When checking animals for dermatophytosis (ringworm) we often will examine them under a special type of ultraviolet light called a Wood’s lamp. 50% of strains of Microsporum canis, the most common cause of ringworm in cats, will show the infected hairs fluoresce apple green under this lamp. We still have to rely on fungal culture to confirm the diagnosis, but the lamp does have its place in checking animals which are known to be infected with a fluorescing strain and we can start treatment immediately if a case is positive as it may take up to 2-3 weeks to rule out a suspected case based on fungal culture. Here is a rather blurred photo of a cat infected with Microsporum canis showing the brigh t appe green fluorescence of the infected hairs.
To function properly the lamp has to warm up over 5 minutes and examination has to take place in a darkened room.