Ringworm in Cats

Ringworm is the common name for dermatophytosis, which is a highly contagious fungal infection that affects the skin, usually in close proximity to hair and nails. In many cases, dermatophytosis presents as a red ring-shaped infection on the outer layers of the skin. Ringworm is not life-threatening, but it can be uncomfortable and may be spread to other pets and humans. While cats of all ages can contract a ringworm infection, kittens are the most susceptible.

In some cases, ringworm symptoms are easily observed. However, in less obvious cases, ringworm can be more difficult to diagnose in cats, especially long-haired cats. The following symptoms will often cause a veterinarian to suspect ringworm. 

• Scaling of skin and coat
• Erythema, an inflamed redness of the skin
• Round thickened patches of skin
• Patchy hair loss, often accompanied by “crusty” skin
• Onychomycosis, an infection of the cat’s claws that causes them to become scaly and rough

It should also be noted that after coming in contact with ringworm fungi, some cats become carriers but never exhibit any outward symptoms. These cats will likely infect other animals and humans if they are not treated.

Ringworm is caused by a fungal infection that settles into the outer layers of the skin, usually near hair and nails. The vast majority of ringworm cases are caused by the spores of the Microsporum canis fungus, but on rare occasions, ringworm has been found to be caused by the spores of three other fungi: Microsporum persicolor, Trichophyton mentagrophytes, and Microsporum gypseum Regardless of the particular fungus that has caused the infection, the overall causes are the same.

• These fungi are highly contagious, spreading either by direct contact between animals, between animals and humans, or through contact with a contaminated object or surface. 
• Cracked skin is exceptionally vulnerable to ringworm infections, as the spores can settle within the cracks.  
• Once the skin comes in contact with the fungus, there is typically a seven to fourteen day incubation period before the infection becomes visible on the skin’s surface.

Your veterinarian will begin by conducting a thorough physical examination of your cat, looking for bald spots and inflamed or crusted skin. Your vet may also darken the room and shine a Wood’s lamp, commonly called a black light, over your cat’s skin and fur. In many cases, if the ringworm is the result of the Microsporum canis fungus, the infection will glow under the black light. Not all cases of ringworm, however, will appear under the black light. If the vet finds visual evidence of a ringworm infection, the vet may take cultures of the skin and fur in those areas to be tested for fungal spores. Although some veterinarians may feel confident in diagnosing ringworm based on visual evidence alone, especially in kittens, a culture that tests positive for fungal spores is the only definitive way to diagnose dermatophytosis. If the cat is known to have been in contact with infected animals or humans but does not exhibit any physical evidence of dermatophytosis, the vet may use a brush or comb to gather hair and skin to be tested for fungal spores.

In most cases, if left untreated, ringworm will eventually resolve itself in 90-150 days. However, ringworm should not be left untreated, the infection can be spread to other animals and humans during that period. After a diagnosis of ringworm, it is likely that your veterinarian will prescribe a three-pronged approach to treatment, which will likely last for several weeks to several months. It is imperative to follow your vet’s instructions for how often and for how long you should treat your cat’s ringworm, as early cessation of treatment will usually result in a recurrence of symptoms. Your vet will likely schedule your cat for follow-up visits so that additional cultures can be collected to measure the progress of treatment toward eliminating the infectious fungi. The three approaches to treatment are:

Topical Treatments 

• Clotrimazole ointment
• Miconazole lotion
• Shampoo containing Ketoconazole 1.0% and Chlorhexidine Gluconate 2.0%
• Shampoo containing Miconazole Nitrate 2%, Chlorhexidine Gluconate 2%

Oral Medications

• Griseofulvin
• Itraconazole
• Terbinafine

Cleaning and Sterilizing the Cat’s Environment

This is extremely important because Microsporum canis fungi have been found to remain infectious for up to 18 months.

• Careful disposal of loose fur
• Frequent mopping and vacuuming 
• Sterilizing contaminated objects and surfaces with a 1:10 ratio of bleach and water. 

Treated cats will usually begin to improve within two to four weeks, although for full recovery to take place the treatments must be administered for as long a period as your veterinarian has instructed. After the treatments begin to work, the skin will usually clear up and the hair will often begin to regrow. In environments such as animal shelters, especially kitten rescues, it can be very difficult to completely rid the environment and feline population of fungal spores. In these environments, and with cats that have shown a susceptibility to repeated infection, pet owners and shelter workers will need to be intentional about keeping the environment sterile, washing their hands and clothes often, and routinely checking the cat(s) for signs of ringworm infection. Most treated cats that live in a typical home environment will make a full recovery.