Moriello KA, Coyner K, et al. Diagnosis and treatment of dermatophytosis in dogs and cats: Clinical consensus guidelines of the World Association for Veterinary Dermatology. Vet Dermatol. 2017; 28:266-e68.
Part II. Treatment and Environmental Control
A variety of treatments are available for feline dermatophytosis. As this family of diseases is transmitted by direct contact with infective material coming from the skin and haircoat of infected animals, treatment and premises control is required to disinfect the haircoat and reduce environmental contamination.
Treatments comprise topical and systemic modalities. Sometimes both methods must be combined to achieve clinical and/or mycological cure. A shelter study has demonstrated that topical therapies can prevent spread of dermatophyte infection to uninfected “in contact” cats. Whole-body topical therapies known to be effective include twice-weekly applications of lime sulfur or enilconazole leave-on rinses, or a miconazole-chlorhexidine shampoo. Enilconazole is available in Canada and Europe, but not in the USA. Either miconazole or chlorhexidine alone, especially chlorhexidine, are not very effective as monotherapies; these agents should be combined for best results.
Other potentially effective topical whole-body therapies include accelerated hydrogen peroxide, climbazole, and terbinafine, but further in vivo studies are required to document the efficacy of these agents. Evidence exists regarding the efficacy of localized or focal treatment of lesions with clotrimazole, miconazole, and enilconazole, but localized treatment of lesions as sole therapy is not recommended due to the wide distribution of dermatophyte spores away from obvious lesions.
No studies specifically addressed clipping of the haircoat as a strategy to reduce shedding of infective material. Whole body clipping may actually spread the infection to other areas of the body, and may cause microtrauma to the skin, additional spread of infective material to the environment, and is stressful to the animal. The two strategies that are most likely to minimize confinement of affected cats and spread of infection to susceptible humans and pets are systemic treatment with oral antifungal therapy and the use of topical therapy twice per week.
Systemic antifungal treatments include itraconazole, terbinafine, griseofulvin, ketoconazole, and fluconazole. Of these, the safest and most effective systemic therapies for cats are non-compounded, brand name itraconazole, and terbinafine. Both of these agents have residual activity in the hair and are effective in recommended treatment protocols. Terbinafine is not licensed for use in small animals, so there are no published target animal safety studies. An itraconazole formulation labeled for cats has recently become available. Griseofulvin and ketoconazole both have significant side effects in cats, and ketoconazole and fluconazole are less effective treatments than either itraconazole or terbinafine.
Lufenuron, originally labeled as a flea preventative because of its ability to disrupt chitin synthesis, has also been recommended in the past as a systemic dermatophyte treatment because chitin also is present in the outer cell wall of fungi. Current evidence shows that lufenuron is not effective in the treatment of dermatophytosis, even in conjunction with other systemic or topical antifungal treatments, and therefore should not be used.
Environmental decontamination and disinfection is often employed to shorten the treatment course of affected animals, as fomite carriage on their hair coat leads to false positive fungal culture or PCR results. Previously, environmental disinfection had been considered to help minimize the risk of dermatophyte transmission to people and other animals, but current evidence indicates that the principal rationale for environmental decontamination is to prevent fomite contamination and false positive fungal culture or PCR results.
The panel found that contact with a dermatophyte-contaminated environment alone, in the absence of concurrent microtrauma to the skin, rarely causes infection in either people or animals. Animal-animal or person-animal contact is the primary mode of dermatophyte transmission. Topical therapy of affected cat(s) and routine cleaning of the environment are the most useful strategies in minimizing environmental contamination.
Confinement of an affected cat or cats to a specific, easily cleaned area of the home or shelter is still recommended as an important part of treatment. Often, unfortunately, confinement of kittens is required at the exact time when they are also in a critical socialization age period, and possibly at the same time when they have just arrived in a foster or permanent home. The cat(s) should be confined, but not isolated from human contact, for the shortest time possible. One study has shown that homes where affected cats were treated with both systemic and topical therapy became culture negative within a week and remained so. Families at home and staff in shelter environments should continue to interact with and handle affected cats and kittens, but they should be informed about risk of fomite transmission and risk of infection.
Socialization and interaction should continue while the cat is confined, but toys, bedding, and other items in the confinement area should be washable and washed daily. People interacting with and socializing the cat should wear gloves as well as shoes and clothing that are washable after each visit. Cats and people can engage in types of play that do not involve direct contact. While dermatophytosis can be cured, missing critical socialization activities during watershed periods may result in lifelong emotional and social maladjustment for the cat. Veterinarians play a key role in counseling owners and shelter staff regarding concerns about feline welfare and quality of life.
Twice weekly cleaning and disinfection of home and shelter environments is recommended. One of the lead authors on the panel recommends to owners, “Clean like company is coming.” Hair should be mechanically removed and areas of concern should be washed and disinfected. Pet hair should be mechanically removed from the area where affected cats are confined. Environmental sampling and testing is not recommended unless there is concern about the potential for false positive fungal cultures and consequent uncertainty about mycological cure in a patient.
Ordinary washing with laundry detergent of washable items is sufficient for disinfection; bleach and hot water have been found to be unnecessary. In general bleach (sodium hypochlorite) is no longer recommended, as it is a respiratory irritant for both people and animals, and can damage many materials. Accelerated hydrogen peroxide or enilconazole (where available) are quite efficacious against dermatophytes and can be used in lieu of bleach on washable surfaces requiring disinfection.
Nonporous surfaces can be disinfected by first mechanically removing all debris and hair, washing of target surfaces with detergent until they are visibly clean, and then application of a disinfectant (an over-the-counter nonphenolic bathroom or general disinfectant is sufficient). Although vacuuming alone does not decontaminate carpets, this is a first step which can be followed by various shampooing or hot water extraction techniques. All surface disinfectants will damage wood floors, but these may be decontaminated by daily use of commercial disposable cleaning cloths designed for dry mopping floors.
The perceived possibility of zoonotic dermatophyte transmission from a contaminated environment is often a source of great anxiety for people. Cat owners and other concerned individuals need to understand that:
–Dermatophytes do not “live” or “multiply” when not on a live host, unlike mildew or environmental molds; they need keratin as a source of nutrients
–Dermatophytes are not like the fungi that cause systemic (“deep”) mycoses; they do not cause respiratory disease or other infections or toxicoses. Unlike molds, dermatophytes are not associated with flooding or natural disasters that produce long-term health risks due to water damage to structures
–Dermatophyte arthroconidia (infective spores) are very easily removed by mechanical cleaning and washing; anything that can be washed can be decontaminated
–Zoonotic disease needs to be taken seriously, but unlike other zoonoses, dermatophyte infections are not life-threatening or life-changing
–Although infected animals can be a source of arthroconidia, people are frequently exposed to ringworm spores, mostly from other people, in many environments: other homes, the gym, schools, swimming pools, the beach, public transportation, theaters, airports, etc.
–Should people with immunocompromised conditions contract dermatophytosis, the disease is still treatable and not fatal. The most common complication in these situations is prolonged treatment. Most often the primary pathogen of concern
is Trichophyton rubrum, a human dermatophyte, not M. canis. [PJS]