medications and less likely to have side effects so more veterinarians are starting to use these drugs.

Topical treatment for ringworm and disinfecting the environment:

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. Killing the fungus on the pet means topical therapy. Lime Sulfur Dips are recommended usually twice a week and can be performed either by the hospital or sometimes the veterinarian let’s you do it at home. If you attempt this kind of dipping at home, you should expect:
  • Lime sulfur will stain clothing and jewelry, and metal bathroom fixtures 
  • Lime sulfur will cause temporary yellowing of fur 
  • Lime sulfur smells strongly of rotten eggs The dip is mixed according to the label instructions and is not rinsed off at the end of the bath. The pet should be towel dried.
Miconazole (a topical antifungal) and chlorhexidine (a disinfectant) work together when combating ringworm. They are available as a combination rinse as well as shampoo. The rinse, which is allowed to dry on the pet, is effective in killing ringworm spores though lime sulfur seemed associated with faster cure.

The problem with decontaminating the environment is that few products are effective. Bleach diluted 1:10 with water will kill 80% of fungal spores with one application and any surface that can be bleached should be bleached, with the solution remaining on the cleaned surface for 10 minutes. Vigorous vacuuming and steam cleaning of carpets will help remove spores. Vacuum bags should be discarded. To reduce environmental contamination, infected pets should be confined to one room until they have cultured negative. Most of the time, we perform two cultures during treatment, more if either comes back positive. The rest of the house can be disinfected during this confinement period. The hairs and skin particles from the infected individual literally forms the dust and dirt around the house and are the basis for reinfection. Affected animals should be confined to one room which should be cleaned twice a week. It is recommended to clean all areas thoroughly at least 3 times.

Can ringworm go away by itself?

There have been several studies that showed this fungal infection can eventually resolve on its own. Typically, this takes 4 months, a long time in a home environment for contamination to be occurring continuously. I recommend treatment for this infection rather than waiting for it to go away.

What to change if the ringworm infection doesn’t go away:

After a couple of months of medication and dipping, the outbreak is generally over. If the pet is still culturing positive, then it is time to look for where you may have cut corners (not giving oral medication consistently, not dipping, not treating environment thoroughly, not treating carrier pets), if you use generic itraconazole it might not work, your pet may not be responding to the medication you are using so consider changing the oral medication, or consider that perhaps the pet has a defective immune system. This disease can be tricky to eradicate so work closely with your veterinarian. If you become infected, contact your doctor to receive treatment. Veterinarians are not able to make recommendations for human disease or infection, even if the infection came from your pet.

Written by Dr. Dana

Read more or contact Dr. Dana:
Dana Lewis, DVM
Lap of Love Veterinary Hospice
Raleigh, North Carolina  |

Dr. Dana assists families with Pet Hospice and Euthanasia in the Raleigh North Carolina area (Raleigh, Durham, Chapel Hill and the greater Triangle, as well as Wake, Durham, Orange, and Chatham counties. Special arrangements can be made for other surrounding counties and for the Triad area.

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