

Feline Dermatophytosis: Topical and Systemic Treatment Recommendations
Vet Med 98[10]:877-884 Oct'03 Symposium 37 Refs
Karen A. Moriello, DVM, DACVD
Dept of Medical Sciences, SVM, University of Wisconsin-Madison, Madison, WI
53706
ABSTRACT:
Since dermatophytosis is highly contagious and zoonotic, treatment must be effective,
or the disease will continue to spread. These guidelines will help you formulate
the best therapeutic protocol for each case.
FULL TEXT:
In the first article of this symposium, I reviewed key aspects in the pathogenesis
of feline dermatophytosis. In the second article, I described practical diagnostic
testing. This article presents treatment strategies for single or multiple cats
with dermatophytosis. The key points from the first and second articles to keep
in mind when making treatment decisions with clients are:
Endpoint of therapy
I find it helpful to give clients a perspective on what the desired outcome of treatment is before launching into a discussion on how to get there. Throughout the last decade, I have defined the endpoint of therapy to be a mycological cure; however, I would like to propose that veterinarians consider the endpoint to be both a mycological cure and a decontaminated environment. Both are required to prevent reinfection in cats and exposure of people to this zoonotic disease. It may help clients to grasp therapy concepts if you compare treating this disease to treating fleas: Both diseases are treatable and curable, require treatment of all in-contact animals, require treatment of the host and the environment, and are highly contagious and of zoonotic importance.
Cats will attain a clinical cure before a mycological cure. A mycological cure
is defined as two or three consecutive negative toothbrush fungal culture results
at weekly or biweekly intervals, and treatment should continue until all these
negative culture results are obtained. Two negative results are usually sufficient
in single-cat situations. Three negative results are preferred when multiple
cats are involved.
As for environmental decontamination, infective material can remain viable in
the environment for up to 18 months under optimal conditions of temperature
and humidity. In addition, cats shed infected hairs and spores into the environment
throughout treatment. Contact with infective material will increase the risk
of reexposure, reinfection, and prolonged treatment. Decontaminating the environment
involves aggressive and thorough cleaning and regular disinfectant application.
The more cats involved in an outbreak, the longer the treatment and decontamination
periods will last.
Overview of treatment strategies
A cat that has a positive Microsporum canis culture result requires medical
care, whether it has clinical signs or is simply a mechanical carrier of the
fungus. Treating dermatophytosis, especially in multicat situations, involves
an individually tailored plan that includes some combination of clipping the
coat, topical therapy that the client is able and willing to do, systemic antifungal
therapy that the cat can tolerate and the client can afford, reasonable suggestions
for environmental decontamination, and a case-by-case plan for monitoring for
and preventing reinfection.
Two questions are commonly encountered when antifungal therapy is discussed:
Is it absolutely necessary to treat cats topically (i.e. is systemic therapy
alone effective)? And, can cats be successfully treated with topical therapy
alone (i.e. is topical therapy alone effective)?
The answers to both questions are yes and no, depending on the cat, the severity of infection, finances, and available drugs. The answers also depend on how many cats are involved in the outbreak, whether the cat's coat has been clipped, and how much environmental contamination is involved. After discussing the required endpoint of therapy with clients, I ask the clients two questions before discussing treatment options.
If the answer to either question is yes, I recommend aggressive therapy for
dermatophytosis regardless of the cat's hair length or severity of lesions.
This recommendation includes clipping all the hair on the body and administering
topical and systemic therapy until a mycological cure is attained. If the cat
is part of a multicat household, additional measures need to be taken (Figure
1).
Identifying animals at risk
Any treatment plan will fail if the at risk population is not properly identified. Once a positive culture result is found in a cat, immediate consideration needs to be given to other animals that the cat is living with or has contact with on a daily basis. In this situation, one or more of the following actions are needed:
Figure 1: Guidelines for Treating Dermatophytosis in Cats

Step 1: Determining whether clipping the coat is necessary
Clients often have a much greater emotional attachment to hair than do veterinary dermatologists. I find it ironic that clients fret over the aesthetics of clipping a cat's coat when they are faced with treating a disease that causes, among other signs, hair loss. Clipping the coat is not necessary in every case of feline dermatophytosis, but it is optimal in every case. When dermatophytes invade hairs, they make them fragile and easily fragmented. When hair shafts break, infected hair fragments and spores are shed into the environment and onto the coat. This shedding increases the risk of spreading the disease and increases the probability that the cat may become reexposed to spores in the environment and continue to have positive culture results.
Clipping the coat removes infected hairs and minimizes continued shedding of hair fragments and spores. It also makes topical therapy application easier and allows for more thorough penetration of the topical antifungal agent. In addition, clipping helps shorten the duration of therapy and ultimately decreases the cost of treatment.
