What to Know About Ringworm in Cats

A ringworm is not a circular worm. It isn’t a worm at all.  It is a fungus, and it affects the skin, nails, and hair. It can affect either humans or animals when there is an irritation, or breakdown, of the skin. Dark, damp areas of the body can also harbor fungus.

Where Does Ringworm Come From?

The fungus that causes ringworm is part of a group of fungi called dermatophytes. The medical name for ringworm is dermatophytosis.  Ringworm is known as a zoonotic disease —meaning an infected cat can pass it to a human.

The fungus lives in soil. It also can live on surfaces, including the skin of humans and animals. There are around 40 different species of dermatophyte fungi. Each can cause infection to a specific type of host.

How Do Cats Get Ringworm?

Microsporum canis (M. Canis) is the cause of most of the cases of dermatophytosis — or ringworm — in cats, dogs, humans, and other species.

Ringworm causes infection by feeding on keratin, a protein found in the outer layers of the nails, skin, and hair.

Spores from the ringworm grow around infected hairs — the main source of infection for animals. They adhere to the skin, and any abrasion or damage will allow the ringworm to grow more rapidly. Young cats and long-haired cats get ringworm most often. The younger cats have less developed immune systems. Long-haired cats do not groom very efficiently — so spores are more easily trapped on skin surfaces.

Since ringworm is so contagious, cats can easily spread it to each other. The shedding of hair makes it easily spread through areas where cats interact. Direct contact can cause the spread, or items such as clippers, toys, and bedding can cause contamination. Spores can remain active for years and can be hard to kill.

Cats won’t necessarily develop an infection, however, if they come into contact with the fungus. For example:

• The cat may brush the dermatophytes/spores off in the process of grooming
• The dermatophytes may become an inactive part of the skin’s natural residence
• Stronger organisms already on the skin may cause the spores to die off
• It may provoke a small inflammatory response 

What Are the Symptoms of Ringworm in Cats?

In cats, ringworm can sometimes be hard to detect. The lesions can be mild or unnoticeable because some cats may be “asymptomatic carriers” — or have no clinical signs or hair loss. This is especially true of long-haired cats. The most common signs of ringworm in cats include:

• Broken down/bristly hair
• Crusty, scaly skin and dandruff
• Hair loss in a circular pattern
• Areas of inflamed skin
• Increased grooming and scratching
• Infection of the claws/nail bed

Skin lesions are usually circular and near the head, ears, or legs. Hair around the area may be damaged. But ringworm can look similar to other skin diseases. This includes feline acne, dermatitis, and alopecia — all of which may cause itching, inflammation, and scaling.

How Is Ringworm in Cats Diagnosed?

If the vet suspects that your cat has ringworm, they may first try to rule out other common conditions like dermatitis.

Most cases of M. Canis-caused ringworm in cats will glow when examined under ultraviolet light with a Wood’s Lamp. However, a microscopic culture of hairs in a lab is the best way to get an accurate diagnosis. It allows the specific fungus causing the infection to be identified. In some cases, the spores may grow slowly, and some cultures can take up to 4 weeks to identify.  

What Is the Treatment for Ringworm in Cats?

Ringworm treatment for cats may include topical antifungals which are applied to all infected areas. Treatment may also include systemic drugs — anti-fungal medicine given by mouth. If your cat is long-haired, your vet may have you clip all hairs and bathe your cat with medicated shampoos. Effective treatment usually takes up to 6 weeks.     

If one cat in a home has been diagnosed with ringworm, all other animals need to be examined. Many times, all cats in the household will be positive for ringworm and need to be treated.