Dermatophytosis In Dogs And Cats

Dermatophytosis (ringworm) is a fungal infection of the horny tissue that forms nail, hair and skin. It is caused by Microsporum canis, Microsporum gypseum (from soil), or Trichophyton mentagrophytes (from rodent contact) fungi that affects humans and animals. The infection animals release infective spores in the environment which will then contaminate other animals or humans. Infected animals usually develop immunity so the infection will spontaneously disappear after a few weeks to months. In cats, up to 98% of infections are caused by Microsporum canis.²

Signs

The clinical signs of Dermatophytosis may include:

• Alopecia (hair loss)
• Circular and patchy skin lesions, raised plaques on the skin
• Furunculosis on legs and paws (acute abscess of a hair follicle due to infection by Staphylococcus)
• Facial folliculitis (inflamed hair follicles)
• Nailbed and nail infection
• Irritated, scaly and itchy skin

Persian cats may develop deep furunculosis.¹ Because dermatophytes cause facial dermatitis, they frequently involve the eyelids, and typically produce a dry, crusty alopecia around the eyes. The diagnosis is established on the basis of direct microscopic examination of scrapings.⁴

Dermatophytosis in dogs reveals in different forms and can often mimic other skin diseases: eczema, dermatitis, pyoderma, dermatophilosis and mange. Diagnosis is based on clinical signs. Often additional laboratory tests are needed for a final diagnosis.

Lesions are examined with a Wood's lamp (ultraviolet light source). Microsporum canis fluoresces with greenish color. A systematic diagnostic procedure can prevent a wrong diagnosis and allow for the right treatment.

Dogs at Risk

Young dogs up to one year old and dogs with weakened immune system, having other health disorders (for example, diabetes) or infected with ringworm, are most frequently affected. In cats skin lesions are more frequent, in dogs more severe. Male dogs are most often affected. Heavily infected animals may develop skin ulcers. The hair becomes thin and broken, the skin becomes scaly and scabby. Most lesions occur on the head and neck. Yorkshire terriers And Jack Russell terriers may be predisposed to M. canis dermatophytosis.^1,3

Treatment

Treatment consists of application of different antifungal medications, rinses and shampoos: lime sulfur, enilconazole rinses, 2% miconazole/chlorhexidine shampoo, itraconazole, lufenuron and other medications. The cure may take from to 2 to 4 months. The use of disinfectants such as bleach or enilconazole has been proven effective to destroy the spores in the environment. A fungal vaccine is used for preventing this fungal infection and is administered at the time of treatment, particularly in cats.

Studies show that infected cats appear to cause substantial environmental contamination and spread Microsporum canis, contaminating house air and surfaces. Dogs seem to contaminate surfaces, but they never contaminate the air.

Since dogs and cats live more and more in contact with humans, and a lot of dogs and cats are carriers of dermatophytes, dermatophytosis is the most important risk of developing a "mange" in humans. Clipping away affected hair and burning the clippings should be performed in all cases of generalized dermatophytosis and dermatophytosis in long-haired cats to decrease environmental and human exposure. Confining the animal to easily cleaned areas is helpful.¹

References

1. Michael Schaer. Clinical Medicine of the Dog and Cat
2. By Arthur Rook, Tony Burns (FRCP.) Rook's textbook of dermatology, Volume 4.
3. Sue Paterson. Manual of skin diseases of the dog and cat
4. Kirk N. Gelatt. Essentials of veterinary ophthalmology

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