What is ringworm?
Ringworm is the common name given to a fungal infection of the skin, hair, and nails. Ringworm infections can occur in humans and in all domesticated species of animals. The name comes from the classical appearance of the round, red, raised 'ring' marking the boundary of inflammation in people infected with the disease. The common name of ringworm is somewhat misleading, in that it is not an infection caused by a worm, and the infected areas are not always ring-shaped.
The organisms that cause ringworm infections belong to a specialized group of fungi known as dermatophytes, so the medical name for this disease is dermatophytosis. Some types of dermatophytes are species-specific, meaning that they will only infect one species, whereas others can be spread between different species of animals or from animals to humans. In cats, one species of dermatophyte is responsible for almost all ringworm infections. This species is also infectious to dogs and humans.
How is ringworm transmitted?
Ringworm is contagious and transmission occurs by direct contact with the fungus. It may be passed by direct contact with an infected animal or person or by touching contaminated objects and surfaces. The fungal spores may remain dormant on combs, brushes, food bowls, furniture, bedding, carpet, or other environmental surfaces for up to 18 months. Contact with ringworm fungus does not always result in an infection. The amount of environmental contamination is an important factor in the development of a ringworm infection, as is the age of the exposed animal.
"The fungal spores may remain dormant on combs, brushes, food bowls, furniture, bedding, carpet, or other environmental surfaces for up to 18 months."
What does ringworm look like?
Ringworm can be challenging to detect in cats since the lesions of ringworm may be very mild or even undetectable. Ringworm fungi feed on the protein that makes up the outer layers of the skin, hair, and nails. A ’cigarette ash’ scaling in the depths of the coat may be the only visible indicator of ringworm infection in cats. Some cats may have round thickened patches of skin with hair loss. Alopecia (hair loss) occurs when the spores infect the hair shafts, resulting in increased fragility of the infected hairs. In cats, the main sites for these lesions are the skin on the head, chest, forelegs, and along the ridge of the back.
Occasionally, infection of the claws may occur. The claws become rough and pitted, develop a scaly base, and they may eventually become deformed.
Ringworm may sometimes cause a more generalized disease where a much larger area of the body is affected, often seen as patches of hair loss.
Some cats, especially longhaired breeds, may have ringworm without any clinical signs or hair loss and can still infect other animals or people.
"Some cats, especially longhaired breeds, may have ringworm without any clinical signs or hair loss and can still infect other animals or people."
How is a ringworm infection diagnosed?
Some cases of feline ringworm will glow with a yellow-green fluorescence when the skin and coat are examined in a dark room under a special ultraviolet lamp called a Wood's lamp. However, not all cases show clear fluorescence and some other species of dermatophytes do not fluoresce under a Wood’s lamp. Therefore, additional diagnostics may be needed to confirm that there are ringworm fungi present.
The most accurate method for diagnosing ringworm in cats is by a culture of the fungus in a laboratory. To do this, samples of hair and skin scrapings are taken from the cat. A positive culture can sometimes be confirmed within a couple of days, but in some cases, the fungal spores may be slow to grow, and culture results can take up to three weeks.
There are numerous causes of hair loss in cats. Before making a diagnosis of ringworm, your veterinarian may recommend additional testing to rule out other possible causes.
How is ringworm in cats treated?
The most common way to treat ringworm in cats is to use a combination of topical therapy (application of creams, ointments, or shampoos) and systemic oral therapy (administration of anti-fungal drugs by mouth). For treatment to be successful, all environmental contamination must also be eliminated. Ringworm cultures will be done periodically after the start of treatment to determine if your pet is still infected.
"For treatment to be successful, all environmental contamination must also be eliminated."
DO NOT stop treatment unless your veterinarian has made this recommendation. Stopping treatment too soon can result in a recurrence of the fungus.
If there is more than one pet in the household, try to separate infected from non-infected animals and just treat the infected ones. In some situations, it may be preferable to treat all pets. Your veterinarian will advise you on the best treatment given your individual circumstances.