However, clipping the coat may require sedating the cat and is time-intensive. It may temporarily worsen the infection by causing microtrauma to the skin. And it may result in environmental contamination if appropriate efforts to capture infected hairs and spores are not taken.
Any cat with dermatophytosis that lives with children, elderly people, or anyone
with immunosuppression must have its coat clipped, because it is important to
eradicate the infection as quickly as possible in these situations. Clipping
the coat is also necessary in shorthaired cats with generalized dermatophytosis
and in all longhaired cats with dermatophytosis, regardless of the severity
of the lesions.
Clip the coat with a No. 10 electric clipper to a length less than 2 cm. In
shorthaired cats with focal lesions, children's metal blunt-tipped scissors
can be used to clip and remove infected hairs from around individual lesions.
Be sure to clip a wide margin around the lesion. If the strain of M. canis is
strongly fluorescent, a Wood's light can be used during treatment to monitor
resolution of the infection and locate hairs for removal.
Step 2: Selecting appropriate topical therapy
Topical antifungal therapy is recommended in all cats with positive fungal culture results and pending culture results in cats in contact with infected cats. The advantages of topical therapy are decreased overall length and cost of treatment, minimized spread of infective spores into the environment and removal of infective crusts, scales, and spores from the coat. The disadvantages are that cats hate to be bathed, dipped, or sprayed; topical and topical antifungal agents can be irritating to people and cats.
Whole-body topical antifungal therapy
The following recommendations for topical therapy are based on a review of both in vitro and in vivo studies.1-13 In vitro studies involve exposing either mats of infected hair or isolated infected spores to known dilutions of topical antifungal agents for specific periods. The viability of fungal spores is then determined by routine fungal culture of infective material. This technique has provided valuable efficacy information about various commonly used antifungal compounds and is a useful screening tool for potential commercial products.
Effective products
Lime-sulfur, enilconazole, miconazole, and bleach have been shown to be antifungal in in vitro or in vivo studies or both. It is important to note that fungicidal efficacy does not imply that one application of any of these products is 100% fungicidal. These products are fungicidal with repeated application.
Lime-sulfur (LymDyp-DVM Pharmaceuticals; 8 oz/gal water) has consistently been found to be antifungal in in vitro studies.2,3,6 In our facility, lime-sulfur has been used as the topical therapy of choice, and in some cases as the sole therapy, for treating research cats that are still infected or have positive culture results at the end of a study. I have found it to be consistently effective. Furthermore, I've supervised the eradication of dermatophytosis in a pet store with more than 30 infected kittens and cats. Financial constraints resulted in lime-sulfur being used as the sole therapy in most cats. Diligent environmental decontamination and twice-weekly sponge-on dips performed by the owner eradicated the infection. Lime-sulfur is administered twice a week and is the preferred treatment when enilconazole is not available or licensed for use. Lime-sulfur stains the coat of white cats yellow-green. It can be irritating to mucous membranes, and cats should be prevented from grooming the wet solution. Clients and cats tend to dislike the odor, but the odor rapidly diminishes once a cat dries. Owners should wear protective clothing, gloves, and a mask and should apply the dip in a well-ventilated area. It is important that clients do not rinse this product off the coat.
Enilconazole topical solution (Imaverol Janssen Pharmaceutica) 10% concentrated solution (100 mg/ml) is effective against M. canis. Unfortunately it is not available in the United States, nor is it approved for use in cats. A different formulation of enilconazole, licensed for use as an environmental disinfectant, is available in the United States (Clinafarm EC, 0.2% emulsion Janssen Pharmaceutica). This formulation has been used off-label to treat dermatophytosis at a dilution of 55.6 ml/gal water as a topical antifungal.8-11 It is important to note that using this product off-label is illegal since this is an EPA licensed product in the United States.
Because of the efficacy of enilconazole in treating canine and equine dermatophytosis, it has been the subject of many studies evaluating its safety and efficacy in cats 8-10 In two studies, it was used as the sole therapy for dermatophytosis; cats required at least 10 weeks of twice-weekly topical therapy before being cured, but fungal culture results were reported to be negative as early as five weeks into therapy. Enilconazole was well tolerated by all the cats but may have been associated with hypersalivation, anorexia, weight loss, emesis, idiopathic muscle weakness, and slightly elevated serum alanine aminotransferase activity. Longhaired cats made up most of the cats in these studies.
Miconazole (Malaseb-DVM Pharmaceuticals), as a sole therapeutic agent or in combination with chlorhexidine, has been shown to be an effective antifungal agent in both in vitro and in vivo studies.4,5,7,12,14 It is important to note that in the in vivo studies it was used twice a week as an adjuvant to systemic therapy. Miconazole shampoo needs a contact time of 10 minutes; this is essential for a therapeutic effect. This product can be irritating to the eyes and can cause skin irritation.
