Treatment of Dermatophytosis

Chapter 105


Treatment of Dermatophytosis




Dermatophytosis is caused by a superficial fungal disease that infects keratinized tissues (hairs, claws, or stratum corneum). It is a skin disease of zoonotic importance. The most common cause of dermatophytosis in cats is Microsporum canis; dogs may be infected with M. canis, Microsporum gypseum, or Trichophyton mentagrophytes. Recently, infections in cats with Microsporum persicolor or Trichophyton spp. have been reported.


Dermatophytosis is more common in cats than in dogs. Hair loss, scaling, and crusting are frequent clinical findings. In cats the disease can mimic many skin diseases; therefore fungal cultures are a reasonable core diagnostic test. In dogs the typical circular alopecic lesions of bacterial pyoderma often are mistaken for dermatophytosis. Dermatophytic kerion reactions appear as nodular or draining lesions that may mimic deep bacterial pyoderma. Infections may be subtle, especially in long-haired cats and small dogs such as Jack Russell terriers and Yorkshire terriers.



Important Points to Remember about Diagnostic Tests


Wood’s lamp examination is most useful to identify potentially infected hairs (which show bright apple-green fluorescence) for culture or for direct examination. Direct microscopic examination of hairs for ectothrix spores is recommended only for hairs that show fluorescence under Wood’s lamp. Skin biopsy is necessary only for confirmation of fungal kerion reactions or pseudomycetoma. Fungal culture must still be performed to confirm the presence of dermatophytes. The most widely used fungal culture medium is dermatophyte test medium (DTM), which contains inhibitors of bacterial and saprophyte growth and a color indicator. A toothbrush is most commonly used for obtaining diagnostic specimens. The toothbrush is combed over the hair coat until the bristles are full of hair; comb lesional areas last. Cultures should be incubated between 24° and 30° C (75° and 86° F). Daily visual examination of inoculated plates allows rapid identification of highly suspicious colonies. On DTM, suspect pathogenic colonies are pale or white with a red ring of color developing around them as they grow. Microscopic confirmation is required (using either lactophenol cotton blue or new methylene blue stain) because some nonpathogenic fungi can turn DTM red. The reader can find help with microscopic identification in mycology textbooks or on websites such as www.doctorfungus.com. Most Microsporum pathogens grow within 7 to 14 days; however, cultures from animals undergoing treatment should be held for 21 days because treatment slows the growth of the organisms.



Treatment Principles and Options


In most healthy animals dermatophytosis is a self-curing disease. However, dermatophytosis is a public health concern and treatment is recommended to shorten the course of infection and minimize the chances of transmission. Treatment includes three key aspects:




Limiting and Controlling Contamination of the Environment


The authors recommend starting treatment discussion with instructions on how to limit the spread of spores because then it is easier for clients to understand and comply with treatment recommendations. It is critical to explain to clients that these spores do not multiply in the environment unlike mildew or other mold overgrowth and repeat cleaning minimizes the amount of infective material in the environment. Homes are readily decontaminated once the animal is cured or removed. The use of reasonable cleaning practices minimizes spore contamination (Box 105-1). The most important cleaning steps are gross removal of debris and aggressive detergent cleaning followed by rinsing with water (i.e., hard cleaning); disinfectants do not work in the presence of organic debris and can be inactivated in detergent residue.



Box 105-1   Recommended Environmental Control Measures in the Treatment of Dermatophytosis



For Households with One or a Few Animals



Confine pets to easily cleaned rooms. Close closets and drawers, and remove knick-knacks.


Thoroughly dust surfaces with Swiffer-type dusters and vacuum or use Swiffer-type sweepers on floors as often as possible but at least twice a week.


Wash hard surfaces with detergent and water as often as possible but at least twice a week.


Launder (hot water/hot dryer) rugs, animal bedding, and other pet contact bed linens.


Launder, disinfect, or discard pet toys and grooming aids.


If possible, disinfect hard floor surfaces with a product labeled as effective against Trichophyton spp.; allow 10 minutes of wetting time.


Vacuum (and disinfect if possible) any vehicles and transport cages used for animals.


After cure or removal of the animal, obtain culture specimens to check for contamination by wiping small squares of Swiffer cloths over exposed areas and using the surfaces of the cloths to inoculate fungal culture plates.

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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Treatment of Dermatophytosis
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