Ringworm - not a worm at all, actually

Ringworm is the traditional name for an infection caused by a group of fungi. These fungi are called dermatophytes (plants that live on the skin).

Pets get infected with ringworm by having direct contact with dermatophyte spores, which are spread in the environment by spore-covered hairs that have fallen off of infected animals. Infection occurs when a spore comes in contact with the skin. However, the skin must be abraded (scraped, scratched or freshly shaved), as healthy, intact skin cannot become infected.

In animals, ringworm often presents as a grey, dry, scaly patch of skin. An infected animal does not have to show clinical signs of the disease.

Veterinarians usually deal with three species of fungi: Microsporum canis, Microsporum gypseum and Trichophyton mentagrophytes. These come from different environments, and identifying the type of fungi will help determine the source of the infection.

Humans also can get this infection, which is where the name “ringworm” comes from. In humans, the infection appears as a ring of irritated, itchy skin that looks like a worm. Some people are more at risk than others; children, those with compromised immune systems and seniors are most susceptible. If you present no clinical symptoms by the time your pet is diagnosed with ringworm, the risk of you developing the disease is minimal.

Determining a Diagnosis

Your veterinarian has a few methods to diagnose ringworm. 

  • Wood's Light - If a pet is infected with Microsporum canis, it will fluoresce in around 50 percent of the cases. There are some false positive cases as certain medications and seborrhea will glow, as well.
  • Examination under a microscope - This is a good test, but the spores are difficult to see. For that reason, this option isn't commonly used in daily practice.
  • Fungal culture - This is the most common test used in daily practice, and it is quite accurate. The only downside is that it might take up to three weeks for the fungi to grow, which delays diagnosis.

Treatment is usually carried out in a systematic and topical way at the same time, to increase the chances of success. Environmental decontamination is also important to reduce or avoid the risk of re-infection.

Oral Medications

Oral medications used in the treatment of ringworm include:

  • Griseofulvin - Some breeds and life stages are more sensitive to the drug's side effects
  • Itraconazole - This medication can cure the disease two weeks aster than Griseofulvin
  • Terbinafine - Effective with few side effects

Topical Therapy

Topical remedies used in the treatment of ringworm include:

  • A Lime Sulfur bath - The bath is given once or twice a week and can be done at the hospital or at home. The fumes are very strong, with an odor of rotten eggs. Treatment has to be carried out in a well-ventilated area. The dip is to be mixed according to manufacturer instructions. The patient is not to be rinsed at the end of the bath.
  • Pure Oxygen - This is a new type of treatment that is given twice a week. As with Lime Sulfur, the patient is left to air dry. This product does not smell or stain jewelry or clothing like Lime Sulfur will, but in some cases it might not be as effective.

Environmental Treatment

It is critical to keep the cat's environment as clean as possible to prevent re-infection and reduce the risk of infecting other pets in your home. Ringworm is highly contagious.

  • Affected cats should be confined to a room that is easy to clean until two cultures come back negative. The room should be cleaned twice a week.
  • Carpeted areas should be vacuumed for at least ten minutes. The bags should be discarded each time. Hard surfaces should be cleaned with a Swiffer or other electrostatic device.
  • Bleachable areas should be treated with a 1:10 solution. The surface should remain wet for at least ten minutes to kill the spores. Bleach will not kill the spores if they're hidden under dirt, and surfaces must be well cleaned before using bleach. 


There is currently no preventative vaccine against ringworm disease.