Occasionally, topical therapy is used alone for the treatment of ringworm, but more commonly it is used in combination with oral medication. Various creams and ointments containing miconazole (Micaved®), terbinafine (Lamisil®), or clotrimazole (Otomax®, Otibiotic®) are available to apply to localized areas of the skin affected by ringworm. Often, these are aided by using a chlorhexidine + miconazole-based shampoo or a lime sulfur dip that can be used twice weekly. Topical treatment will usually be necessary for a period of several weeks to several months.
Shaving the hair in small areas may be sufficient if only one or two areas are affected. If there is a more generalized disease, or if your cat is a longhaired breed, your veterinarian may recommend clipping all of your cat’s hair. It is extremely important to only use preparations that have been specifically provided or recommended by your veterinarian.
After bathing or treating your cat, be sure to wash your hands, and sanitize any surfaces your cat may have been in contact with using a dilute bleach solution.
In most cases of ringworm, effective treatment will require the administration of an oral anti-fungal drug. The most commonly used drugs for this purpose are itraconazole (Itrafungol®, Sporanox®, Onmel®) or terbinafine. The response of individual cats to treatment varies and if therapy is stopped too soon, the disease may recur. Treatment usually lasts for a minimum of six weeks but, in some cases, much longer therapy is required.
"The response of individual cats to treatment varies and if therapy is stopped too soon, the disease may recur."
Infected hairs contain numerous microscopic fungal spores that can be shed into the environment. Infection of other animals and humans can occur, either by direct contact with an infected cat or through contact with fungal spores in a contaminated environment. In addition to minimizing direct contact with an infected cat, it is also important to keep the environment as free of spores as possible. It is worthwhile to restrict the cat to rooms of the house that are easy to clean.
Clipping the hair (with careful disposal of the hair) combined with topical antifungal treatment of affected areas of skin may help to reduce environmental contamination. Do not use scissors to remove your cat’s hair. It is important to remove pet hair from floors or furniture as it may be contaminated with fungal spores.
Environmental contamination can be minimized by thorough damp mopping or vacuuming of all rooms or areas that are accessible to your cat; this should be done daily. Fungal spores may be killed with a solution of chlorine bleach and water using the dilution of one pint of chlorine bleach (500 ml) in a gallon of water (4 liters) where it is practical to use it.
Although ringworm is a self-limiting infection in many cats with resolution typically taking three to five months, treatment of the disease is always necessary to minimize the risk of spread of infection to humans, especially children, and other pets.
How long will my cat be contagious?
Infected pets remain contagious for about three weeks if aggressive treatment is used. The ringworm will last longer and remain contagious for an extended time if only minimal measures are taken or if you are not compliant with the prescribed approach. Minimizing exposure to other dogs or cats and to your family members is recommended during this period.
Two consecutive negative fungal cultures will indicate successful treatment of your cat.
Will my cat recover from ringworm?
The majority of cats, if treated appropriately, will recover from a ringworm infection. While the appearance of the lesions may not change much during the first week or so of treatment, some improvement should be evident within two to three weeks. Symptoms may recur if the treatment is discontinued too early or is not aggressive enough (i.e., only topical treatment was used), or if your cat has an underlying disease that is compromising its immune system.
"The majority of cats, if treated appropriately, will recover from a ringworm infection."
Occasionally, despite appropriate treatment, the infection persists. In this situation, your veterinarian may have to try alternative anti-fungal drugs.
What is the risk to humans?
Ringworm can be transmitted quite easily to humans, particularly children, and it is important to take appropriate steps to minimize exposure to the fungus while the cat is being treated. Ringworm is more likely to be transmitted to and cause clinical signs in humans who have a depressed immune system. If any people in the house develop skin lesions, especially small patches of skin thickening and reddening with raised scaly edges, medical attention should be sought. Ringworm in humans generally responds very well to treatment. However, the ringworm fungus can remain infectious for up to 18 months in the environment and re-infection may occur. It is important to wear gloves when handling infected animals and wash hands thoroughly afterward.