What is Ringworm?

by Amanda L Maus DVM

Catalina Pet Hospital

Tucson, AZ

Ringworm, despite the name, is actually caused by a fungus that causes a skin and hair infection, especially in areas where the skin is irritated, shaved, or scratched.  Microsporum canis causes most cases, but Microsporum gypseum or Trichophyton mentagrophytes can cause some infections.  The majority of cases occur in kittens but it can be seen in adult cats with stressed immune systems, especially in cat shelters. Cats with Feline Leukemia or FIV are more likely to contract this disease.

Some cases have the characteristic skin lesion of a dry, round hairless area that looks scaly and maybe irritated but not itchy.  Cats are more likely to develop this disease in areas around the face and ears. 

 

Cats with crusty lesions as well as cats with no apparent symptoms (carriers) can drop fungus spores into their home environment.  This can happen even during treatment.

This disease is easily transmitted between cats, and between cats and humans. Ringworm can be spread directly or indirectly through fomites. Fomites are inanimate objects such as blankets, furniture, carpet, pet brushed, cages, or even clothing. This fungus can survive on these objects for months to years.

Unfortunately, this disease is contagious to people, as well as to other pets in the household.  The disease is more likely to cause symptoms in people with a weak immune system.

In pets, the disease is typically diagnosed by use of a Wood’s lamp exam or fungal culture. Treating the disease can be tricky due to the continuous contamination of the environment by the spores.  Isolation of the pet as well as disinfection of the environment is key.  Bleach is a very effective way to kill the spores.  Vacuuming and steam cleaning are very important for that reason.

Although some cats can clear the infection themselves within a few month, this disease is very contagious and the amount of contamination of fungal spores into the environment cause high risk of infection to other pets and humans. There are oral and topical treatments for ringworm.  Both treatments must be performed over 1 to 2 months.  Stopping treatment early can be disappointing since the disease will return again.  A negative fungal culture is necessary to confirm that the pet is free of ringworm.