Dog Owner's Home Veterinary Handbook.pdf - Mr. Walnuts

152 •DOG OWNER’S HOME VETERINARY HANDBOOK
Ringworm on the muzzle
of a Cocker Spaniel.
Ringworm is transmitted by spores in the soil and by contact with the
infected hair of dogs and cats, typically found on carpets, brushes, combs, toys,
and furniture. Humans can acquire ringworm from pets, and vice versa.
Children are especially susceptible.
Ringworm takes its name from its classic appearance: a spreading circle of
hair loss with scaly skin at the center and a red ring at the periphery. Note,
however, that many cases of circular hair loss thought to be ringworm are
actually localized demodectic mange or hair follicle infection. Black fly bites
in the groin area in the spring will also have this ringed appearance. Atypical
ringworm is common, with irregular areas of hair loss associated with scaling
and crusting.
Ringworm by itself is not an itchy skin condition, but secondary bacterial
infection with scabs and crusts can provoke licking and scratching. Ringworm
can invade the nails. This results in nails that are dry, cracked, brittle, and
deformed.
A kerion is a round, raised, nodular lesion that results from a ringworm
fungus in combination with a bacterial infection that invades the roots of the
hair. In most cases the fungus is Microsporun gypseum and the bacteria is a type
of Staphylococcus. Kerions occur on the face and limbs. Therapy involves
treating the bacterial component, as described in Folliculitis (page 158).
Ringworm mimics many other skin diseases, so an accurate diagnosis is
essential. Hair infected by Microsporum canis may fluoresce green under an
ultraviolet light (called a Wood’s light), but false positive and false negative
results are common. Ultraviolet light is used as a screening tool only.
Microscopic examination of hairs plucked from areas that fluoresce can
sometimes provide an immediate diagnosis, but the most reliable method of