What is ringworm?
Also known as 'dermatophytosis' (pronounced der-mato-ptosis), ringworm is the most common fungal skin infection seen in cats. It is caused by a microscopic group of parasitic, fungal organisms known as dermatophytes (which means "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 lesions which develop on the cat's skin. The fungus is more common in areas of high humidity and temperatures. Ringworm is seen more often in young cats and in crowded conditions such as catteries and shelters, Persian and Himalayan cats appear to be more predisposed to the disease than other breeds which may suggest a genetic component.
|Severe ringworm on Devon Rex cat (click to enlarge).||Severe ringworm on Devon Rex cat (click to enlarge).|
Ringworm is found 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): The source of 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: This species infects dogs and cats when they are exposed to rodents or their burrows.
How does a cat become infected with ringworm?
Ringworm is extremely contagious. A cat can become infected with ringworm either by direct contact with an infected animal or via the environment, such as contaminated bedding, grooming equipment, carpet, furniture and soil. The spores are attached to the hairs, which are shed into the environment and can remain infective for up to 18 months.
What are the symptoms of ringworm in cats?
Symptoms typically appear two weeks after exposure.
The most recognisable sign your cat is infected with ringworm is the presence circular patches of rough, scaly skin with a red outline and broken hairs or bald patches. It is found most often on the head 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. These lesions do not appear to be pruritic in most cats, although some may be somewhat itchy.
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% of cats are asymptomatic carriers. This means that they carry the fungus but show no signs of infection.
Are certain cats more susceptible than others?
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 FIV, 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. As has been stated above, Persian and Himalayan cats appear to be more predisposed to developing ringworm.
Cats who are run down due to sickness or who are under-nourished, stressed and/or in crowded conditions such as animal shelters and catteries are at greater risk.
How is ringworm diagnosed?
- 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: For rapid diagnosis, your veterinarian may choose to perform a microscopic examination of the hairs for microscopic fungal pores. This method has its pros and cons. Spores are often difficult to see, so 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.
- Fungal Culture: This is the best way to definitively diagnose ringworm. Your veterinarian may take some samples of your cat's hair from the infected region and grow them in a lab on a special culture 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.
- Biopsy: Sometimes, if the lesions look uncharacteristic, a biopsy will be performed.
What are the treatments for ringworm in cats?
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.
This 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: 10 mg per/kg once per day.
Side effects: Side effects are mild but may include nausea and loss of appetite.
This is the most commonly used anti-fungal drug and the only anti-fungal 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 run concurrently.
Dosage: Griseofulvin comes in tablet form to be given orally. It is administered twice a day, with food, and it is preferable to feed 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 which may be used to treat ringworm include: Ketoconazole (Nizoral®) and Terbinafine (Lamisil®). Speak to your veterinarian for further information.
Lime sulfur dips are the most effective. Sometimes, clipping the cat (especially longhaired cats) is recommended to increase the effectiveness of treatment and also decrease environmental contamination. The cat must not be allowed to lick its coat before it dries, as this can cause vomiting. Bathing should be done every four to six days for approximately two to four weeks. Lime sulfur dips can cause yellowing of the coat; however, this will fade in time.
Ringworm Vaccine: There is a ringworm vaccine made by Fort Dodge called Fel-O-Vax® MC-K. This vaccine must be given to healthy cats over four months of age and is a course of three injections. This vaccine is only effective for M. canis. After an initial dose is administered, a second dose is given twelve to sixteen days later. A third dose is given twenty-six to thirty days after the second dose. Fel-O-Vax® MC-K is not available in all countries (Australia included), please check with your veterinarian on availability where you live.
Any concurrent skin disorders such as folliculitis or skin infection will will need to be treated with antibiotics.
Decontaminating the environment:
Vacuum daily and if possible, throw out the vacuum cleaner bag.
Diluted bleach (1:10, one part bleach to ten parts water) may be used to clean down surfaces, floors, grooming equipment, etc. Carpets and soft furnishings should be steam cleaned. Bedding and kennels will also need to be disinfected. Repeat every week.
All grooming equipment should also be cleaned with a diluted bleach solution.
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.
How is ringworm in humans treated?
If you (or anybody in your household has ringworm), treatment with a suitable antifungal ointment or cream is necessary. This is usually applied 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.
Bedding and towels should be washed regularly (using an antifungal rinse) and do not share towels with a person infected with ringworm.