What Is Ringworm, and How Do Pets Get It?

Ringworm on human arm (Trichophyton mentagrophytes) / Credit: CDC/Dr. Lucille K. Georg
Ringworm on human arm (Trichophyton mentagrophytes). Credit: CDC/Dr. Lucille K. Georg

Ringworm derives its name from the classic red, round "worm-like" lesion seen on human skin that is infected. It is not a worm, though; it is a fungus that is spread from animals to humans.

Dermatophytosis is the medical term for "fungal infection of the skin, hair or claws" (keratinized tissue). Ringworm is not a worm, it is a fungus that can infect the skin of animals and humans. Some species of dermatophyte fungi live in the soil, some are adapted to humans, and some are adapted to animals, with worldwide distribution.

The animal dermatophytes are the ones known as "ringworm." Because it is transmissible to humans from animals, it is also known as a zoonotic disease.

How Ringworm Is Spread

Ringworm is spread by contact with infected animals, and by touching objects that the infected animal has touched; such as bedding, brushes or grooming equipment, saddles and another tack, furniture, rugs, etc.

Not every animal or human who touches infected animals or objects will become infected; the age, immune status, skin condition and grooming habits of the recipient influence if the fungus is actually able to grow and infect. Young, old and those with suppressed immune systems are most at risk.

What Ringworm Looks Like

In animals, the classic ringworm lesions are patchy areas of hair loss and scaliness, usually with very little inflammation or redness. It is not usually itchy.

In humans, the lesions depend on the type of fungus and the location of the body. Most commonly, lesions are red, raised and itchy, sometimes scaly.

How Ringworm Is Diagnosed

Ringworm is best diagnosed by doing a fungal culture -- adding some hair and skin scraping material to a tube of growth media (culture) and seeing what grows on it. This can take several days to a few weeks.

A quick "in office" test is the Wood's lamp test, using an ultraviolet (black) light in a darkened room to see if the affected area will fluoresce to a yellow-green. It should be noted that not all ringworm fungus infections will fluoresce. Dander or other non-ringworm conditions may fluoresce, so interpretation can vary. A fungal culture is needed for definitive diagnosis of ringworm.

Treatment for Ringworm

In some cases, ringworm will resolve on its own. Ringworm treatment varies with the severity of the infection. In mild cases, an anti-fungal shampoo or lime sulfur dip is used. Shaving the affected areas is also helpful.

For more advanced cases, your veterinarian may prescribe oral antifungal medications in addition to the topical treatments. Oral medications are generally reserved for severe and/or chronic infections and can be expensive and with side effects. Please speak to your veterinarian about what treatment is best for your pet's condition, age, and general health status.

Ringworm in the Environment

Ringworm can survive in the environment up to 18 months if the conditions are right. This fungus is also very contagious between animals - humans and pets alike, so environmental decontamination is necessary.

Killing the fungus and ridding it from the environment is difficult. Here are some tips to help.

  • Confine contaminated pets to one room.
  • Vacuum deeply and often, taking care to dispose of vacuum bags or empty canisters.
  • Dispose of rugs and carpets if you can.
  • Wash or dispose of all bedding and toys.
  • Wash applicable surfaces with soap and water and disinfect with a 1:10 diluted bleach solution (1 part bleach, 10 parts water) or veterinary disinfectant such as VirkonĀ® S.
  • Repeat these steps often until the problem is resolved.

For additional environmental ringworm tips, please see the University of Guelph Worms and Germs ringworm site.

Reference: Merck Veterinary Manual, 9th ed.

Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.