Monitoring Treatment and Preventing Reinfection in Cats with Dermatophytosis
Vet Med 98[10]:886-890 Oct'03 Symposium 4 Refs
Karen A. Moriello, DVM, DACVD
Dept of Medical Sciences, SVM, University of Wisconsin-Madison, Madison, WI 53706

ABSTRACT:
Now that you've diagnosed dermatophytosis and formulated a treatment plan, make sure it works. This involves monitoring the cat throughout treatment and extensively decontaminating its environment.

FULL TEXT:
In this final symposium article, I discuss practical steps to take when treatment fails, proper treatment monitoring, environmental decontamination, and reinfection prevention.

Causes of treatment failure

After you have outlined the treatment plan with owners of cats with dermatophytosis and have provided an estimate of the cost for 56 to 100 days of therapy, it is helpful to discuss causes of treatment failure before discussing monitoring, decontamination, and reinfection prevention plans. Feline dermatophytosis is expensive to treat, and it is best to forewarn owners of possible obstacles to resolution as well as help them see what they can do to facilitate the quickest response to therapy.

In my experience, the most common causes of treatment failure are

• An incorrect diagnosis. This most commonly occurs when clinical signs alone are used to make a diagnosis, underscoring the need to definitively diagnose dermatophytosis based on a positive fungal culture result alone or in addition to a positive result on direct microscopic examination of hairs.
  
  
• Reinfection. This most commonly occurs when a cat is exposed to a contaminated environment or to other cats with positive culture results, such as those that are sub clinically infected or carriers.
  
  
• Environmental decontamination is extremely important in the treatment process, not unlike treating the environment in flea infestation cases. And the more animals involved in the outbreak, the greater the environmental contamination.
  
  
• A contaminated environment. This can cause consistently positive culture results or fluctuations between negative and positive culture results, especially if only a few colonies are present on the fungal culture plate.
  
  
• Resistant organisms. It is unknown how often resistance occurs. Most of the cases of resistance I have investigated on referral have been related to owner compliance problems; incorrect drug doses; drug intolerance by a cat; the inability to medicate cat; or exposure to carrier cats, contaminated environments, or persistently infected cats. Each of these causes, with the exception of drug intolerance, should be investigated before making changes in antifungal drug therapy. In cases of drug intolerance, consider changing to a divided-dose schedule or a different drug.
  
  
• Concurrent illness, certain medications, or a defective immune system. Concurrent systemic illnesses are usually more obvious than defective immune systems. Common concurrent illnesses or therapies that can complicate resolution of dermatophytosis include hyperthyroidism, diabetes mellitus, chronic renal failure, neoplasia or chemotherapy, glucocorticoid administration, demodicosis, and infection with feline leukemia or feline immunodeficiency virus.
  
  
• Refusal to clip medium-haired or longhaired cats or any cat with generalized dermatophytosis. Unfortunately, many owners become convinced of the need to clip their cats' coats only after treatment takes longer than expected or infection persists.
  

Monitoring treatment

Dermatophyte infections in cats usually resolve without treatment within 60 to 100 days if the cats have competent immune systems. If a cat is ill or has a defective immune response, infection can persist for an indefinite period. Cats receiving topical and systemic antifungal therapy usually show a marked improvement in clinical signs within two to four weeks of starting therapy. It may take months for the entire coat to regrow if the infection is severe and the coat has been clipped. But after treatment is initiated, there is usually a noticeable decrease in pruritus, scaling, erythema, and hyperpigmentation, with hair growth following shortly thereafter.

Recheck examinations

Begin monitoring therapy four weeks after initiating treatment (Table 1). Examine patients every two to four weeks. Have the owner transport the cat from home directly to the examination room in a disinfected cat carrier to minimize hospital contamination. The carrier should he covered: this is easily accomplished by placing the carrier inside You can perform a Wood's pillowcase light examination to screen for infected hairs, assuming the dermatophyte strain is fluorescent. Remove any infected hairs you find Finding infected hairs on the face, ears, or muzzle suggests an owner may be having difficulty applying topical therapy or is hesitant to apply topical solutions to the cat's face and ears. In multicat households or catteries, infected hairs on a cat's face, ears, or muzzle may suggest exposure to another infected cat. I have found that dermatophyte lesions it multicat facilities often first occur or the face, because muzzle-to-muzzle contact and head rubbing are common behaviors.

