|What is ringworm? How do cats become infected? What are the symptoms of ringworm? How is it diagnosed? How is it treated? Can I catch ringworm from my cat?|
Ringworm at a glance
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.
Are there different types of dermatophytes?
Yes, there are. In cats, 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: Clothing, bedding 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.
- Skin and hair: The most recognisable sign that a cat is infected with ringworm is the presence circular patches of rough, scaly skin with a red outline and broken hairs or bald patches, small pustules may be located within 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.
- Claws: Infection of the claws may present as claws which are easily broken, flaky, crusted and malformed.
- Severe cases of ringworm may lead to folliculitis and/or secondary infection of the skin.
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).
- 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.
Image Nottingham Vet School, Flickr
Ringworm can not be diagnosed just by looking at the lesions as many other conditions have similar symptoms.
- Wood’s lamp: 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.
- Fungal Culture: 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, all cats (and other furred animals) in the household should also be tested with a fungal culture, even those not displaying symptoms.
- Ringworm PCR panel: This new test by Idexx uses polymerese chain reaction to identify ringworm. Hair, skin and nail samples can be used
- Biopsy: Sometimes, if the lesions look uncharacteristic, a biopsy will be performed.
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 your cat has been diagnosed with ringworm, you will have to treat both the cat and the environment. 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 afterwards. They should be washed 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. However, it is recommended that you treat your cat for ringworm to speed up the process and prevent infection of humans and other pets.
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. Shorthaired cats don’t need to be shaved unless the infection covers a large area of the body.
It can take several months to eliminate ringworm. All cats in the home should be treated, even those displaying no symptoms of ringworm.
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 commonly prescribed anti-fungal drug and drug licensed 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.
Side effects/Precautions: Griseofulvin cannot be used in stud cats, pregnant queens, or females you are planning to breed within two months of treatment, as it can cause birth defects. Side effects include nausea, fever, lethargy, diarrhoea, anaemia. In rare cases, Griseofulvin can cause bone marrow suppression and liver disease in cats. If your cat becomes sick, seek veterinary attention immediately. Griseofulvin should not be given to cats with FIV. Pregnant women should not handle Griseofulvin.
Other drugs include:
- Ketoconazole (Nizoral®)
- Terbinafine (Lamisil®)
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)
- Climbazole mousse
- Ketoconazole (1% or 2%) shampoo
- Miconazole (1% or 2%) shampoo
Produced by Fort Dodge, the Fel-O-Vax® MC-K vaccine is administered to 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: Bleach is inactivated by inorganic material such as dirt and feces, so mechanical cleaning is required to remove dirt before applying bleach.
- 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.
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.
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. The kitten showed no signs of ringworm himself, but was a likely source of the ringworm my daughter had. None of my other cats caught ringworm, sadly the kitten died shortly after his adoption from an unrelated condition.