Ringworm in Cats

What Is Ringworm in Cats?

Ringworms or ringworm are the common names for dermatophytosis, a fungal infection that can affect a cat’s skin, hair, and nails. The fungus, which feeds on dead cells, is not actually a worm—the name originated from the classic round red target-shaped lesion surrounded by a scaly ring mostly seen in humans with ringworm. In cats, you’re more likely to notice hair loss and scaly lesions of any shape. 

There are several types of fungus that can cause ringworm: 

• Some are species-specific, meaning they only infect one type of animal. 

• Others can be contagious between different species, which means they can move from pets to humans. These are called zoonotic. 

• One species of dermatophyte, Microsporum canis, is responsible for almost all ringworm infections in cats. It is also infectious to humans and dogs. 

• In some cases, ringworm infections in cats can be caused by Trichophyton mentagrophytes. This species is also contagious to humans. 

Symptoms of Ringworm in Cats

The following symptoms are most commonly seen with ringworm in cats. 

• Cats may have circular thickened patches of skin with hair loss. Hair loss occurs when the fungi infect the hair shaft, resulting in weakening of the infected hairs. These hairs are easy to remove with gentle pressure. 

• Redness or gray scaling of the lesions may also be noted, along with dull, poor fur. 

• Lesions are most likely to be found on the skin on your cat’s head, chest, front legs, and spine. These lesions are usually not itchy at first but can become itchy if severe scaling or bacterial infection occurs. 

• Infection of the nails is occasionally a symptom. Your cat’s nails may become rough and have a scaly base. This can lead to distortion of the nails as they grow. 

Ringworm may sometimes cause a more generalized condition where a larger area of the body is affected, often appearing as patchy hair loss. In some more severe cases of ringworm, the skin lesions are raised and nodular. These are called granulomas. These skin lesions may frequently ooze. 

Many cats, especially longhaired breeds, may have ringworm without any clinical signs at all. These cats, called asymptomatic carriers, may still infect other pets or humans. It’s important to note that even though these cats don’t look sick, they are very contagious. 

Causes of Ringworm in Cats

Ringworm transmission occurs through direct contact with the fungus. It may be passed by direct contact with an infected animal or person, the soil, or a contaminated surface. The fungal spore is very hardy and can survive and remain dormant on bedding, carpet, furniture, brushes, and/or other surfaces for up to 18 months. Direct contact with a fungal spore causes infection, but the skin must already be open, through a scrap or scratch, in order to infect. The fungus cannot infect healthy, intact skin. 

Predisposing factors for ringworm infection include: 

• Age: Kittens and geriatric cats with compromised immune systems are at a higher risk for infection. 

• Lifestyle: Free-roaming or outdoor animals are more likely to encounter fungal spores from the environment. 

• Climate: Cats that live in warmer, more humid climates have a higher infection rate. 

• Care: Cats who live in a densely populated environment (such as an animal shelter) or receive poor nutrition are at a higher risk for infection due to the contagious and resistant nature of this fungus. 

• Health: Immune suppression (factors that decrease the ability to develop a normal immune response) can increase the risk of ringworm infection, but this is seen more in humans than in cats.   

The period of time between exposure to the fungus and the development of lesions is usually between 7 to 14 days, though with some cases, 3 to 4 weeks may pass before signs are noted. 

How Vets Diagnose Ringworm in Cats

There are several tests that can be performed to help diagnoses ringworm in cats: 

• Wood’s light: This is a fluorescent lamp. Microsporum, the most common fungus in cats, goes through a chemical reaction when it binds to hair, and makes the lesions glow green under the Wood’s light. A disadvantage of this test is that not all ringworm lesions can be seen under the Wood’s light. Further testing is often recommended and necessary. 

• Microscopic examination: Hairs taken from the edge of lesions can be examined under the microscope to search for spores. Spores are very small and can be difficult to see, so further testing is often recommended. 

• Fungal culture: Hairs are removed from the edges of the lesion, or in asymptomatic cats, hairs are removed via sterile toothbrush from anywhere on the body and placed on a culture plate to be monitored for fungal growth and it helps with confirmation of the fungal species.  
  