During the recheck examinations, perform fungal cultures. Perform the first toothbrush fungal culture four weeks after initiating antifungal therapy, and then perform a culture every two weeks thereafter. Fungal cultures can be performed more frequently, but this increases the cost of treatment and monitoring. Hold the fungal cultures for 21 days, because successful treatment results in successively fewer viable fungal spores on the coat, and their growth is often slow. A fungal culture can be discarded as soon as the plate shows growth or indicates a negative result on Day 21.

As soon as the first negative fungal culture result is obtained, begin performing weekly fungal cultures. Two consecutive negative fungal culture results are usually sufficient in single-pet situations, but I recommend continuing systemic therapy until you obtain three consecutive negative fungal culture results in multicat situations. When this goal is achieved. discontinue therapy if the cat can be removed from the facility and placed in a clean environment. I this is not feasible, discontinue systemic therapy, but continue topical therapy until all cats have negative fungal culture results to minimize the risk of reinfection.

Toothbrush cultures can be ex pensive in large catteries, so a reasonable alternative is to perform a culture in all cats four weeks after initiating therapy and every four weeks thereafter. Because it can take up to 21 days for growth to occur, make sure the cattery operator understands that the results of the fungal culture you are discussing reflect what was present on the coat up to three weeks ago. It is also advisable to culture the environment before discontinuing therapy in catteries or multicat situations. This is easily accomplished by performing toothbrush cultures of cat rooms, bedding, furniture, and toys.

Guidelines for fungal culture interpretation

Large numbers of colonies with classic gross and microscopic appearances are typically found on toothbrush cultures from untreated cats or cats early in the course of infection. The number of fungal colonies tends to decrease as the infection resolves.

Cats that have fluctuating fungal culture results (e.g. negative to positive to negative), especially with fewer than five to seven colonies per plate, are usually carriers. This has been a consistant finding in our dermatophytosis research studies. To confirm this, place the cat in a clean cage, allow it to groom for several days to remove spores, and then repeat the fungal culture. If a cat is truly a mechanical carrier, dust with spores will be removed by grooming during this confinement period. Alternatively, you can wipe the cat's coat with a damp towel to remove dust and spores before performing a culture. We have not had false negative culture results when using this technique in cats with subclinical infections. If there is any doubt about the cat's fungal status, continue treatment. It is important when performing cultures to brush the cat's entire body until hair is trapped in the toothbrush bristles.

Environmental decontamination

Microsporum canis can persist in the environment for long periods; spores have been viable in my laboratory for up to two years. The spores are microscopic and can be spread easily by air currents and contaminated dust and through heating ducts and vents. In my opinion, contaminated environments are underrecognized in their importance as reservoirs of infection in people and other cats. The amount of environmental contamination is directly related to the number of cats involved in the outbreak and the amount of time the cats spend in the home or cattery before the infection is recognized. The baseline cleanliness of the facility is also a factor. Table 2 lists environmental decontamination recommendations for pet owners.

In most cases of a single pet cat with dermatophytosis, the pet is a kitten or an adult cat acquired from a shelter or cat rescue agency, and the infection is identified fairly soon after the cat is obtained. Have the owner keep the cat or kitten in a small, easily cleaned room (e.g. bathroom) that does not have carpeting. The cat should be quarantined in this room until it has received systemic antifungal therapy for at least 15 days and a minimum of four whole-body dips in lime-sulfur. At this point, the cat can be given greater access in the home, ideally in uncarpeted and easily cleaned rooms if the owner is unwilling to confine the kitten. In most cases, thorough and repeated vacuuming and scrubbing of surfaces on a daily basis should prevent contamination of the home. Cat beds and blankets should be washed daily in hot water and bleach. Bathrooms and nonporous surfaces can be disinfected with a 1:10 bleach solution. Routine cleaning and disinfection of the home should be continued until the cat is mycologically cured.

In most cases of dermatophytosis in multicat households, a kitten or young cat is added to the household and is later found to have dermatophytosis. In some cases, an adult cat is added. The introduction and assimilation of a new cat in an established group usually takes several weeks, and the infection in the new member is usually noticed before the other cats have an opportunity to become very social with the new addition. Lesions on the existing cats are often first seen on the face, nose, periocular area, and ears and in the hairs in the bell of the ear. Screening fungal cultures of the housemates will indicate how contaminated the environment is. If only the new cat has positive culture results, then environmental contamination is probably low. If more than one other cat has positive culture results, aggressive decontamination is indicated. In our studies in which we have added an infected cat to a group of four to eight young cats, the first cats to have positive culture results are usually the most social cats. If the more reserved cats in the colony had positive culture results, we found that the environment was heavily contaminated, which was confirmed on routine culture of the environment. Once again, this underscores the importance of keeping a new cat confined to an area that is easily cleaned.

