Chapter 4: Treating Ringworm

In most cases, pet animals spontaneously recover from ringworm within about 3 months. Awaiting self-cure is certainly a reasonable choice in a single animal household with no young children or immunocompromised adults where contagion is not a major concern. However, in a shelter environment or foster situation, a more rapid resolution is highly desirable. Reducing environmental contamination is just as important as treatment directed towards speeding recovery of affected animals.

A truly awesome resource on dermatophyte culture and treatment:

Sandra Newbury, DVM and Karen A. Moriello, DVM, DACVD from the School of Veterinary Medicine at the University of Wisconsin-Madison have conducted an ongoing study of naturally occurring shelter ringworm to develop cost-effective systems for screening and treatment. As a result of their findings Drs. Newbury and Moriello developed Dermatophyte Treatment in a Nutshell, a document that details diagnostic and treatment strategies they have found most effective in a shelter environment.

Topical Treatments

The most important component of treatment in a population is topical therapy. 

This is critical in order to reduce immediate and ongoing environmental contamination. This is best accomplished through the use of topical therapy which sterilizes the coat and prevents the further growth of spores that can re-contaminate the environment.

Of all available topical therapies, lime sulfur solution is the most effective as it sterilizes the coat to prevent further growth of ringworm, is relatively easy to apply rapidly to a number of cats, and has been documented to work well in a shelter setting.

Miconazole shampoo in combination with chlorhexidine may also be effective; chlorhexidine alone is not. Enilconazole solution, although reportedly effective, is not available for this use in the United States (it is regulated by the EPA rather than the FDA, which does not permit off-label use in the same way). Some currently available topical treatments are ineffective or only partially effective; use caution if selecting another treatment other than lime sulfur solution. Chlorhexidine shampoos and locally applied topical ointments do not effectively sterilize the coat or provide residual activity against further growth. Topical terbinafine (Lamisil) and clotrimazole (Lotrimin), are not recommended for use in pets as they do not reduce further growth of ringworm lesions.

Pure Oxygen® Shampoo (accelerated hydrogen peroxide shampoo by Ogena Solutions) may eliminate ringworm spores from the coat. More studies are needed to determine the efficacy of Pure Oxygen® Shampoo as a topical treatment for ringworm.

Lime Sulfur Use

  • Use 8% concentration (note: this is 8oz per gallon of warm water, twice the recommended concentration listed on the bottle).
  • Apply twice weekly throughout treatment.
  • Safe to use on pregnant and nursing animals and kittens/puppies > 2-3 weeks old.
  • Wipe nursing moms’ teats clean after topical treatment, keep juveniles warm with a heating lamp or warming blocks if necessary.
  • E-collar afterward is not necessary.
  • Do not pre-wet the animal.
  • Consider using a new garden sprayer for application: details can be found on the Dane County Humane Society dermatophyte treatment web page.  Be sure to keep sprayer end close to the animal's skin when applying.
  • Use a small rag or sponge to apply solution on face, nose and ears.
  • Use of ophthalmic lubrication ointment to protect the cat’s eyes is not recommended because if the solution gets into the eye it can be very difficult to remove the solution if it is mixed with lubricant.  Instead, keep eye flush handy and flush generously if solution gets into cat's eye.
  • Do not rinse the animal after solution application; wrap the animal in a towel and leave to dry.

Please note: physically dipping cats in the lime sulfur solution is not recommended as this is stressful to the cats (and staff) and can lead to cross contamination between cats being treated if the same lime sulfur dip solution is used on multiple cats.

Systemic treatment

Systemic treatment is an important adjunct to topical therapy, especially in a shelter where time-to-cure is an important consideration. Extended stays in a shelter or foster care increase the chance of spread, use precious isolation space, and may reduce the adoptability of the patient, especially if kittens are allowed to grow old in treatment.

The drawbacks of systemic treatment are the relatively high cost of the drugs and the possibility of toxic side effects. Itraconazole is a good choice due to its demonstrated efficacy, relative safety, and long half-life in the skin. We do not recommend compounded itraconazole as it has repeatedly been shown to be less effective and may result in treatment failure.

Fluconazole and terbinafine are also reportedly effective. Griseofulvin is effective, but more likely than itraconazole to cause toxic side effects. Ketoconazole should be avoided in cats if possible, as it can cause hepatotoxicity in this species. Lufenuron (Program) has been shown in repeated studies to be ineffective.  

Animals on any systemic antifungal should be closely monitored, and all directions for administering the drugs carefully followed. These drugs should be avoided in pregnant animals. 

Clipping and Shaving

Clipping is often unnecessary in short and medium haired cats, and may worsen lesions through micro-trauma and mechanical spread of spores. However, clipping is indicated for very long haired cats and those that may be unable to groom due to conformation (e.g. Persians), concurrent severe upper respiratory congestion, or matted coat. Clipping may also be useful in cats whose coats simply become unmanageable after dipping.

Clipping should be performed gently with a #10 blade, taking great care to avoid clipper burn, and hair should be carefully disposed of. Clipping with a closer blade causes excessive trauma and increases the chance of worsening lesions. Clipping should be performed in a room that is easily cleaned since it causes heavy environmental contamination, and instruments used should be carefully cleaned and dedicated only to that purpose, never used on healthy animals (i.e. do not use the surgery clippers for ringworm cats!).

It is important to wear protective clothing whenever handling a ringworm animal in a shelter, and especially when clipping. In a facility with an easily cleaned/disinfected euthanasia room, this might be a good place for clipping ringworm cats.

Treatments That Do NOT Work

Although many treatments are reportedly effective for individual animals, the frequency of self-cure makes these claims somewhat difficult to assess in the absence of supporting scientific evidence. In a population setting, treatment failure is more evident and common, and the requirements for highly effective treatment are rigorous. The following treatments have failed to demonstrate efficacy in controlled studies:

  • Lufenuron (Program)
  • Topical creams and ointments
  • Chlorhexidine as a shampoo or disinfectant
  • Potassium peroxymonosulfate (Trifectant) as a dip

“Natural” treatments often suggested on well-meaning pet websites such as apple cider vinegar, coconut oil, tea tree oil, papaya, garlic, grapefruit seed extract, colloidal silver, betadine, and topical bleach are not effective and some of these home remedies are toxic to pets.

Pulse therapy is complicated and difficult to keep track of in a shelter setting. It requires a loading dose and ultimately does not reduce the amount of drug used in treatment. Therefore, pulse therapy is not recommended.

Verifying Cure

It is imperative to recognize that animals can still carry infective fungi even after signs appear to have completely resolved. Animals may be considered cured after 3 consecutive weekly fungal cultures are negative. (If twice weekly lime sulfur and systemic itraconazole are used, 2 cultures may be adequate).

Fungal culture should be obtained, using the toothbrush collection method, starting at week 1 of treatment. Animals housed in a contaminated environment may become incidentally contaminated.  If this is a concern, the animal should be kept in a clean cage or room for 5-10 days prior to obtaining the culture.

Because the fungal cultures take about two weeks to verify negative results, this means that treatment and documentation of cure will take a minimum of 6-8 weeks, and may take as long as 3-4 months. Housing and socialization of the animal during this period are extremely important considerations when deciding whether treatment in the shelter is practical. 

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