Canine nodular dermatophytosis

In companion animals, dermatophytosis as a common zoonotic disease, is a skin disease caused by a superficial fungal infection of keratinized skin structures by zoophilic, geophilic or anthropophilic fungal organisms of three anamorphic genders namely, Microsporum, Epidermophyton and Trichophyton, none of which form part of the cutaneous flora. Although they all develop in the stratum corneum of mammalian skin (in the outermost layer of skin and in the hair follicles), the epidemiology, pathogenesis and clinical consequences of infection significantly vary in pets.

With their zoonotic potentials, pet owners become so concerned with a severe inflammatory skin disease. Although, it is not a life-threatening disease, but it is very contagious and does require the intervention of a veterinarian. The infected area does not itch, but the affected hair follicles are brittle and break easily, which helps spread the disease throughout the body and kennel. In some cases the fungus infects the claws, making them brittle and rough.

Case study

A 3-year-old male German Shepherd dog was presented to the clinic with a massive alopecia and blister-like lesions on the abdomen, and remarkably patches of hair-loss with perfurative lesions on the forelimb, back and flanks, as the chief complaint. They had appeared over two weeks ago and since then, the dog has been licking it all the time to the extent that the owner had to put him on a elizabethan collar.  

Deep skin scraping of the alopecic area was performed for evaluation. No mites species such as Demodex and/or Sarcoptes, were found on microscopic examination of samples.

Few samples from the blister-like lesions on the abdomen were obtained by fine-needle aspiration. A few smears were made on the microscopic slides which were then stained with Wright's-Giemsa. Cytologic examination revealed moderate numbers of erythrocytes, inflammatory cells with nondegenerate neutrophils, activated macrophages as well as a few small lymphocytes and eosinophils. Some tissue samples were obtained by touch-smear and stained with Wright's-Giemsa. Study showed squamous epithelial cells, RBC, netrophils and multiple cocci bacteria. Also fragmented fungal hyphae and small, solitary, irregularly shaped structure

Based on cytologic examination of the lesions, the presumptive diagnosis was mixed inflammation secondary to infection with a nonpigmented fungus. Differential diagnoses for mycotic infections that form hyphal elements in tissues include dermatophytosis (e.g. Microsporum species, Trichophyton mentagrophytes) and infection with Aspergillus or Penicillium species.

Hair samples were collected using the brush technique. The specimens were placed in a package and transported to the laboratory for dermatophyte culture. Fungal cultures were performed by pressing the bristles of the brush onto 90 mm Petri dishes containing Sabouraud agar with chloramphenicol (0.5%) and actidione (0.4%) (Liofilchem Diagnostici?, Roseto degli Abruzzi, Italy) and incubated at 25°C for 15 days. Colonies grown in the medium were identified to species based on their morphology and microscopic characteristic of the hyphae, macroconidia and microconidia as described previously. Microsporum canis was the isolated species.

The main reservoir for Microsporum canis are cats and dogs; however, it can also be transmitted to humans through direct and indirect contact with animals and fomites such as combs, brushes, hats, furniture, linens etc. The greatest risk factor for acquiring infection is contact with damaged cells on skin, hair and nails. It should be noted that Microsporum canis can infect all mammals.

Treatment of ringworm depends on the severity of the infection. A veterinarian may prescribe oral medications alone or with a medicated shampoo, ointment or a dip to kill the fungus. Systemic antifungal therapy targets the active site of fungal infection and proliferation on the infected animal. Unless the infection is eliminated, the infected animal is at risk for further spread of lesions on its body, continued seeding of the hair coat with infective spores, and being a source of infection for other animals and people.

The most commonly used systemic antifungal drugs for dermatophytosis in veterinary medicine are itraconazole, ketoconazole, terbinafine and griseofulvin. In our case, the treatment was initiated with oral Ketoconazole 200mg (10mg/kg PO OID) and  twice weekly application of lime sulfur. An antibiotic such as Co-Amoxiclave 625mg (20mg/kg PO BID) was also considered. After a month of therapy, spray of lime sulfur was discontinued and instead, Ketoconazol shampoo was prescribed to apply on weekly basis. The lesions were gradually disappeared and over a month, the hair coat started to grow.

Six months later, 

References:

Rebell G, Taplin D. Dermatophytes. Their Recognition and Identification. Coral Gables, FL: University of Miami, 1974.D

De Hoog GS, Guarro J, Gene J et al. Atlas of Clinical Fungi, 2nd edn. Utrecht, The Netherlands: Centraalbureau voor Schimmelcultures, 2000.