  A fungal culture can help determine the source of infection and allow for better cleaning of the cat’s environment. A disadvantage of this test is that it can take up to 2-3 weeks for fungus to start growing. An advantage to this test is that asymptomatic carrier cats can be diagnosed. 

• PCR testing: PCR tests are performed on hairs, looking for fungal DNA. It is faster than a fungal culture (usually results return in 1-3 days) and can confirm infection as well as the species of fungus involved. Because it checks only for fungal DNA and not for living fungus, a disadvantage is that it’s not helpful once treatment has started. Although the fungus is dead and no longer harmful, the DNA is still present so the test will remain positive. This is the best test to detect ringworm in an untreated cat. Fungal culture is best for determining when treatment can be stopped. 

• Skin biopsy: Sometimes, a biopsy is performed to find fungal spores and rule out other skin issues. 

Treatment for Ringworm in Cats

Treatment is usually a combination of medication applied to the cat’s skin and an oral medication. It’s critical to clean your cat’s environment at home to reduce further spread and lower the risk of reinfection. 

Topical therapy: Treatment that’s applied directly to the skin can be used alone when there are small lesions, but it is usually used in combination with oral medication. Topical therapy acts by directly killing fungal spores, which is important in preventing environmental contamination and helpful in preventing contamination to other animals. Topical treatment will usually continue for several weeks or even months depending on your cat’s diagnosis. 

Topicals include: 

• Creams (miconazole/clotrimazole) 

• Ointments 

• Shampoos 

• Dips (lime sulfur) 

Oral therapy: These medications are considered the most effective treatment against ringworm in cats because this treatment targets the fungus to stop reproduction and spread. Once treated, only the original fungus remains and can be removed with other treatment options. Each of these oral medications help treat the most common type of ringworm in cats, Microsporum. This same fungus is left as spores in the environment which is why environmental disinfection is so important.    

Your veterinarian may prescribe one of the following: 

• Itraconazole 

• Terbinafine 

• Griseofulvin 

Side-effects are possible when using antifungals and should be considered prior to starting therapy. Individual cats may have different reactions, but if therapy is discontinued too soon, the infection may recur. Treatment lasts for a minimum of 4 to 6 weeks, and in some cases, several months of therapy is required. Ringworm cultures are performed after the start of treatment to determine if the infection is still present. Treatment is typically continued until two consecutive negative ringworm cultures are obtained, usually 2 to 4 weeks apart. 

Disinfecting the environment: Infected cat hairs containing microscopic spores may have been shed around your home. Infection of other animals and humans, or reinfection of the afflicted cat, can occur from contact with the contaminated environment. Ways to disinfect the environment include: 

• Keeping the area as free of spores as possible 

• Clipping hair and applying topical treatment to skin lesions 

• Removing pet hair from floors and furniture  

• Use of environmental disinfectants to keep affected rooms clean and maintain a thorough cleaning schedule to ensure re-contamination or spread doesn’t occur 

Management of Ringworm in Cats

Commitment is the key to success in freeing your cat from ringworm. Infected animals shed spores into the environment, so disinfection of the areas where your cat spends time is as important as treating your actual cat. Ideally, all pets in contact with the affected cat should be tested and isolated until they are found to be clear of infection. 

Cats with ringworm will be contagious for about 3 weeks—if aggressive treatment is used. Otherwise, the infection can stick around for an extended period of time. The infection can linger for 3-6 months or even longer. Keeping your infected cat away from other animals, objects, surfaces, and family members is recommended during this time. Be sure to wear gloves when handling your cat and wash your hands thoroughly afterward. 

Most cats who get appropriate treatment will recover from a ringworm infection, and you should see improvement within 2 to 3 weeks. Symptoms may reoccur if the treatment is discontinued early or is not aggressive enough, or if there is an underlying condition affecting your cat’s immune system. If an infection persists, your veterinarian may have to try alternative medications.

Ringworm in Cats FAQs

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