Dermatophytosis, commonly known as ringworm, is a fungal infection that affects the skin, hair, and nails of pets. Effective treatment involves a multi-faceted approach combining systemic and topical medications, along with diligent environmental cleaning to prevent reinfection and spread. This guide outlines the recommended treatment protocols for both cats and dogs, emphasizing the importance of mycological cure alongside clinical recovery.
Systemic Antifungal Therapy
Systemic antifungal drugs are crucial for shortening the duration of the infection and minimizing the risk of contagion to other animals and humans. Infected pets should be isolated from other animals until clinical cure is evident. However, it is vital to ensure that young animals are not kept in isolation for extended periods, as this can lead to lifelong behavioral problems.
Treatment for Cats
For cats, itraconazole is a well-tolerated systemic option, typically administered at a dose of 5 mg/kg body weight orally every 24 hours on a “week on/week off” schedule. Most cats respond well to this treatment over three to four cycles. Research indicates that itraconazole is generally safe for felines and is not commonly associated with liver toxicity or vasculitis. It is essential to use a commercial veterinary liquid formulation of itraconazole, as compounded versions can have poor bioavailability.
Treatment for Dogs
Small dogs can be effectively treated with itraconazole at the same dosage as cats (5 mg/kg orally every 24 hours). While pulse therapy may also be effective in dogs, this approach has not been extensively documented. For larger dogs, ketoconazole (5 mg/kg orally every 24 hours) or terbinafine (30–40 mg/kg orally every 24 hours) may be more cost-effective options. Treatment for dogs should continue until a mycological cure is achieved, confirmed by negative fungal culture or PCR assay results, which typically takes at least 4 to 6 weeks.
Important Considerations for Systemic Therapy
Certain antifungal drugs are not recommended for specific species or are less effective overall. Ketoconazole should not be used in cats due to its tendency to cause anorexia. Fluconazole is considered the least effective antifungal for dermatophytes and should be avoided. Griseofulvin is no longer recommended as newer drugs like itraconazole and terbinafine offer superior efficacy with a lower risk of adverse effects. Lufenuron is ineffective for treating dermatophytosis.
Topical Therapy for Disinfection
In addition to systemic treatment, topical therapy is essential for disinfecting the hair coat and minimizing the spread of infective spores. These spores are the primary source of contagion and environmental contamination.
Whole-Body Rinses
A twice-weekly whole-body rinse with lime sulfur (1:16 dilution) or enilconazole (1:100 dilution) is highly effective due to their residual activity. In regions where these products are unavailable, a shampoo containing 2% chlorhexidine and 2% miconazole can be used two to three times a week. However, these shampoos lack residual activity. Topical therapy should be continued until a mycological cure is demonstrated, even after systemic treatment has been discontinued.
Focal Topical Therapy
For lesions in difficult-to-treat areas such as the face and ears, adjunct focal topical therapy can be beneficial. A 1-2% over-the-counter vaginal miconazole cream can be safely applied to the face. For ear infections, otic products containing clotrimazole or combinations of miconazole/chlorhexidine or ketoconazole/chlorhexidine are available.
Environmental Cleaning and Disinfection
Environmental cleaning plays a critical role in removing infective material and preventing reinfection. Fungal spores do not multiply in the environment but are easily removed through mechanical cleaning.
Cleaning Procedures
The most crucial step in environmental cleaning is the mechanical removal of organic material and hair using a vacuum or wipes, followed by washing surfaces with detergent until they are visibly clear. After cleaning, a disinfectant effective against Trichophyton should be used to kill any remaining spores. Disinfectant application alone is insufficient; thorough cleaning is paramount. Weekly or bi-weekly cleaning sessions are generally adequate, with ongoing removal of organic material between cleanings. Continue this cleaning regimen until mycological cure is achieved.
Disinfection of Soft Surfaces
Soft surfaces such as bedding and towels can be disinfected by washing them thoroughly in a washing machine; bleach is not necessary. Carpets can be effectively cleaned through shampooing or steam cleaning.
End of Treatment
The successful end of treatment is marked by both clinical and mycological cure. Clinical cure is defined by the resolution of all lesions and the absence of new ones. A Wood’s lamp examination can aid in detecting residual infected hairs in cats infected with M. canis. Mycological cure is confirmed through a negative fungal culture or PCR assay. One negative PCR result is generally sufficient to support mycological cure. Similarly, unless the animal has underlying systemic illness, one negative fungal culture result also indicates mycological cure.
