Veterinary Medicine - December 2007 - (Page 772)

Clinical Exposures PEER-REVIEWED that form hyphal elements in tissues include dermatophytosis (e.g. Microsporum species, Trichophyton mentagrophytes) and infection with Aspergillus or Penicillium species or other nonpigmented fungi (e.g. Acremonium, Fusarium, Geotrichum, Paecilomyces, Pseudallescheria, and Scedosporium species). Zygomycosis (e.g. Basidiobolus and Conidiobolus species) and pythiosis were also considered because of the puppy’s geographic origin.1 HISTOLOGIC EXAMINATION AND DEFINITIVE DIAGNOSIS Soon after the preadoption examination, the puppy was neutered, and the thigh lesion was excised with wide margins for histologic examination. The histologic examination findings included a multifocal mixed inflammatory cell (primarily epithelioid macrophages and fewer neutrophils) infiltration of the dermis centered on the hair follicles. Moderate hyperplasia and hyperkeratosis were noted in the epidermis, consistent with self-trauma. Additionally, fungal arthrospores and hyphae were found within the hair shafts and within foci of inflammation (Figures 2A & 2B). Granulomatous folliculitis and furunculosis with intralesional dermatophyte 2A. Histologic examination of the thigh lesion from the puppy shows a hair shaft surrounded by numerous neutrophils and a few macrophages. Periodic acidSchiff (PAS) reaction revealed multiple dermatophytic arthrospores (500X; bar = 10 µm). 2B. A cross section of a second hair shaft from the thigh lesion stained with PAS revealing arthrospores and hyphal elements (200X). RECOVERY AND FOLLOW-UP The puppy had an uneventful recovery from surgery. No other treatment was given for the dermatophytosis. The lesions on the head resolved over several weeks without intervention. Eight months later, the puppy was in a new home and doing well. No new skin lesions had developed. DISCUSSION Dermatophytosis, also called ringworm, may be caused by several keratinophilic Most dermatophytes are not components of the normal canine fungal flora. arthrospores and hyphae were diagnosed. The fungal elements were consistent with dermatophytosis, specifically Microsporum canis infection. The nodular form of dermatophytosis was suspected, but fungal culture to confirm the genus and species of the dermatophyte was not done. fungal organisms, but the most common dermatophytes in dogs and cats are M. canis, Microsporum gypseum, and T. mentagrophytes. These dermatophytes invade the hair follicle, the hair, and, less frequently, the epidermis.1,2 The infective form, the arthrospore, is transmitted by direct contact with an in- fected animal or with fomites, which contain a hair, piece of skin, or scale of an infected animal. In addition, asymptomatic dogs can be carriers and may spread dermatophytosis to other dogs, cats, or people. Arthrospores cannot penetrate the dermis because of healthy skin’s innate fungistatic properties; however, if there is a breach in the epidermal layer, arthrospores may bond tightly to keratin and germinate within six hours of adherence.1 Wet or humid conditions may enhance an arthrospore’s ability to penetrate compromised skin and germinate.1,2 Most dermatophytes are not components of the normal canine fungal flora. Microsporum canis is well-adapted to dogs; however, unless the infected animal is very young, very old, or immunocompromised, it rarely causes inflammation or infection. Infections with M. gypseum and T. mentagrophytes tend to cause more serious dermatologic disease.1-3 Signalment Dermatophytosis is commonly diagnosed in puppies and young dogs. Localized or generalized disease may be present. Dogs younger than 1 year old have a 772 December 2007 VETERINARY MEDICINE

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Veterinary Medicine - December 2007 Contents Letters Editors' Guest Thanking Our Valued Reviewers The Veterinary Medicine Interview: Dr. Joseph Harari Clinical Exposures Idea Exchange Answers to Three Commonly Asked Questions About Lyme Disease Practical Ideas for Managing Common Internal Medicine Problems A Tip for Interpreting Leptospira Species Titers Investigating Proteinuric Kidney Disease Counseling New Puppy Owners: Normal Play vs. Aggressive Tendencies 11 Guidelines for Conservatively Treating Chronic Kidney Disease CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller Merial Insert

Veterinary Medicine - December 2007

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