Description

Ringworm is a fungal skin disease that in dogs is caused by Microsporum canis (70%), Microsporum gypseum (20%), and Trichophyton mentagrophytes (10%). Typical signs in dogs include hair loss and scaly skin.

Causes and prevention

Fungi thrive in moist, warm areas, such as locker rooms, tanning beds, swimming pools and in skin folds. The fungi may be present without any symptoms.

Advice often given to prevent ringworm includes:

• Avoidance of sharing clothing, sports equipment, towels, or sheets.
• Washing clothes in hot water with fungicidal soap after suspected exposure to ringworm.
• Avoidance of walking barefoot, instead wearing appropriate protective shoes to the beach and flip-flops in locker rooms.
• After being exposed to places where the potential of being infected is great, one should wash with an antibacterial and anti-fungal soap or one that contains tea tree oil, which contains terpinen-4-ol.
• Avoid touching pets with bald spots as they are often carriers of the fungus.

Diagnosis in pets

Ringworm in pets may often be asymptomatic, resulting in a carrier condition which either infects other pets, or shows disease only when the companion animal develops an immunosuppressive condition. Circular bare patches on the skin suggest the diagnosis but no lesion is truly specific to the fungus. Three species of fungi cause 95% of ringworm in pets. These are Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes.

Veterinarians have several tests to identify ringworm infection and identify species:

Woods Test This is a black light (ultraviolet light) with a magnifying lens. Only 50% of Microsporum canis will show up as an apple-green fluorescence on hair shafts, under the black light. The other fungi do not show. The fluorescent material is not the fungus itself (which does not fluoresce) but rather an excretory product of the fungus which sticks to hairs. Infected skin does not fluoresce.

Microscopic test The vet takes hairs from around the infected area and places them in a staining solution to view under the microscope. Fungal spores may be viewed directly on hair shafts. This technique identifies a fungal infection in about 40%-70% of the infections but cannot identify the species of dermatophyte.

Culture Test: This is the most effective but also the most time-consuming way to determine if there is ringworm on a pet. In this test, the veterinarian collects hairs from the pet, or else collects fungal spores from the pet's hair with a toothbrush, or other instrument, and inoculates fungal media for culture. These cultures can be brushed with transparent tape and then read by the vet using a microscope, or can be sent to a pathological lab. The three common types of fungi which commonly cause pet ringworm can be identified by their characteristic spores. These are different-appearing macroconidia in the two common species of Microspora, and typical microconidia in Trichophyton infections.

Identifying the species of fungi involved in pet infections can be helpful in controlling the source of infection. Microsporum canis, despite its name, occurs more commonly in domestic cats, and 98% of cat infections are with this organism. It can also infect dogs and humans, however. Trichophyton mentagrophytes has a major reservoir in rodents, but can also infect pet rabbits, dogs and horses. Microsporum gypseum is a soil organism and is often contracted from gardens and other such places. Besides humans, it may infects rodents, dogs, cats, horses, cattle, and swine.

Treatment in humans

Antifungal treatments include topical agents such as Miconazole, Terbinafine, Clotrimazole, Ketoconazole, or Tolnaftate applied twice daily until symptoms resolve - usually within one or two weeks.  Topical treatments should then be continued for a further 7 days after resolution of visible symptoms to prevent recurrence.  The total duration of treatment is therefore generally two weeks, but may be as long as three.

In more severe cases or where there is scalp ringworm, systemic treatment with oral medications may be given.

To prevent spreading the infection, lesions should not be touched, and good hygiene maintained with washing of hands and the body.

Treatment in pets

Treatment in pets requires both systemic oral treatment with most of the same drugs used in humans Terbinafine, Fluconazole, or Itraconazole, plus topical "dip" therapy.

Because of longer hair shafts in pets, the area of infection and possibly all longer hair of the pet must be clipped to decrease the load of fungal spores clinging to the pet's hair. However, close shaving is usually not done because nicking the skin facilitates further skin infection.

Twice-weekly bathing of the pet with diluted lime sulfur dip solution is effective at eradicating fungal spores. This must continue for 3 to 8 weeks.

Washing of household hard surfaces with 1:10 household hypochlorite bleach solution is effective in killing spores.

Pet hair must be rigorously removed from all household surfaces, and then the vacuum cleaner bag (and often the vacuum cleaner itself) discarded when this has been done repeatedly. Removal of all hair is important since spores may survive 12 months or even as long as two years on hair clinging to surfaces.

Wikipedia and GNU

The content of this entry is from the Wikipedia article "Ringworm" licensed under the GNU Free Documentation License.