Ringworm is an infection caused by a fungus that grows in the dead, superficial layers of the skin, hair or nails. It has nothing to do with worms. The scientific name for ringworm is dermatophytosis, and fungi which cause the disease are called dermatophytes. There are approximately 40 different species of dermatophyte, each tending to cause infection in particular species of hosts. In the cat, the cause of more than 90 per cent of cases of ringworm is the dermatophyte Microsporum canis (M canis). This organism can also cause infection in many other species, including dogs and humans. Other dermatophytes that may occasionally cause ringworm in cats are Trichophyton mentagrophytes and M persicolor, (acquired by contact with infected wild rodents) and M gypseum, M fulvum and T terrestre (isolated from the soil).
How do cats become infected with M canis?
Ringworm is contagious. Spores are the infectious stage of dermatophytes and are produced by M canis during an infection. They are typically found in clusters around infected hairs and can only be seen using a microscope. Infected hairs are shed into the cat's environment. Cats may become infected either by direct contact with an infected animal or by exposure to a contaminated environment or object such as grooming tools, clippers or bedding. Spores in the environment are very robust and without treatment can remain infectious for up to two years. Spores attach to the skin and germinate to produce hyphae that invade skin and hair. It is not known how many spores are needed to start an infection. Self-grooming, particularly licking, may be an effective way of harmlessly removing spores from the skin and haircoat. Intact skin is very resistant to infection. Mites and lice are generally uncommon. The point being made here is that some degree of self trauma is probably required to enable fungal infection to develop and that ectoparasite infestation may be an additional predisposing factor.
How do cats become infected with M canis?
Ringworm is contagious. Spores are the infectious stage of dermatophytes and are produced by M canis during an infection. They are typically found in clusters around infected hairs and can only be seen using a microscope. Infected hairs are shed into the cat's environment. Cats may become infected either by direct contact with an infected animal or by exposure to a contaminated environment or object such as grooming tools, clippers or bedding. Spores in the environment are very robust and without treatment can remain infectious for up to two years. Spores attach to the skin and germinate to produce hyphae that invade skin and hair. It is not known how many spores are needed to start an infection. Self-grooming, particularly licking, may be an effective way of harmlessly removing spores from the skin and haircoat. Intact skin is very resistant to infection. Mites and lice are generally uncommon. The point being made here is that some degree of self trauma is probably required to enable fungal infection to develop and that ectoparasite infestation may be an additional predisposing factor.
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