Vet Times The website for the veterinary profession https://www.vettimes.co.uk DERMATOPHYTOSIS IN CATS AND DOGS: SIGNS AND MANAGEMENT Author : Filippo De Bellis Categories : Vets Date : June 20, 2011 Filippo De Bellis examines this skin condition, looking at aetiology and symptoms, as well as providing advice on diagnosis and managing the infection Summary Dermatophytosis is an infection of keratinised tissues (epidermis, hair and claws) caused by three genera of fungi called dermatophytes (Microsporum, Trichophyton and Epidermaphyton). Dermatophytes are transmitted by contact with infected hairs and scales or fungal elements on animals, in the environment or on fomites. The most consistent clinical sign is one or many circular patches of alopecia with variable scaling. However, signs are highly variable, especially in cats. Diagnosis is based on history, clinical signs, ruling out of other diseases and specific tests, including fungal culture. Although the condition may undergo spontaneous remission, treatment should be always performed to prevent the infection spreading. The ideal treatment consists of a combination of clipping, topical therapy, systemic therapy and environmental decontamination. The potential zoonotic aspect of dermatophytosis should always be considered and, in presence of human lesions, owners should be advised to consult their doctor. Key words skin, cats, dogs, alopecia 1 / 7
DERMATOPHYTOSIS is an infection of the keratinised tissues (hairs, nails and/or stratum corneum of the epidermis) caused by fungi of the genera Microsporum, Trichophyton or Epidermophyton. Nearly all feline dermatophytosis is caused by Microsporum canis, with a breed predilection reported for Persian cats; this organism can also cause infection in many other species, including dogs and humans. Trichophyton mentagrophytes and M persicolor, (acquired by contact with infected wild rodents) and various other species isolated from the soil may, on occasion, cause feline ringworm. In the UK, canine dermatophytosis is caused most frequently by M canis and T mentagrophytes. Breed predilections for Yorkshire terriers to acquire M canis infections and for Jack Russell terriers to be susceptible to infection with Trichophyton species (sylvatic dermatophytosis), have been reported. Any age, sex or breed of animal is susceptible to infection. However, generalised dermatophyte infections are usually associated with young age or concurrent debilitating diseases. Transmission Dermatophytosis is a contagious disease and is transmitted by contact with infected hair and scales on animals, in the environment, or on fomites, such as grooming tools, clippers or bedding. Spores, which represent the infectious stage of the dermatophytes, can persist for up to 18 months in the environment. M canis has been cultured from dust, heating vents and furnace filters. The source of M canis infection is normally an infected cat while Trichophyton infections are usually acquired by contact with the reservoir, generally rodents. Other fungi inhabit the rich soil and may be acquired from the environment. Spores attach to the epidermis and germinate to produce hyphae that invade stratum corneum and hair. The period between the beginning of the infection and the onset of the skin lesions is normally seven to 14 days. The disease should be self-limiting and spontaneously resolve in two-and-a-half to three months. There is evidence that feline grooming behaviour can limit the development of lesions. Animals under stressful conditions, young individuals and long-haired cats, or those with compromised immune function, are at greater risk of acquiring dermatophytosis and developing more serious, prolonged and generalised disease. Unapparent carriage of M canis is noted, especially in cats from large catteries and longhaired breeds, such as Persians and Himalayans. Clinical signs 2 / 7
Classically, canine dermatophytosis presents as an expanding circular patch of alopecia with an erythematous and crusted border and a central area of healing ( Figure 1 ), often with the presence of follicular papules and pustules. Facial or nasal folliculitis and furunculosis with alopecia ( Figure 2 ), exfoliation and crusting may be seen in T mentagrophytes and T mentagrophytes var erinacei infections. Lesions affecting the paws or one leg may also be caused by T mentagrophytes ( Figure 3 ). Pruritus is variable. The features of feline dermatophytosis vary considerably. Classically, one or more irregular or circular areas of hair loss with or without scales may be seen ( Figure 4 ). Hairs in these areas often appear broken and frayed. Some cats have severe skin disease while other cats have only very minor lesions or no lesions at all and look completely normal. In long-haired cats, subtle hair loss with minimal other signs are seen more frequently. However, dermatophytosis can look very similar to many other feline skin diseases, including flea allergy dermatitis. In rare cases, cats may appear just to have an infection of the claws. Pruritus can be variable, but, as in dogs, is not common with this condition. Diagnosis Diagnosis of dermatophytosis can be suggested by the history and clinical signs, and confirmed by several methods. There are three tests that can be routinely used for diagnostic purposes. Wood s lamp ( Figure 5 ) is a useful tool by which ultraviolet light is shone on to the hair coat in a