Dermatophytosis (Microsporum canis, M. gypseum, Trichophyton mentagrophytes) is a cutaneous (skin) infection with one of several keratinophilic species of fungi. Transmission is by direct contact or contact with infected hairs and scale in the environment. Infected hairs in the environment may remain contagious for months to years. Zoonosis (contagion to human) is a frequent problem and is most often associated with the Persian breed and other long-haired cats which can be asymptomatic carriers.

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Diagnosing Ringworm in Cats

Treatment of RIngworm

Treatment should be aimed at eliminating the infection from the host and cleaning the environment. Optimally, affected animals should be separated from other pets in the household. Every confirmed case of dermatophytosis should be treated topically. Total body clipping may be beneficial to decrease environmental contamination by infected hairs and to allow for topical application of medications. The efficacy of antiseptic baths and topical rinses against the fungus vary but each is effective in removing scale, crust, exudates (discharge), and loose, infected hairs. Systemic therapy is often needed to hasten recovery. Medications most often used include:  ketoconazole, itraconazole, terbinafine, and griseofulvin. Griseofulvin can cause serious side effects (leukopenia / low white blood cell count) in the cat. Fungal vaccines have shown little efficacy in controlling dermatophytosis. Animals receiving this vaccine may demonstrate improvement in clinical signs but can still culture positive, thus posing a zoonotic threat.

Environmental decontamination is an important feature in these cases. Re-exposure and re-contamination are a 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) for 10 minutes. This should be repeated a minimum of 3 times. 
  • All surfaces in the environment should be vacuumed, scrubbed, rinsed, and wiped down with a 1:30 dilution of Chlorox.

  • Vacuum bags should be burned or saturated with Chlorox.

  • 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, Nolvasan). 

  • Rugs that cannot be destroyed or removed should be washed with an antifungal disinfectant. Steam cleaning fails to maintain water temperatures of above 43 degrees Celsius 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 clean-up is mandatory if the owner wishes to effectively remove fungi from the premises.


Contributed by:  Karen Helton-Rhodes, DVM, Diplomate ACVD