Ringworm in Cats and Dogs

Ringworm in Cats and Dogs

Animals Affected

Ringworm affects dogs, cats, people, rodents, rabbits, and other mammals.


Ringworm is a fungal infection of the skin.  Contrary to its name, worms are not involved in ringworm infections.  In pets, ringworm primarily is a nuisance.   However, the infection can spread from pets to people.  This makes ringworm infections in household pets a serious concern.

Several different species or types of ringworm exist.  Some are spread in a contagious fashion, by direct contact with infected individuals or by contact with bedding, brushes, furniture, or household objects.  Wild rodents may introduce ringworm into households. Ringworm also occurs naturally in soil, so contact with an infected individual is not needed for a pet (or person) to contract ringworm.  In some instances, people with ringworm may spread the infection to their pets.

Animals that contract ringworm often are young, with immature immune systems. 

Ringworm is a nebulous, fractious, frustrating, and poorly understood syndrome.


Symptoms of ringworm in cats and dogs vary widely.  However, most ringworm lesions appear as small, discrete areas of abnormal skin.   Features of the lesions may include:

  • Hair loss
  • Scabs
  • Red skin
  • Thick skin
  • Scaly skin
  • Crusts or yellow debris adhering to the skin

Ringworm lesions may be itchy and incite scratching in pets. However, this is not always the case.

Risk factors

Generally, animals with damaged skin or immature or compromised immune systems are at increased risk of ringworm.  Specific risk factors include:

  • Youth (less than two years old)
  • Diseases that weaken the immune system, such as feline immunodeficiency virus, feline leukemia virus, or cancer
  • Purebred Yorkshire terriers, Persian cats, and possibly Parson (Jack) Russell Terriers and German Shorthaired Pointers
  • Flea infestation
  • Malnutrition
  • Stress
  • Skin trauma or injury


Some types of ringworm are contagious to people. The infection can be spread among pets in the house, and very hard to eliminate. However, serious illness in pets is rare.


The most effective way to diagnose ringworm is to use a special type of culture medium to grow the fungus from hair of pets.  Because the fungus grows slowly, culturing ringworm can take up to ten days.   Basic skin tests, including examination of hair under ultraviolet light or under a microscope, will detect some (but not all) cases of ringworm.


In many cases, ringworm will not resolve until the animal’s immune system mounts an effective response. Once the animal’s immune system becomes active, some cases of ringworm will resolve spontaneously without treatment over time.

Even with treatment, ringworm can take several weeks or months to resolve.

Topical antifungal medications may help speed recovery.  Oral medications frequently are used as well, although long-term treatment is required and some oral medications may cause severe side effects.   Both types of medicines must be used at least for several weeks to be effective.

Program® (lufeneron), an oral medication originally marketed as a flea preventative, may be effective against ringworm.  Although its use is controversial, it has a very low rate of adverse side effects.

Clipping hair from the affected area of skin is controversial.  Some experts believe that it speeds recovery from ringworm.  Others believe that it slows recovery.  However, most agree that it reduces contamination of the house with ringworm.

Vaccines against ringworm are available, but no consensus exists on whether they are effective.

Oral fatty acid supplements may lead to stronger skin, and therefore decreased incidence of ringworm.  However, the evidence supporting this is not compelling.

No single treatment is accepted as the best one, and none is perfectly effective.   Ringworm is a difficult and frustrating disease to treat.


During the course of treatment, repeated ringworm cultures or skin tests may be needed. These frequently occur at three week intervals, although the timing may vary from case to case.


Ringworm can spread from pets to people. Therefore, if your pet has ringworm and any family members develop skin problems, they should seek medical attention immediately.

Ringworm from pets can contaminate the house in which they live, leading to infection in people and other pets.  Owners of pets should be aware of this and take steps to prevent household contamination.   Practically speaking, preventing this contamination is very difficult.  To give you an idea of how difficult this is, please enjoy the following quote from The 5 Minute Veterinary Consult Clinical Companion: Small Animal Dermatology, Ed. Karen Hellen Rhodes (Lippincott, Williams and Wilkins, 2002) page 647:

“Environmental decontamination is an important feature in these cases.  Re-exposure and re-contamination are a [sic] constant problem.  All contaminated equipment, toys, feed containers, transport cages, scratching posts, grooming supplies, bedding, etc. must be removed from the environment.  Any item that cannot be washed in a bathtub or washing machine should be destroyed.  Salvaged items must be washed in hot water using an antifungal soap (Nolvasan scrub), rinsed, and then soaked in a 1:30 dilution of 0.5% sodium hypochlorite (Chlorox) [sic] for 10 minutes.  This should be repeated a minimum of three times.  All surfaces in the environment should be vacuumed, scrubbed, rinsed, and wiped down with a 1:30 dilution of chlorox [sic].  Vacuum bags should be burned or saturated with chlorox [sic].  Furnace and air conditioner filters will need to be changed and discarded once a week.   Daily spraying of filters with a Nolvasan (2% chlorhexidine) solution at a 1:4 dilution will help decrease the number of fungal spores that are recirculated.   Books, lamps, bric-a-brac, bed linens, and furniture must also be vacuumed and wiped once a week with an antifungal liquid (Chlorox [sic], Nolvasan).  Rugs that cannot be destroyed or removed should be washed with an antifungal disinfectant. Steam cleaning fails to maintain water temperatures of above 43oC at the carpet level and may not be a reliable method to kill fungal spores unless an antifungal disinfectant (Nolvasan) is added to the water. This massive cleanup is mandatory if the owner wishes to remove fungi from the premises.”

There you have it.  If you want to remove ringworm from your house, you must destroy your carpet, burn your vacuum cleaner bags, and wipe down your books, furniture, and bric-a-brac with bleach, among many, many other things.

If your pet has ringworm and you cannot manage to follow the above recommendations (although, especially if I find myself in a court of law, I emphasize that the above recommendations are the official recommendations of drbarchas.com), at the very least remember that your pet has a disease that could spread to you.  Do your best to isolate the infected pet, and try to prevent human and animal exposure to such items as bedding and brushes that are likely to have large amounts of ringworm on them.

Copyright © Eric Barchas, DVM All rights reserved.
The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.