Wood’s lamp examination is a useful technique. About 50% of
M. canis strains produce metabolites following hair invasion
which fluoresce an apple-green colour when illuminated by the lamp.
Such hairs are excellent specimens for microscopy and culture.
Click to zoom
A plucked hair from a cat with M. canis
dermatophytosis
Note the fuzzy outline caused by a sheath of tiny spores
Wood’s lamp examination should be performed
routinely when dermatophytosis is suspected. However, not all
M. canis strains and none of the Trichophyton spp.
of veterinary importance produce fluorescence; thus, absence of
fluorescence does not discount a diagnosis of dermatophytosis.
Take care to avoid being distracted by fluorescing scales and
debris which are of no diagnostic significance; it is hair fluorescence
which is relevant.