Consider all catteries to have a high degree of environmental contamination regardless of the number of cats initially diagnosed with dermatophytosis. Aggressive decontamination is recommended.

Environmental disinfectants

A disinfectant is a germicide that inactivates virtually all recognized pathogenic microorganisms on inanimate objects, but not necessarily all forms of a microorganism. Disinfectant label claims of fungicidal activity against dermatophytes are determined by testing the compound against the mycelia' form of a dermatophyte and not against the naturally infective state (i.e. infected hairs and spores).^2,3
Lime-sulfur (1:33), enilconazole (20 µl/ml), and bleach (1:10) are consistently effective when used at the recommended dilution. In one study, lime-sulfur and enilconazole were 100% fungicidal even when the recommended concentration was diluted to one-fourth the recommended concentration.⁴ Enilconazole (Clinafarm EC and Clinafarm SG-American Scientific Laboratories, Janssen Pharmaceutica is most commonly used in poultry facilities to disinfect the premises for Aspergillus organisms and is licensed by the EPA. If used off label to disinfect facilities heavily contaminated with M. canis, the spray or fogger should be used as recommended with respect to human exposure and precleaning the environment. This product is corrosive and harmful or fatal if ingested.

Chlorhexidine and Virkon S (Antes International) are not recommended for use as fungicidal disinfectants. In the same study, they were ineffective even when used at four times the manufacturer's recommended dilution.⁴

Preventing reinfection

The risk of reinfection for a single pet cat and cats in a multicat household is relatively low if they live solely indoors. The most likely sources of exposure in these situations are the addition of a new cat or exposure to other infected animals at boarding and grooming facilities or even veterinary hospitals. The spore exposure load in cats exposed to other infected animals outside the home would most likely be small. A healthy cat that routinely grooms itself should be able to mechanically remove spores. All new cats and dogs in a household should be screened for dermatophytosis. If the pet originates from a pet store or animal shelter, it should be treated with topical lime-sulfur until the culture results are known.

The risk of reinfection for cattery cats depends on whether the cattery is open or closed. (This assumes that all cats were mycologically cured and that the environment was decontaminated.) The following recommendations are for operators of catteries:

• Randomly obtain fungal culture samples from cats and the environment to screen for dermatophytosis. If positive fungal culture results are found, obtain culture samples in all cats.
• Obtain fungal culture samples in all cats returning from shows, breeding loans, or exchanges. Also bathe these cats in a grooming shampoo or rinse them in water, and then dip them in lime-sulfur before returning them to the colony. If a cat has been gone for more than a few days or is longhaired, consider quarantine until culture results are known.
• All new additions should have negative fungal culture results in the last month before being added to a cattery. Obtain a fungal culture sample in these cats upon entry, treat them with a topical antifungal solution, and isolate them until the fungal culture results are known.
• Follow strict cleaning and disinfection protocols. Many of the steps involved in the disinfection of the environment can be adapted to cattery facilities. Intermittent fogging with enilconazole is recommended where permitted.
• Routinely (at least once a month) obtain culture samples from the environment to look for dermatophytes. You can purchase inexpensive toothbrushes at discount stores to collect the samples.
• At shows, cover cat carriers with cloth to prevent spores from contacting the coat by way of air currents.
• Visitors to the cattery should wear protective clothing and should not be allowed to have contact with cats if there is a risk they may be mechanically carrying spores.

References
1. Rutala, WA.: Guidelines committee: Draft APIC guideline for selection and use of disinfectants. Am. J. Infect. Control: 2335A-67A; 1995.
2. Official Methods of Analysis of the Association of Official Analytical Chemists, 13th Ed. Association of Official Analytical Chemists, Washington, D.C., 1980; p 56.
3. Scott, E.M. et al.: An assessment of the fungicidal activity of antimicrobial agents used for hard-surface and skin disinfection. J. Clin. Hosp. Pharm. 11 (3):199-205; 1986.
4. Moriello, K.A. et al.: Determination of strain variability of Microsporum canis to disinfectants (abst.). Vet. Dermatol. 13:225; 2002.

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