Ringworm: Dermatophytosis

What is Ringworm?

Ringworm, also call feline dermatophytosis, is not a worm. It is a fungal infection of the hair and skin. Microsporum canis is the most common cause of ringworm in cats. Two other fungal organisms can cause a ringworm infection, Microsporum gypseum and Trichophyton species. Ringworm infections are more common in cats than dogs. Persian cats are more likely to get ringworm than other cat breeds.

Clinical Signs

Ringworm lesions are variable in cats and can mimic many other skin diseases including allergies, mites, skin cancer, etc. Symptoms range from a very mild, undetectable infection (asymptomatic carriers) to severe lesions all over the body. Often you will see areas of hair loss (alopecia), redness of the skin, scaling, broken hairs, or crusting. Lesions are often found on the head but can occur anywhere on the body. Sometimes ringworm can be itchy, but not always.

Diagnosis

Your veterinarian will want to rule out other causes of your cat’s skin lesions, as well as test for ringworm. A fungal culture or PCR is needed to definitively diagnose dermatophytosis.

• Wood’s Lamp Examination: A Wood’s Lamp is a UV light that can be used to examine suspected ringworm lesions. This is an easy screening test; however, not all ringworm species will glow under the light. We can get false positive and false negative results with the Wood’s Lamp. Additional diagnostics are always needed to evaluate for ringworm infections.

• Direct Examination: Direct examination is done by plucking some hairs and examining them under the microscope. Fungal hyphae may be visible on the hair shafts.

• Fungal Culture: Fungal Culture is done by plucking hairs from a suspected ringworm lesion or using a toothbrush to comb hairs from the body. The hairs are placed on a special medium and monitored for 14 days. If a fungal organism grows, the medium changes to a red color. The lab will then identify which organism is present.

• Ringworm PCR: Polymerase Chain Reaction (PCR) detects the DNA of fungal organisms in the submitted sample. The test is much faster than a culture (usually 1-3 days for results) but is very sensitive. A positive result can be obtained with infection, or with non-viable organisms still present on the skin after treatment. PCR is a great way to diagnose ringworm; however, it is not typically used to monitor for treatment efficacy.

• Skin Biopsy: Sometimes ringworm lesions present in an unusual way. Occasionally, a skin biopsy is done to rule out other causes of lesions, including allergies and cancer. Ringworm can be seen on biopsies and can confirm a diagnosis.

Treatment

Treatment most often involves a combination of topical and systemic therapies. Your veterinarian will discuss the right treatment course for your cat based on the symptoms and your cat’s overall health. The course of treatment varies among cats but can take up to 6 months to achieve a cure. Most cats will resolve in less than 3 months.

Topical

• Lime Sulfur Dips – This is the recommended topical therapy for treating dermatophytosis. The dip has a strong sulfur smell. It is applied as a rinse twice a week and allowed to air dry. The dips can be done at home or at the veterinary clinic.

• Accelerated Hydrogen Peroxide Rinse – This has not yet been studied as a treatment for ringworm. Anecdotally, this rinse has been used every 2 days in combination with systemic treatment.

• Eniconazole rinses – currently not available in the U.S.

• Miconazole Shampoo – Miconazole has not been shown as an effective treatment alone but can be used as a twice weekly shampoo in conjunction with systemic therapy.

• Climbazole mousse – This can be used 2-3 times weekly topically.

Systemic

• Itraconazole – Itrafungol is an FDA approved medication used for treatment of dermatophytosis. It is used once daily for 7 days, stop for 7 days, repeat for total of 3 weeks treated. Generic and compounded formulations are not recommended as they are not absorbed well. Side effects are dose related and usually seen with higher doses than we prescribe. Side effects include anorexia, vomiting, weight loss, elevated liver values, and jaundice.

• Fluconazole – This is extra-label and is given twice daily. Side effects are similar to itraconazole.

• Terbinafine – This is extra-label and is given daily. The pill reportedly has a bad taste. GI upset, vomiting, anorexia, and diarrhea, are reported side effects.

• Ketoconazole – Historically was used for fungal infects; however, newer, safer products are preferred. Generally not prescribed anymore and some believe it is contraindicated in cats.

• Griseofulvin – Not recommended in cats due to severe potential side effects.

Follow Up

After starting treatment, your veterinarian will want to follow up in 1 month to recheck the skin and repeat the fungal culture. A fungal culture should be done every 2 weeks until there are at least 2 consecutive negative cultures.

Environmental Treatment

If your cat is suspected of having dermatophytosis, your veterinarian will recommend a plan for decontaminating the environment.

• Clean all nonporous surfaces with chlorine bleach (1:10) or accelerated hydrogen peroxide (Rescue™)

• Vacuum carpets daily

• All other surfaces should be wiped with a dry Swiffer Sweeper weekly

• Wash any bedding and fabric materials weekly (any cleaner can be used)

• Dispose of hard to clean things like cat trees, scratchers, collars, etc.

• Replace furnace filters regularly

Zoonosis

Ringworm can be transmitted from pets to people, as well as to other pets. It is very important to have any skin lesions on your cat examined by a veterinarian right away. If people in the house develop rashes or skin lesions, contact your physician right away. Anyone can become infected with ringworm; however, children, the elderly, pregnant women, and immunocompromised people are at higher risk of infection.

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