About: Ringworm in cats is a highly contagious fungal infection of the skin and fur.
Transmission: Cats become infected by direct contact with an infected animal or via fungal spores which are in the environment.
Circular, scaly red lesions which start out small and increase in size
Areas of hair loss
Small pustules may be found in the lesion
The head, ears and tail are most commonly affected
Treatment: Oral anti-fungal drugs, medicated baths and/or medicated shampoos and dips. The environment must be cleaned at the same time as the cat is treated.
What is ringworm?
Also known as dermatophytosis (pronounced der-mato-ptosis), ringworm a common fungal infection which affects the skin, fur, and nails of cats. It is caused by a microscopic group of parasitic fungal organisms known as dermatophytes, meaning “plants that live on the skin“.
Ringworm invades the dead, outer layers of the skin, claws, and hair. The name ringworm comes from the ring like, circular lesions which develop on the cat’s skin. The fungus is more common in areas of high humidity and temperatures.
Kittens and senior cats, cats in crowded environments such as catteries and shelters are at greater risk. Persian and Himalayan cats appear to be more predisposed to the disease than other breeds which may suggest a genetic component.
Ringworm is a zoonotic disease, which can be passed on from cats to humans. Many other species of animal are also able to catch and transmit ringworm. The fungus thrives the best in warm, humid environments.
The geographical distribution of ringworm is worldwide.
Types of dermatophytes:
There are three most common types of dermatophytes which may cause ringworm:
Microsporum canis (M. canis): This species of ringworm is almost always a cat and accounts for approximately 75-98% of ringworm seen in cats.
Microsporum gypseum (M. gypseum): This species of ringworm is usually from dogs and cats who dig in contaminated soil.
Trichophyton mentagrophytes: Dogs and cats when they are exposed to rodents or their burrows.
Ringworm is extremely contagious. A cat can become infected with ringworm by the following ways:
Direct contact: With an infected animal. This may include grooming, rubbing against each other, sleeping together.
Indirect contact: Clothes, bowls, furniture and hands which have been in contact with an infected animal.
Environment, such as contaminated bedding, grooming equipment, cat carriers, carpet, furniture, air vent filters, and soil. Spores attach to the hairs, which are shed into the environment and can remain infective for up to 18 months.
Most healthy adult cats have a natural resistance to the fungus.
The symptoms of ringworm typically appear two weeks after exposure.
Up to 20 percent of cats are asymptomatic carriers. This means that they carry the fungus but show no signs of infection. Asymptomatic carriers are still able to pass ringworm on to other cats (as well as humans and dogs).
Skin and hair:
Circular patches of rough, scaly skin with a red outline and broken hairs or bald patches.
Small pustules in the area of hair loss.
Lesions are the result of an inflammatory response to the fungus and are found most often on the head, pinnae followed by the limbs and tail, however, any part of the body can be affected.
Lesions may range from small and barely noticeable to severe, affecting large parts of the body. Ringworm may or may not be pruritic (itchy).
Large areas of hair loss may occur without characteristic rings, crusts or exudate.
Severe cases of ringworm may lead to folliculitis and/or secondary infection of the skin.
Infection of the claws may present as claws which are easily broken, flaky, crusted and malformed.
Are some cats more susceptible?
Ringworm is more common in younger cats under 12 months of age and senior cats over 10 years old. Adults have had time to build up a natural immunity to the fungus, which makes them more resistant to infection. Kittens are at greater risk of infection due to their immature immune systems and possibly because they are less efficient at grooming, and thus removing the fungal spores.
Immunocompromised cats (such as those with feline immunodeficiency virus, feline leukemia virus, undergoing chemotherapy or on long-term steroids) are also more vulnerable to ringworm.
Longhaired cats are more likely to have ringworm than short-haired cats, possibly because the fungus can easily become trapped deeper within the fur.
Cats who are run down due to sickness, under-nourished, stressed and/or in crowded conditions such as animal shelters and catteries are at increased risk.
A simple way to diagnose ringworm is to use an ultraviolet Wood’s lamp (also known as a black light) on your cat, although only around 50% of ringworm strains will show up. The infected hair shafts will glow a fluorescent green when exposed to a Wood’s lamp.
Microscopic examination of hairs:
For rapid diagnosis, your veterinarian may choose to perform a microscopic examination of the hairs for microscopic fungal spores. This method has its pros and cons. Spores are difficult to see, it is best performed by an experienced mycologist (a botanist who specialises in the study of fungi). If the sample taken has no spores, diagnosis may not be accurate. A Wood’s lamp can be useful for identifying affected areas.
This is the best way to definitively diagnose ringworm. Your veterinarian may take some samples of your cat’s hair, scales or crusts from lesions with a fresh toothbrush and grow them in a lab on a special dermatophyte test medium (DTM) that enhances fungal growth. The benefit of performing a fungal culture is that the lab will be able to diagnose the exact species of fungus. It will take around ten days to perform the culture. If one cat tests positive to ringworm, test all pets in the home with a fungal culture, even those without symptoms.
Ringworm PCR panel:
This new test by Idexx uses polymerase chain reaction to identify ringworm. Hair, skin and nail samples can be used
Sometimes, if the lesions look uncharacteristic, a biopsy will be necessary.
Your veterinarian may also want to run additional tests to determine if your cat is suffering from an underlying medical condition which has made him more vulnerable to ringworm.