A 1:10 dilution of household bleach in water is an effective antifungal agent,
but it is not recommended as a topical antifungal agent. It is too irritating
to be used safely on cats and is not licensed for use in animals as a topical
agent. Furthermore, at this concentration it presents a human health hazard
because of its potential irritancy.
In general, the most consistently effective antifungal topical agents are lime-sulfur,
enilconazole, and miconazole. Twice-weekly application as a whole-body rinse
or shampoo (depending on the formulation) is recommended. Topical therapy is
best used in conjunction with systemic antifungal drugs. If topical therapy
is used as a sole therapy, clip the coat and use lime-sulfur. Do not allow cats
to lick or groom off the antifungal solutions.
Ineffective products
Captan, povidone-iodine, and chlorhexidine have been consistently found to be ineffective against M. canis in in vitro and in vivo studies.3 Chlorhexidine solution used as a dip was evaluated as the sole topical therapy in a controlled study using an experimental M. canis infection model. 13 In that study, infected cats received the dip treatment twice a week for 150 days after their coats were clipped. At the end of therapy, there was no significant difference between the chlorhexidine treatment group and the control group.
Local topical therapy
Topical antifungal ointments and lotions are not recommended for treating feline dermatophytosis. The efficacy of these products is unproved in feline dermatophytosis. Furthermore, studies in guinea pigs revealed that topical antifungal agents were only successful in eliminating the infection when it was confined to the glabrous skin.15 Using these products was also associated with the development of chronic dermatophytosis. From a more practical perspective, these lotions and ointments are messy, easily groomed off, and tempt clients to do spot therapy. Given the fact that infective spores are present throughout the coat, applying local topical agents is not effective or practical therapy.
Step 3: Selecting appropriate systemic therapy
Systemic therapy is the treatment of choice for feline dermatophytosis. The efficacy of griseofulvin, itraconazole, terbinafine hydrochloride, and lufenuron alone or in combination with other therapies has been studied. 5,7,9,10,12,16-29 I am not aware of any age-related studies, but I do not use any of the systemic antifungal agents in kittens less than 8 weeks of age unless the alternative is euthanasia.
Griseofulvin
Griseofulvin is a fungistatic antifungal agent that inhibits nucleic acid synthesis and cell mitosis metaphase by interfering with the function of spindle microtubules. Griseofulvin has variable absorption from the digestive tract; its absorption is enhanced by administering it with fatty meat or by using formulations containing polyethylene glycol.
This drug is teratogenic and should not be given to pregnant animals. There are also anecdotal reports of its interfering with spermatogenesis, so it is best avoided in breeding males.14 The most common adverse effects are anorexia, vomiting, and diarrhea, which can be managed by dividing the dose into twice-daily administrations. Bone marrow suppression and neurologic side effects are most likely idiosyncratic reactions. Do not use griseofulvin in cats that have feline immunodeficiency virus (FIV) infections, because severe neutropenic reactions have been seen in cats with FIv.20
The most commonly used dosing regimen is daily: griseofulvin microsize at a
dosage of 25 to 50 mg/kg given orally once a day or divided twice a day; griseofulvin
ultramicrosize at a dosage of 5 to 10 mg/kg given orally once a day or divided
twice a day. Higher doses may be needed in refractory cases. Itraconazole is
rapidly replacing griseofulvin as the drug of choice for treating dermatophytosis.
Itraconazole
This drug is currently my first choice for treating feline dermatophytosis. Itraconazole (Sporanox Janssen Pharmaceutica, Ortho Biotech) is a triazole derivative that alters fungal cell membrane permeability by inhibiting ergosterol synthesis.30 At low doses it is fungistatic, and at higher doses it is fungicidal. In general, itraconazole is well-tolerated by cats at the doses used to treat dermatophytosis. vomiting and anorexia are the most common adverse effects and, in my experience, are dose-related.
Itraconazole's antifungal activity against M. canis has been documented in people and guinea pigs for some time. Three studies involving multicat situations provide some interesting insights regarding effective flexible dosing schedules. 16,17,19 Based on these studies, the following dosing regimens can result in a mycological cure, provided they are accompanied by concurrent clipping, topical therapy, and environmental decontamination procedures.
It is important to point out that the study of short-term cycle therapy used a dose of 1.5 to 3 mg/kg given orally once a day.16 I recommend a higher dose of itraconazole (10 mg/kg orally), because only eight of 15 cats in that study were cured of dermatophytosis. I have found the 15 day treatment cycles to be very effective in multicat situations, provided a higher dose is used. I prefer the 10 mg/kg dose, but I have successfully treated dermatophytosis with doses of 5 to 10 mg/kg given orally.
Terbinafine
Terbinafine (Lamisil Tablets-Novartis) is the newest systemic antifungal agent to be used in treating dermatophytosis. It is an allylamine antifungal agent that suppresses the biosynthesis of ergosterol by inhibiting the fungal enzyme squalene epoxidase.31 The drug is considered to be fungicidal against dermatophytes.
