Ringworm

By Nancy Otten, Animal Health Technologist

 What is ringworm and what are the symptoms?

 Ringworm, or dermatomycosis, is an infection of the skin, hair or nails by a fungus.  It’s an important disease because it can be transmitted to humans from animals.  The most typical symptom in humans is a scaly area surrounded by a red ring of inflamed tissue.  It was once thought that this round ring was a worm curled beneath the skin surface thus the misnomer ringworm.  Although this red ring is a typical symptom for people, the symptoms can range from a small, scaly area to a blistered, infected lesion, depending on what species of fungus has infected them.  In dogs and cats, the symptoms can include hair loss, broken hairs, scaly skin, itchiness and sometimes redness at the outside edge of the infected area.  If the nails are infected, they will become roughened and pitted.  Sometimes the animal won’t have outward symptoms of the disease at all (this is more common in cats.)     

 How is ringworm transmitted?

 The most common way for an animal or person to get ringworm is through contact with an infected animal or person.  We can get ringworm from dogs, cats, rodents and cattle and they can get it from us.  Another way people and animals can get ringworm is from handling contaminated soil.  There is a certain species of fungus that prefers to live in the soil but will infect the skin, hair and nails of people and animals.  Another way that we can get ringworm is from coming in contact with spores in the environment.  When an individual is infected, the fungus sheds spores into the environment.  These spores are very resistant and can remain infective for a year.

 Kittens, puppies and children are most susceptible to ringworm because their immune system isn’t developed enough to resist the infection.  Adults can get it too but it usually occurs when there is a break in the skin, or the skin is stressed in some way, facilitating infection.  

 How is ringworm diagnosed?

 If you suspect your dog or cat has ringworm, you will need to make an appointment with a veterinarian.  The vet will need to do a few things to confirm a ringworm diagnosis.  The first thing that they will do is take a skin and hair scraping and look at it under the microscope for evidence of fungal growth.  Next they may expose the infected area to a Wood’s lamp.  A Wood’s lamp emits ultraviolet light and under this light about 50% of ringworm species will fluoresce.  Because only 50% will fluoresce, a negative result doesn’t necessarily mean that the infection isn’t ringworm.  The definitive test for ringworm is to do another scraping and to place these skin cells and shafts of hair on a special growth media.  This media inhibits bacterial growth but encourages fungal growth.  If after 3 weeks no fungal colonies have grown, the animal is negative for ringworm.  If a colony grows and the media simultaneously turns red, the animal is positive for ringworm.  

 How is ringworm treated?

 The newest way to treat ringworm is to double dose Program for 2 months.  Program is a product that is typically used to treat dogs and cats for fleas.  It works on fleas by disrupting the production of chitin.  Chitin is the principal constituent of the hard exoskeleton of fleas.  Chitin is also found in some fungi, including those species that cause ringworm.  Because the fungal spores can live in the environment for a very long time, your home will need to be cleaned thoroughly.  This means that you will need to clean the floors, walls and behind furniture.  You will need to clean your pet’s bedding very well, or throw it out altogether.  Use disinfectants with bleach because bleach is one of the only things that will kill the fungus.  Clean as much as you can with a bleach solution.  For items that bleach would ruin (carpets, upholstered furniture) vacuum them thoroughly and then dispose of the vacuum cleaner bag immediately.