Once a diagnosis has been made, it will be necessary to treat both your cat and the home. If you live in a multiple cat household, all cats in your home will need to be treated. It is easier if you can keep all cats confined to just one room while treatment is underway to avoid spreading spores around the home.
Always use gloves when handling a cat with ringworm and change your clothes immediately afterward. Wash in an anti-fungal rinse (available from the laundry aisle of your supermarket) to kill any spores you may have picked up.
Carefully follow instructions—either on the medication packet and or from your veterinarian—when treating your cat. In healthy cats, ringworm will often resolve itself in two to four months.
It may be recommended that longhaired cats be shaved during treatment, this is because the fungus can become trapped in the long coat, making it harder to treat. It is not necessary to shave shorthaired cats unless the infection is widespread.
Ringworm can take several months to eliminate ringworm. Treat all cats in the home, even those without symptoms.
The treatment of choice should include both oral treatment as well as topical dips or shampoos.
This oral drug has overtaken Griseofulvin in its use to treat ringworm as it has fewer side effects. It prevents the growth of the fungus by preventing it from producing ergosterol, a component of the cell membrane, causing the contents of the fungus to leak out.
Dosage: 5 mg per/kg once per day for 7 days, stop for 7 days, repeat three times.
Side effects: Side effects are mild but may include nausea and loss of appetite.
This is the most common anti-fungal drug for use in cats. Griseofulvin inhibits fungal cell wall division by altering the structure and function of the microtubules. This allows the cat’s immune system to gain control and fight off the infection.
Systemic and topical treatments (listed below) are most effective when used concurrently.
Dosage: Administer twice a day with a fatty meal.
Precautions: Griseofulvin cannot be used in stud cats, pregnant queens, or females you plan to breed within two months of treatment, as it can cause birth defects.
Do not give griseofulvin to cats with FIV.
Pregnant women should not handle Griseofulvin.
Side effects: Nausea, fever, lethargy, diarrhea, anemia. In rare cases, Griseofulvin can cause bone marrow suppression and liver disease in cats. If your cat becomes sick, seek veterinary attention immediately.
Other drugs include:
Lime sulfur dips using an 8% concentration twice a week are the most effective. Clipping longhaired cats can increase the effectiveness of treatment and decrease environmental contamination. Do not allow the cat to lick its coat before it dries, as this can cause vomiting.
Bathe twice a week for approximately two to four weeks. Lime sulfur dips can cause yellowing of the coat; however, this will fade in time.
These are safe to use on pregnant cats and kittens over 2-3 weeks of age.
Other topical treatments include:
Accelarated hydrogen peroxide rinse (1:100)
Ketoconazole (1% or 2%) shampoo
Miconazole (1% or 2%) shampoo
Produced by Fort Dodge, the Fel-O-Vax® MC-K vaccine is for healthy cats over four months of age. This vaccine is only effective for M. canis. Administration is as follows:
16 weeks – 1st vaccination
18 weeks – 2nd vaccination
20 weeks – 3rd vaccination
Fel-O-Vax® MC-K is not available in all countries, including Australia.
Decontaminating the environment:
Vacuum daily and if possible, throw out the vacuum cleaner bag. It is important to remove all cat hair from the environment. Vacuum under furniture, in corners. If you can’t throw out the vacuum cleaner bag, or have a bagless vacuum, empty the barrel (preferably outside), and wipe it out with a bleach solution.
Disinfect surfaces: Diluted bleach (1:10, one part bleach to ten parts water) applied twice over 24 hours to clean down all surfaces including floors, walls, windows, and ledges. Note: Inorganic material inactivates bleach. Mechanical cleaning is necessary to remove dirt before you apply the bleach solution.
Steam clean: Carpets and soft furnishings. The temperature of the water should be at least 110F to kill the spores.
Discard bedding and grooming equipment: If possible, if not, wash with an antifungal disinfectant.
Vents: Vacuum and disinfect. Fill a spray bottle with a 1:10 dilution of bleach and water and apply. Discard and replace air conditioner filters.
Bleach can be aggravating to the skin and airways, use a mask, goggles, rubber gloves and keep windows open if possible.
Can I catch ringworm from my cat?
Yes, it is possible for humans to catch ringworm from cats and vice versa. Children (especially under 10 years old) or adults who are in poor health, undergoing chemotherapy or have a weakened immune system, such as those with HIV, are more likely to become infected than healthy adults. Keep affected cats/children apart to avoid spreading the fungus.
It is also possible to pass on ringworm from humans to cats.
Treating ringworm in people:
If you (or anybody in your household has ringworm), treatment with a suitable antifungal ointment or cream is necessary. Apply 2-3 times a day to the affected area(s) for several weeks. Cover ringworm lesions with a plaster/band-aid to avoid spreading the infection to other people and pets.
Wash bedding and towels regularly using an antifungal rinse and do not share towels with a person infected with ringworm.
A final note:
Ringworm can be an incredibly frustrating infection to get rid of. Please remember that in most cases it is not life-threatening. Avoidance is always better than cure, particularly with ringworm. Ways to reduce the chances of your cats catching ringworm include:
Isolate new cats for two weeks, not only to see if ringworm rears its head but also other contagious diseases. Bear in mind though that even if you have taken precautions, cats can be carriers. The photo above is my own daughter who developed ringworm around the same time we adopted a new kitten. He had no sign of ringworm himself but was a likely source. None of my other cats caught ringworm, sadly the kitten died shortly after his adoption from an unrelated condition.