Clinical Exposures: Canine dermatophyte infection - Veterinary Medicine
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Clinical Exposures: Canine dermatophyte infection


VETERINARY MEDICINE


Microscopic examination of the fluorescing hairs may be confirmatory, but using a clearing agent (e.g. potassium hydroxide, chlorphenolac) on the hairs may increase the probability of finding fungal hyphae.4 Microscopic examination of skin scrapes by using a mineral oil suspension is not an effective screening test.1,4

Definitive diagnosis

Fungal culture and histologic examination are considered the gold standards for definitively diagnosing dermatophytosis. Both tests are good for screening and confirming disease, but neither test has 100% sensitivity or specificity.1,3,4

The fungal culture medium or dermatophyte test medium (Fungassay—Synbiotics, InTray DM—BioMed Diagnostics) contains inhibitors of bacterial and saprophytic growth and phenol red as an indicator of colony growth. The plates are observed for at least seven to 14 days, and an incubating temperature warmer than room temperature may be necessary for optimal growth. A color change (e.g. orange to red) of the dermatophyte test medium with concurrent visible colony growth supports the presence of fungal infection.1,4

Histologic examination is especially valuable in diagnosing nodular or granulomatous disease. Fine-needle aspiration of the nodules may reveal fungal hyphae, but histology is often needed for a definitive diagnosis.

Treatment overview

Treatment may involve topical or systemic therapy, depending on the type and distribution of lesions. It is possible for some dogs to spontaneously resolve mild disease, but most dogs will need medical intervention.1,3

Topical therapies may include clipping the coat and using lime sulfur dips or miconazole shampoos. Systemic therapy is most often used with generalized infections, and the most commonly used medications are griseofulvin and azole antifungals (e.g. itraconazole, ketoconazole).1,3 Because dermatophytosis lesions can be pruritic, bacterial infections secondary to self-trauma are common and may require antibiotic therapy. Treating dermatophytosis-associatedpruritus with corticosteroids is contraindicated.1,3

To deter the spread of infection to other animals and people in the household, isolation of the affected animal and environmental decontamination of bedding and other potential fomites may be necessary.1-3

This case report was provided by Maria Vandis, DVM, and Joyce S. Knoll, VMD, PhD, DACVP, Department of Biomedical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

REFERENCES

1. DeBoer DJ, Moriello KA. Cutaneous fungal infections. In: Greene CE, ed. Infectious diseases of the dog and cat. 3rd ed. St. Louis, Mo: Saunders/Elsevier, 2006;530-538.

2. Gross TL, Ihrke PJ, Walder EJ. Diseases of the hair follicles. Veterinary dermatopathology: a macroscopic and microscopic evaluation of canine and feline skin diseases. St. Louis, Mo: Mosby-Year Book, 1992;243-244.

3. Scott DW, Miller WH, Griffin CE. Fungal skin diseases. Muller and Kirk's small animal dermatology. 6th ed. Philadelphia, Pa: WB Saunders, 2001;339-357.

4. Noli C. Practical laboratory methods for the diagnosis of dermatologic diseases. In: Bonagura JD, ed. Kirk's current veterinary therapy XIII. Philadelphia, Pa: WB Saunders, 2000;528-530.


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