Five recent reports describe its use in treating dermatophytosis in multicat
situations; two of these studies report on different aspects of the same experimental
infection.18,21-25 In addition, this drug has been used in a recently completed
study at the University of Wisconsin (DeBoer, D.J.; Moriello, K.A.: Unpublished
data, 2003). As a result of these studies, it has been determined that terbinafine
needs to be administered at a dose of 30 to 40 mg/kg given orally once a day.
This dose results in significantly higher concentrations in hair when compared
with lower doses. Terbinafine at this dose may be substituted for itraconazole
in combined continuous/pulse or short-term cycle therapy. Terbinafine also appears
to be equivalent to griseofulvin and itraconazole in
treating feline dermatophytosis (De= Boer, D.J.; Moriello, K.A.: Unpublished
data, 2003).18 It is well-tolerated by cats; vomiting is the most common adverse
effect. In my opinion, there is not an advantage in using terbinafine instead
of itraconazole in cats.
Lufenuron
Lufenuron is a benzoylphenylurea drug that disrupts chitin synthesis and is used for flea control. Chitin is a critical component of the outer cell wall of fungi, and it is possible that drugs that disrupt chitin synthesis might also have antifungal activity. One retrospective study suggested lufenuron treatment was strongly associated with recovery in many dogs and cats with a number of fungal infections, including dermatophyte infections.26 Since that report, the use of lufenuron has been a widely debated topic in both the lay and veterinary literature and has been the focus of numerous anecdotal and published reports.9,27-29
Two controlled blinded studies have evaluated the efficacy of lufenuron in preventing or altering the course of experimentally induced M. canis infections.28,29 In the first study, after two months of pretreatment with either 30 or 130 mg/kg lufenuron given orally, kittens received a markedly larger than field challenge with infective M. canis spores.29 In the second study, cats received four doses of lufenuron (100 to 133 mg/kg orally or 40 mg/kg subcutaneously) at monthly intervals before being exposed to a subclinically infected cat.28 They then received five additional monthly doses. In the second study, infections were established more slowly in the lufenuron-treated groups when compared with the control group, but the infections in all groups resolved at about the same time.28 In both studies, lufenuron failed to prevent infection or alter the course of infection.28,29
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Table 1 - Treatment Recommendations for Feline Dermatophytosis Administer topical antifungal therapy twice weekly - The most effective topical antifungal agents are lime-sulfur, enilconazole, and miconazole, lime-sulfur is suitable for sole therapy; combined topical and systemic therapy is the treatment of choice. Administer systemic antifungal therapy - Griseofulvin, itraconazole (preferred), and terbinafine hydrochloride have been shown to be the most effective. Consider fungal vaccination - This may be a useful adjuvant therapy along with topical, systemic, and environmental control or a practical alternative to topical therapy in situations in which topical therapy cannot be used. The continued availability of commercial fungal vaccines is unknown at this point. Treat cats until you attain a mycological cure - Keep in mind that cats will be clinically cured before they are mycologically cured. |
In a clinical field study involving 100 cats in two catteries with naturally occurring dermatophytosis, lufenuron (60 mg/kg orally once on Day 0 and again on Day 30) was used in conjunction with topical enilconazole. A second group of cats was treated with griseofulvin (25 mg/kg b.i.d.) and topical enilconazole. Although the investigators reported a decrease in fungal culture counts over 90 days and clinical resolution of signs, cures were not reported in either group. The authors did note that severe environmental contamination was present in the catteries 9 At this time, I do not recommend lufenuron for treating or preventing dermatophytosis.
Fungal vaccines
Intense interest in developing a fungal vaccine to prevent and possibly treat dermatophytosis continues. The only commercially available fungal vaccine licensed for use in cats is Fel-O-Vax MC-K (Fort Dodge Laboratories), and its current availability is uncertain. Several studies have evaluated either an experimental or commercial vaccine for treating and preventing dermatophytosis.32-37 These studies have found that fungal vaccines are not protective against challenge exposure, but they are associated with a temporary reduction in the clinical signs of dermatophytosis. Fungal vaccines as sole therapy are not effective in treating dermatophytosis, but they may be a useful adjuvant therapy when combined with appropriate topical and systemic therapy and environmental control. Fungal vaccination may be a practical alternative to topical therapy in situations in which topical therapy cannot be used; this recommendation assumes that the coat is clipped and that appropriate systemic antifungal therapy and environmental decontamination procedures are used.
Treatment summary and follow-up
The treatment strategies described in this article are summarized in Table 1. Ridding cats of dermatophytosis for good requires intensive monitoring and environmental decontamination. The best way to go about these two important components of therapy, as well as how to prevent reinfection, is covered in the next article in this symposium.
References
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