Thursday, February 10, 2011

What We Tell Our Clients When their Cat is Diagnosed with Ringworm


Despite the name, ringworm is not a “worm”.  It is a fungal infection (dermatophytosis) of the hair and skin.  It is also one of the few feline infectious diseases that can be transmitted from cats to humans. 

Cats may become infected with ringworm if exposed to infective spores. The most common sources of ringworm spores are an infected animal, a contaminated object, or a contaminated environment.  Once the spores land on a cat’s fur, if they survive the cat’s natural defense mechanisms (for example, grooming and sunbathing), they adhere to and invade the hair shaft and skin, initiating the infection.

            Cats of any age, sex, or breed are susceptible to infection.  Kittens in general are the most susceptible population, with the head, face, ears, and forelimbs primarily involved.

            Although ringworm can have a variety of appearances, the classic look of ringworm includes one or more areas of patchy hair loss with mild or moderate crusting or scaling.  A definite diagnosis is made via fungal culture, where hairs are taken from affected areas and placed on a special fungal culture medium. Shining a fluorescent light, called a Woods Lamp, on the hair coat may help better identify infected hairs, for better sampling for the fungal culture.  The culture medium contains a color indicator that turns the medium red when ringworm starts to grow on it.  It takes 4 or 5 days for the fungus to grow.   If the culture medium turns red in 4 or 5 days, it is considered a positive test for ringworm. If a cat tests positive, a fungal culture should be performed on all other animals in the household.

Cats that test positive for ringworm need some kind of treatment.  Treatment plans may vary somewhat for each individual cat, but they all involve three basic steps – topical therapy (bathing) with some type of shampoo, oral medication, and environmental decontamination.

Topical therapy involves bathing the cat (and other animals in the household) twice weekly with an anti-fungal shampoo. For the shampoo to be effective, it is important that there be a contact time of 10 minutes with the cat’s fur.  Longhaired cats may need their coats clipped.  This removes infected hairs and minimizes continued shedding of hair fragments and spores into the environment. It also allows for more thorough penetration of the anti-fungal shampoo.  Shorthaired cats usually do not need to have their coat clipped. On days that the cat is not receiving a bath, applying an anti-fungal lotion (for example, Conofite lotion) to affected areas on the coat may be beneficial, as long as the cat doesn’t lick it right off.

            The cornerstone of treatment for ringworm is systemic therapy with an oral medication.  There are many drugs that are effective against ringworm.  Terbinafine is particularly effective, and it usually only requires two weeks of treatment.  The drug is extremely safe, although in rare instances, cats may show poor appetite and elevation of some liver parameters.  This should be monitored.

The protocol we recommend is as follows:

Initial visit:
Thorough physical exam; sample hairs for fungal culture.
Prescribe terbinafine orally, once daily, for two weeks.
(Give medication with food for maximum effectiveness.)
Bathe all animals in household with anti-fungal shampoo twice weekly for four weeks.

Four weeks later:
Sample hairs for fungal culture.
Perform a chemistry panel to check liver parameters.
If the culture is negative, continue twice weekly baths.
If culture is positive, begin a second two-week course of terbinafine in addition to bathing.

Two weeks later:
Sample hairs for fungal culture.
Two negative cultures, two weeks apart, indicate that the ringworm infection has resolved.

The third aspect of treatment is environmental control.  In any ringworm infection, infective hairs and spores are always shed in the environment.  These hairs can be a source of re-infection for the cat, and for people.  Owners of infected cats can maximize the chances of eradicating the infection by limiting environmental contamination in the home.  Here are the currently recommended environmental control measures for treating ringworm:

·        Confine all infected cats to one easily-cleaned room during the treatment period.
·        Thoroughly vacuum floors and furniture, to remove infected hairs and spores.  Throw out the vacuum cleaner bag.  Disinfect the canister with bleach if using a bagless vacuum.  (Many people like to use an inexpensive vacuum that can simply be thrown out when the ringworm episode is over).
·        Wash floors and other contact surfaces with detergent and water.
·        If possible, disinfect hard floor surfaces with a 1:10 diluted bleach solution (1½ cup bleach in 1 gallon of water).  This diluted bleach solution will kill 80% of fungal spores with one application and any surface that can be bleached, should be bleached. Ten minutes of wetting time is ideal.  Bleach will not kill spores in the presence of dirt so it is important that the surface be properly cleaned before it is bleached.
·        Dust other surfaces with Swiffer™ or other electrostatic cloths.  These are very effective at removing spores. (Throw out after each use.)
·        Launder area rugs, cat bedding, bed linens that the cat may have slept on, etc.  Use hot water, and set the dryer to the hottest setting.  Launder (or discard) pet toys, too.  Disinfect (or discard) any grooming brushes you’ve used on the cat.
·        Vacuum (and disinfect) any vehicles and cat carriers used to transport the cat.
The above cleaning measures should be performed twice weekly.  The ringworm fungus can remain infective in the environment up to 18 months, so cleaning is essential to avoid re-infection.
Because ringworm is contagious to people, you should consult with your doctor if you notice any unusual skin lesions on family members, especially after contact with animals suspected of having ringworm.  The fungus takes advantage of skin belonging to those with reduced immune capacity. This puts young animals and children, elderly people and pets, those who are HIV-positive, people on chemotherapy or taking medication after transfusion or organ transplant and highly stressed people and animals at high risk.  In general, if you do not already have ringworm at the time your pet is diagnosed, you probably will not get it.

            Ringworm is a nuisance, and treatment is labor-intensive. However, ringworm has no serious health consequences for most cats, and most cats are easily cured with no lasting negative effects.

Please feel free to ask us if you have any questions or concerns at 

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