Dermatophytosis (ringworm) is a fungal infection of the hair, superficial skin, and occasionally nails. Worms are not the problem. Three species of ringworm cause the majority of infections:
Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes.
The most common sources of infection are other infected pets, rodents, contaminated environments, and occasionally the soil. Some animals may act as carriers of the disease with no visible lesions. This is more commonly seen in cats with M. canis infections. M. canis may also live in the environment for at least 13 months, making reinfection a common problem. Infection involves more than just exposure to the fungus. Individual factors like small skin abrasions, immunity, and stress can also contribute to this disease. It most commonly occurs in dogs and cats, with highest incidences reported in kittens and puppies, immunocompromised animals, and long-haired cats. Persian cats, Yorkshire and Jack Russell Terriers appear to be predisposed.
People who come in contact with infected animals are at risk of developing ringworm. As with animals, most individuals who are exposed will not develop an infection. So the lack of infection of other animals or people in the house does NOT preclude the diagnosis of dermatophytosis.
The most common clinical signs of infection are hair loss, broken hairs, and increased pigmentation of the skin. Other signs may include red bumps, itching, crusting, scaling, and occasionally pus. When the nails are affected they can become brittle and even break. This often will result in nail deformities and loss of nails.
The diagnosis of ringworm is based on Wood’s light examination, fungal cultures, and/or skin biopsy. Cultures take up two weeks to grow. None of these tests are 100% accurate.
Therapy for ringworm includes elimination of organisms contaminating the environment, treatment of affected pets and control of inapparent carriers, which may not show symptoms.
As well as localized treatment the animal should be treated for generalized dermatophytosis.
Topical antifungal rinse or dip should be applied to the entire body one or two times per week (minimum 4-6 weeks) until follow-up fungal culture results are negative. Dogs with generalized dermatophytosis may be cured with topical therapy alone, whereas cats almost always require concurrent systemic therapy.
Effective topical antifungal solutions include the following:
- Enilconazole 0.2% solution
- Lime Sulfur 2% – 4% solution
For best results topical therapy should be combined with long term (minimum 4-6 weeks) systemic antifungal therapy and continued until 3-4 weeks beyond negative follow-up fungal culture results.
A few effective systemic antifungal drugs are available for the treatment of ringworm. Our veterinarians will recommend individualized oral therapy for your pet.
Environment and other pets
All infected animals, including asymptomatic carriers, should be identified and treated. Exposed, noninfected cats and dogs should be treated prophylactically with weekly topical antifungal rinse or dip for the duration of treatment of the infected animals. As well, the environment should be thoroughly cleaned (vacuuming is helpful but ‘Swiffer’ dusters are most effective). Household chlorine laundry bleach (5% sodium hypochlorite) diluted 1:10 in water is an effective, inexpensive environmental disinfectant.
Treatment must be continued until 1-2 consecutive negative cultures are obtained. If the infection is not totally eliminated, relapses are common.
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