What is ringworm?
Ringworm is the most common fungal skin infection seen in cats. Contrary to the name, ringworm 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.
Are there different types of dermatophytes?
Yes, there are. In cats, there are three most common types of dermatophytes which may cause ringworm:
- Microsporum gypseum (M. gypseum): This species of ringworm is usually from dogs and cats that dig into contaminated soil.
- 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. *
- Trichophyton mentagrophytes: This species infects dogs and cats when they are exposed to rodents or the borrows they live in.
Microsporum canis is the most common form of ringworm in cats. It is believed that 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). This may be due to the fact that their immune systems haven't matured fully. Immunocompromised cats (such as those with FIV) are more vulnerable to ringworm. Longhaired cats are more likely to have ringworm than shorthaired cats, as are cats under stress.
Is ringworm contagious?
Yes. Microsporum canis, in particular, is highly infectious. It can be passed from cat to cat, dog to cat, cat to dog, cat to human, human to cat, etc.
How does a cat become infected with ringworm?
A cat can become infected with ringworm either by direct exposure with an infected animal or via the environment, such as contaminated bedding, grooming equipment, carpet, and furniture. The spores are attached to the hairs, which are shed into the environment and can remain infective for up to thirteen months.
How do I know if my cat has ringworm?
The most recognisable sign your cat is infected with ringworm is the presence of circular patches of hair loss, especially around the head and limbs (although it can occur on other parts of the body). other signs are grey, patchy areas of baldness, with or without redness and itching; seborrhea sicca (a type of dandruff); dry/flaky skin; and onychomycosis (infection of the claw and claw bed)
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.
- Culture: 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.
- Biopsy: Sometimes, if the lesions look uncharacteristic, a biopsy will be performed.
What are the treatments for 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. 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.
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.
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.
Dosage: It comes in tablet form to be given orally. Griseofulvin has to be taken 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®), Itraconazole, Terbinafine (Lamisil®). Speak to your veterinarian for further information.
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.
Decontaminating the environment: Vacuum daily and, where possible, throw out the vacuum cleaner bag. Diluted bleach (one part bleach to ten parts water) may be used to clean down surfaces, grooming equipment, etc. Carpets and soft furnishings should be steam cleaned. Bedding and kennels will also need to be disinfected.
Can I catch ringworm from my cat?
Yes, it is possible for humans to catch ringworm from cats and vice versa. Below is a photo of ringworm.
Written by Julia Wilson
Feline Husbandry of the Multi Cat Household (Niels C. Pederson)