Ringworm: Not a Worm; Rarely a Ring
By Dr. Kim Everson, DVM
Ringworm is one of my least favorite parasitic diseases. It is a common (especially amongst farm cats and dogs), 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 missing hair sometimes with crusty, scaling skin underneath. On people, the fungus usually creates a reddish ring-shaped rash on the skin (hence the name). It may or may not be itchy. Prognosis for a cure is very good in otherwise healthy animals provided appropriate treatment.
There are several reasons why I hate ringworm.
- 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.
- 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 adoptability 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.
- There is no single 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. 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.
- There is no single 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.
- 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, dusting and laundering is necessary to halt ringworm’s spread. A bleach solution can be applied to bleach-safe surfaces. Many barns have generations’ old ringworm colonies present in the timbers and farmyard soils. It is pretty near impossible to sanitize such a setting.
Most of us who spend time around animals–in our home, 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 pet animals (especially indoor pets), my recommendation is, be aggressive and be vigilant because this particular parasite really bites.
Originally printed in farm news column, Fond du Lac Reporter, June 21, 2015