dark room and infected hairs may fluoresce with a characteristic apple-green colour. Unfortunately, there is risk of both false negative and false positive results as not all dermatophytes fluoresce, and extraneous substances may cause a similar fluorescence. To decrease the numbers of errors, it is imperative that the hair shafts are seen to fluoresce. For these reasons the results of a Wood s lamp examination is not definitive, but it can provide a very useful method of selecting hairs for further examination, either by fungal culture or microscopic examination. Direct microscopic examination of suspect hairs can provide a rapid positive diagnosis. However, this test is strictly dependent on the experience of the examiner and a negative result does not rule out the disease. Fungal culture of affected hair and scales is the most reliable diagnostic test and is the only way to identify the specific fungus. Hairs for culture are carefully selected (when damaged or associated with skin lesions or when fluorescent at the Wood s lamp examination). Hairs from cats that look normal can be collected by whole body brushing using a sterile toothbrush 3 / 7
or massage brush. The culture may take several weeks to obtain a report and a positive result ( Figure 6 ) indicates that the cat is either infected (clinically or as a carrier) or that there is mechanical hair coat contamination (due to exposure to an infected environment). Demonstration of tissue invasion by the fungal hyphae using histopathology makes a definitive diagnosis, but it is not as sensitive as the fungal culture. Fluorescence microscopy, a method that is not readily available in routine veterinary laboratories, greatly improves the sensitivity of microscopy. Treatment Although in healthy individuals the infection may resolve spontaneously, treatment is necessary in all cases to speed up the resolution because of the risk of infection of humans and contact animals. Optimal therapy of dermatophytosis requires a combination of topical antifungal therapy, concurrent systemic antifungal therapy and environmental decontamination. The treatment should be continued until two consecutive negative cultures (at weekly or bi-weekly intervals) are obtained. Clipping The role of clipping is controversial, as this may cause further dissemination of the arthrospores and creation of new lesions as a consequence of innoculation of spores into skin abrasions produced by clipper blades, but it removes infected hairs (reducing environmental contamination) and aids topical therapy. Clipping should be gentle so as to avoid traumatising the skin. The hair should be disposed of appropriately and all instruments should be disinfected. Topical therapy Topical therapy is important in reducing environmental contamination and works synergistically with the systemic therapy. It is best applied to the whole body by either shampooing or dipping. The only product licensed for the topical treatment of dermatophytosis in cats is a shampoo containing chlorhexidine and miconazole (Malaseb, Dechra). It is to be used twice weekly and it s important to allow a contact time of 10 minutes before rinsing it off. Published studies have suggested that treating cats with M canis using a combination of systemic therapy (based on griseofulvin, no longer used in veterinary medicine) and topical therapy results in a quicker resolution of the skin lesions than with systemic therapy alone. 4 / 7
There are suggestions that this shampoo should be avoided when a cat is treated with itraconazole, as it would remove the drug from the skin and hair and therefore minimise its residual effect. However, there are no published studies to support this assumption. Other products that may be suggested for topical therapy, but are not specifically licensed, include lime sulphur (LimePlus Dip, Dermapet UK) which is used as a dip twice weekly. A study (Newbury et al, 2007) has demonstrated that lime sulphur is efficacious and safe when used synergistically with itraconazole. Enilconazole (Imaverol, Janssen) can be used as a dip twice weekly. It is licensed for use in dogs, horses and cattle, but not in cats. Anecdotal reports have stated possible toxicity, but limited experimental work has failed to reproduce these effects. It is difficult to justify this product in cats instead of miconazole/ chlorhexidine or lime sulphur. Systemic therapy The only product licensed for veterinary use in the UK in cats is itraconazole (Itrafungol, Janssen), available in a liquid formulation. The recommended regime is one week of therapy followed by one week off therapy, repeated for three weeks of treatment. The rationale of this alternate weekly basis regimen is due to the capacity of this drug to be incorporated into the skin and hairs and slowly released, having a residual effect when discontinued. In some cases, a prolonged time between clinical cure and mycological cure (negative fungal culture) may be observed. In such cases, a repeated treatment may be necessary. The product is safe to use in kittens from 10 days of age, but the manufacturer recommends avoiding the product in pregnant or lactating queens. Other available products include terbinafine (Lamisil, Sandoz). This drug is used for various persistent human fungal infections. It is effective, but expensive and needs to be used at a dose of 30mg/kg to 40mg/kg by mouth every 24 hours. Griseofulvin is no longer