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Ring Around the Ringworm

By Kim Everson, DVM

Ringworm is one of my least favorite parasitic diseases. {Having written that prompts me to ask myself what is my most favorite disease! Ear mites are definitely high on the list of creepy, cool parasites that are fun to treat.}

A cat with ringworm lesions on its face (hairloss)

Anyway, I hate ringworm. It is a common, non-lethal contagious fungus (not a worm at all as the name suggests) that infects the skin, hair and nails. There are many different species of ringworm fungi, or dermatophytes, and they can affect just about any species of mammal imaginable: goat, horse, cow, guinea pig, dog, cat, human. Ringworm is fairly ubiquitous in the environment, hanging around in the soil, animal housing structures, and of course on the skin and fur of the animals it calls home.

In animals, a ringworm infection typically appears as patches of hairloss sometimes with crusty, scaling skin underneath. On people, the fungus usually creates a reddish ring-shaped rash on the skin (hence the name). It is variably itchy. Prognosis for a cure is very good with appropriate treatment.

There are several reasons why I hate ringworm.

1. It is zoonotic. This means infected animals can share the fungus with people. In fact, many times pets are presented to me for inspection because a human family member has classic ringworm symptoms and the pet is the suspected source. It stinks when the cute cuddly new kitten is suddenly a pariah.

2. It is sneaky. Like a Typhoid Mary, a ringworm carrier can quietly infect a legion of other animals and never even appear sick. Therefore, even though it is not a deadly disease, it is a population medicine nightmare. In animal shelters, ringworm is an endemic threat to the health and adoptibility of the animals. A ton of money and time is spent testing, treating and retesting shelter animals, especially cats, for ringworm. In some shelters, cats entering the shelter with known or suspected ringworm might even be euthanized to prevent its spread.

3. There is no one great test. A Wood’s lamp can help screen dogs and cats for ringworm because a fair number of cases will fluoresce, or glow. I become quite giddy when a cat or dog ringworm suspect lights up like a city skyline at night under the Wood’s lamp. {It’s almost as cool as watching ear mites swim through mineral oil under microscope magnification.} Definitive diagnosis of ringworm, however, is made by culturing the organism from the fur. This test can take days to weeks and occasionally fails due to the persnickety nature of certain ringworm types who may refuse to grow well in the lab.

Lime dipping a cat with ringworm

4. There is no one great treatment. A diagnosis of ringworm comes with a laundry list of different topical and oral treatment options. Some are antiquated and dangerous. Some are stinky, messy and flat out obnoxious. Others are terribly expensive. Current veterinary protocols for treating ringworm usually involve a combination of multiple obnoxious lime dip baths and costly oral antifungal medication.

5. A ringworm household can turn into veritable Superfund Site. Ringworm is spread through “hairborne” fungal spores, which easily become airborne on shed fur and dust. Careful, thorough vacuuming and dusting (including heating/cooling ducts if the ducts culture positive) and laundering is necessary to prevent re-infection of the affected animal. A bleach solution can be applied to bleach-safe surfaces.

Most of us who spend time around animals–either in our home, in the workplace or on the farm–will have  a ringworm infection at some point in our lives. Fortunately in people the infection is usually fairly easy to treat with topical medications. For affected animals, my recommendation is, be aggressive and be vigilant because this particular parasite really bites.

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