Canine Ringworm

Canine Ringworm | Rochester MN

Despite the misleading name, ringworm has nothing to do with worms. Ringworm is a highly contagious fungal infection of the skin and nails. Typical signs of ringworm on cats and dogs are focal areas of crusting hairloss, especially on the face, head, and feet. These lesions may or may not be itchy.

Ringworm is a ZOONOTIC disease, meaning that it CAN BE TRANSMITTED TO PEOPLE. The typical time period (incubation time) from exposure to clinical signs of disease is between 4 days and 4 weeks.

Kittens and puppies less than 1 year old are most prone to infection. Long haired, geriatric, or otherwise immunocompromised cats are also more susceptible. This fungal disease is easily transmitted by contact with dishes, bedding, or toys that have been contaminated. This is why it is so easy for this disease to spread like wildfire in a kennel or shelter environment.


Diagnosis of ringworm disease is based on history of exposure, clinical signs of skin disease, a positive ultraviolet Wood’s lamp test (fungal coated hairs glow a bright apple-green), or positive fungal culture (gold standard). A typical history may involve adopting a new kitten recently from a shelter, since ringworm is common in high population density, high stress environments.


Cats and dogs infected with ringworm may experience a spontaneous remission without treatment, but it can take a very long time (3 months or more) for this to occur. In the meantime, the affected individual can infect countless other animals and people. They can also suffer from uncomfortable infections secondary to the ringworm infection or just the discomfort of the ringworm lesions themselves.

Treatment is recommended because it hastens clinical cure and reduces environmental contamination. Ringworm fungal spores shed easily into the environment and are viable for 18 months. Treatment can be frustrating and expensive (also smelly if a lime sulfur dip is used), so an individual plan must be made for each affected patient.

Lesions should begin to resolve within 1 to 3 weeks after initiating treatment (unless you’re dealing with a resistant strain). However, infected pets remain contagious to other animals and people for at least another 3 weeks after treatment begins. Most treatment regimens last 4-6 weeks, but the only way to confirm that an infection has truly resolved is with a series of 3 negative weekly fungal culture tests.

A treatment plan can be divided into oral medications, topical therapies, and environmental decontamination:

  1. Oral medications:
    • Griseofulvin – always give with a fatty meal to increase absorption
    • Ketoconazole – dogs only
    • Itraconazole – growing in popularity, but expensive, and can be difficult to obtain
    • When using any of the oral medications, be sure to monitor carefully for any adverse reactions. Side effects are rare, but can be quite serious, even life-threatening. Monitor for and report any vomiting, anorexia, diarrhea, or listlessness.
  2. Topical therapies
    • Dips – Lime sulfur dips are often used if the skin lesions are in accessible locations and the family member performing the dip does not have any respiratory compromise. (The dip has a powerfully strong odor which can be overwhelming for some.) This dip can also leave a yellow tinge to the fur. These dips are often repeated twice weekly during the treatment period.
    • Medicated shampoos – Miconazole + Chlorhexidine shampoo may be used if the patient or the family cannot tolerate the lime sulfur dips.
    • Creams – The affected areas can be gently cleaned with betadine and water, patted dry, and then an anti-fungal cream (such as miconazole or clotrimazole) can be sparingly applied every twelve hours. Avoid eye contact with this cleaning and topical regimen, and be sure to wash hands thoroughly after any contact with the infected pet.
    • Clipping – Once universally recommended to treat ringworm patients, the practice of clipping is now restricted to long haired cats that cannot adequately groom themselves and may become horribly matted with dipping.
  3. Environmental decontamination
    • Since fungal spores shed into the environment are viable for 18 months, decontamination is important. If possible, infected pets should be confined to a smaller area of the house to ease cleanup.
    • Ringworm spores are durable and can persist in carriers, furniture, carpet, heating vents, and furnace filters to infect (or reinfect) other cats at a later date.
    • Ringworm can be spread by contamination of human hands and clothing.
    • Bleach whatever can be safely bleached with a 1:10 solution.
    • Vacuum carpets daily for one week. Seal off and dispose of a vacuum bag each day.
    • Electrostatic cleaners (such as a Swiffer) or damp mopping are better than sweeping because they don’t “stir up” spores and debris.
    • Commercial steam cleaning of carpets kills ringworm spores.
    • Replace furnace filters and vacuum heating and cooling vents, but cleaning duct work is usually not necessary.
    • Cover the spots where the cat sleeps with a towel or sheet that can be replaced every few days and laundered with bleach to remove spores. Ringworm laundry should be kept separately from other laundry.
    • Wash the pet’s bedding and toys with a disinfectant that kills ringworm spores.
    • Discard anything that cannot be effectively cleaned (such as a carpeted cat climbing tree)

Please ask us any more questions that you may have concerning ringworm or prevention.

Quarry Hill Park Animal Hospital
2554 Clare Ln NE
Rochester, MN 55906

Phone: 507-285-1059

Hours of Operation
M W F: 7:30 am - 5:00 pm
Tue, Thu: 7:30 am - 5:30 pm
Sat - Sun: Closed

AAHA Certified