available as a veterinary formulation for small animal use, the large animal products are unsuitable and, although there are human products available, the licensed product should be used. Griseofulvin can cause side effects in cats, including anorexia, depression, nausea, vomiting and diarrhoea. Griseofulvin is also not recommended for use in kittens less than 12 weeks of age, although there are reports of its use in kittens as young as six weeks. Griseofulvin is teratogenic, and is therefore contraindicated in pregnant animals. As it can cause abnormalities in spermatozoa in experimental conditions in rodents, it is also advisable to avoid using recently treated male cats for breeding. However, there are no studies documenting this effect in cats. None of these medications is licensed for the treatment of canine dermatophytosis in the UK. When treatment is needed, following the cascade, the preferred option of this author is itraconazole. Used at 5mg/ kg once daily and, as in cats, on an alternate weekly basis, it should be continued until two or more negative cultures have been obtained. 5 / 7
See Moriello (2004) in the references for all treatment protocols, including the use of enilconazole, unless another study is cited. Environmental decontamination Decontamination of the environment is an important part of the control of dermatophytosis and consists of two combined approaches: physical decontamination, performed through frequent vacuuming and removal of all potentially contaminated materials that cannot be disinfected, and disinfection, to be conducted using appropriate fungicidal products. In experimental studies, three products have shown 100 per cent fungicidal activity: Household bleach used at the recommended manufacturer starting dilution. Lime sulphur used at the recommended manufacturer starting dilution. Cosmetic drawbacks include a disagreeable odour, temporary yellow staining of light hair coat and staining of clothing and materials. Enilconazole used at the recommended manufacturer starting dilution. This is not licensed for environmental treatment. Prognosis is generally good, but may require long duration of therapy. Catteries and multiplecat households The correct management in these facilities includes separation of carriers from non-carriers, treatment of the infected animals, environmental decontamination and institution of measures to prevent re-infection of the premises. These measures involve discontinuing of the breeding programmes and show campaigns, testing and isolation of new members of the cattery and of cats returning from shows or breeding, and exclusion of visitors. In particular, all cats should receive toothbrush fungal culture and the negative animals should be isolated and re-cultured. The cattery should be isolated and intense treatment on the affected animals started. Pregnant queens should receive topical therapy only (twice weekly) and the systemic treatment started when the kittens are 10 days old. Topical treatment on the kittens can be initiated from four weeks of age, when they should also be cultured for the first time. Kittens should not be sold until at least one or two negative fungal cultures have been obtained. The environmental decontaminating of these facilities requires intense measures, including destroying all bedding, rugs, brushes, and combs. The disinfection should be repeated at least twice weekly; the vacuuming daily. 6 / 7
Powered by TCPDF (www.tcpdf.org) Zoonotic aspects Dermatophytosis is an infectious disease and can be easily spread from animals to people, especially young children. Approximately 50 per cent of people entered in contact with infected animals acquire the infection. The skin signs are variable and most commonly occur on areas of the body in contact with the animals. If any lesions develop, the family doctor should be consulted. References Bond R (2002). Canine dermatophytosis associated with Trichophyton species and Microsporum persicolor, In Practice 24: 388-395. Cerundolo R (2004). Generalized Microsporum canis dermatophytosis in six Yorkshire terrier dogs, Veterinary Dermatology 15: 181-187. Lee Gross T, Irkhe P J, Walder J and Affolter V K (2005). Pustular and nodular diseases without adnexal destruction. In Skin diseases of the dog and cat. Clinical and histopathological diagnosis (2nd edn), Blackwell Science Ltd, Oxford: 16: 406-415 Moriello K A (2004). Treatment of dermatophytosis in dogs and cats: review of published studies, Veterinary Dermatology 15: 99-107. Newbury S, Moriello K, Verbrugge M and Thomas C (2007). Use of lime sulphur and itraconazole to treat shelter cats naturally infected with Microsporum canis in an annex facility: an open field trial, Veterinary Dermatology 18(5): 324-331. Scott D W, Miller W H, Griffin C E (2001). Fungal skin diseases. In Small Animal Dermatology (6th edn), W B Saunders Company, Philadelphia: 5: 336-422. Sparkes A H, Gruffydd-Jones T J, Shaw S E, Wright A I, and Stokes C R (1993). Epidemiological and diagnostic features of canine and feline dermatophytosis in the United Kingdom from 1956 to 1991, Vet Rec 133 (3): 57-61. Sparkes A H, Werrett G, Stokes C R and Gruffydd-Jones T J (1994). Improved sensitivity in the diagnosis of dermatophytosis by fluorescence microscopy with calcafluor white, Vet Rec 134 (12): 307-308. Wright A I (1989). Ringworm in dogs and cats, Journal of Small Animal Practice 30: 242-249. 7 / 7