Ringworm

Dear Dr Jody:  Our four year old outdoor cat “Halen” has recently developed a small bald spot near his lip.  He does get into some occasional fights with other cats in the neighbourhood, and so we thought it was just a battle wound, but it seems to be getting larger.  What should we do?

Skin lesions can be very frustrating to diagnose.  Because so many skin conditions can mimic each other, it is almost impossible to make a diagnosis solely on the appearance of the symptoms.  Since Halen is an outdoor cat, it will be important for your veterinarian to rule out ringworm.

The term ringworm is actually a misnomer, because ringworm is a skin infection caused by a fungus and not a worm.  Although the condition is more accurately referred to as dermatophytosis, which literally means “a plant growing on the skin”, for simplicity’s sake I will continue to refer to it as ringworm.

There are several different types of fungus that can cause skin infections.  Athlete’s foot and jock itch are two examples of familiar human fungal skin infections.  Many species of fungus are not particularly choosy with regards to which host they prefer.  Fungal infections like ringworm can easily be spread from pet to owner and back to pet again.

Because ringworm is “zoonotic”, meaning it can be transmitted from your cat to you, do not hesitate to have Halen tested for this organism.  Your veterinarian has several tests available to aid in the diagnosis.  Firstly, she may choose to use a Wood’s lamp, which is a type of black light that causes some species of ringworm to glow with a green fluorescence.  A second option is to perform a trichogram, whereby your veterinarian collects a sample of your pet’s fur and prepares it on a microscope slide.  Occasionally, the fungal spores are visible microscopically.  Because neither of these tests is exceptionally sensitive, your veterinarian may prefer to culture a sample of your pet’s fur.  In this time-consuming test, the fur is placed on a special gel medium and incubated for up to 14 days.  If the yellow gel changes colour, your veterinarian will be able to diagnose ringworm in your pet with reasonable certainty.

There are several types of medication available to treat ringworm positive cats.  These antifungal agents can be quite expensive, but it is important not to delay treatment since the condition presents a human health risk.  Because ringworm is a hardy and tenacious organism, it may take up to eight weeks of daily treatment for your pet to be ringworm free.