From the archives of the Fanciershealth group on Yahoogroups (updated 4/28/06)

Treating feline ringworm (microsporum canis infection) can be one of the biggest health challenges that can face a cat breeder. Ringworm can be a self-limiting disease that will often “cure itself” in 4-6 months in adult, shorthaired cats with strong immune systems. However, longhaired cats, kittens, and cats with weaker immune systems usually need an aggressive approach to completely clear them of “the grungy fungi.” This is a zoonotic disease (transmittable to humans), so it should not be taken lightly by cat fanciers. Ringworm can not be successfully treated by applying topical creams or solutions to a cat. The only effective and efficient way of curing a cat or a whole cattery of ringworm is to combine the use of an oral antifungal drug with a topical treatment and to thoroughly clean the environment to prevent reinfection.

Griseofulvin (Fulvicin) is the most commonly used antifungal drug. Treatment must continue for at least 12-16 weeks. Some cats, in particular Persians, can experience a deadly form of bone marrow suppression or liver damage when treated with Fulvicin. This reaction is independent of the dose received. The dose for Fulvicin is 7 mg per pound of the microsized formulation twice a day, or 3.5 mg per pound of the ultra-microsized formulation twice a day. Fulvicin must also be given with a fatty meal to be absorbed. Fulvicin should not be used in breeding males, pregnant queens, or within less than two months of breeding a queen.

Safer and more effective antifungal drugs include itraconazole (Sporonox) at 5 mg per pound once a day, fluconazole (Diflucan) at 5 mg per pound once a day or every other day, and terbinafine (Lamisil) at 20mg per pound once a day. Mycological clearance with these drugs usually takes about half to 2/3 the time of treatment with Fulvicin. These drugs should not be used in pregnant queens, but do not affect males like Fulvicin does. No comparative, controlled studies have been performed to find out which of these three newer drugs is more effective. Ketoconazole (Nizoral) is far more toxic than any of the other drugs mentioned and should not be used in cats.

I personally recommend as an adjunct treatment, because of its extremely low toxicity and expense, the use of Program (lufenuron) at 40-50 mg per pound every two weeks. It is better to “overdose” than to underdose. All adult cats should receive one of the largest dog tablets (450 mg).  Kittens can be treated anytime over the age of eight weeks and should receive half of a large dog tablet or one complete liquid dose of the large cat size oral suspension. Treatment of kittens under eight weeks of age is off-label, but there is no reason to believe it would not be harmless. Program is safe in pregnant and nursing queens. Program is only absorbed if given with a LARGE meal, the fattier, the better. Mix the crushed tablet up with a treat your cat will gobble up and then follow it immediately with your cat’s favorite meal. For high risk catteries (and I consider ALL Persian catteries “high risk”), owners may wish to continue to dose once a month indefinitely. Although the ability of Program to prevent ringworm has been disproven in controlled studies, this drug does appear to have a slight inhibitory effect on ringworm growth. However, Program should never be used alone to try to treat a ringworm infected cat. IMPORTANT: The injectible form of Program can not be substituted for the oral form.

The only topical treatment proven to be efficacious in controlled laboratory studies is lime sulfur dips (1:32 or 1:16 dilution). Do not shave short or medium coated cats, as the skin irritation caused by the clipper blades can cause the ringworm infection to become worse. Persians, however, should be shaved with a #10 blade (not a surgical blade) because of the large volume of hair that can cause reinfection of the cat and its environment. Clipping also opens up the hairs and releases spores, but for Persian cats the advantages of clipping outweigh the disadvantages. Cats should be shaved off the premises, if possible, to prevent contaminating the environment with spores from the broken hairs. Throw away the clipper blade and immediately dip the cat in lime-sulfur afterwards. Lime-sulfur is safe in kittens, pregnant, and nursing queens. Do not allow the cat to lick itself until the dip has dried (collar if necessary). After the lime sulfur has dried, wash the nipples of nursing queens before reintroducing kittens. Dip at least once a week, twice a week is preferred.

Other shampoos have claimed to be fungicidal, but none have demonstrated efficacy by independent laboratory testing as yet. Stated efficacy against the microsporum canis fungus itself is insufficient, it is the SPORES that cause reinfection. Shampooing cats can make them worse, as the hairs break off from scrubbing and infect the surrounding skin. Dipping is better.

Once a week eniconazole dips (0.2%) have also been demonstrated to be effective to treat cats topically for ringworm, but there have been scattered reports of toxicity. Care should be taken and a Elizabethian collar used until the cat is completely dry to prevent the cat from ingesting the dip.

TREAT EVERY CAT IN THE HOUSE. Not doing so will only create a cattery with chronic carriers of ringworm and recurrent infections.

 Cleaning up the environment is the hardest part. The spores are almost unkillable, only concentrated bleach, highly carcinogenic chemicals that you don’t want in your home, and enilconazole are effective in fighting the spores. Some folks have reported success fogging with solutions such as Virkon, but the efficacy of this agent has not been confirmed by controlled laboratory studies. Bleach only works on a CLEAN surface, it does not work in the presence of organic material, so dipping cats in bleach is worthless. Treating the environment with enilconazole (Clinifarm fogger) is effective, but there may be toxicity issues with cats, so this should be used with care.

Keep in mind that the spores are carried inside of hairs, so removing all cat hair from the environment is the most important cleaning step. Discard all carpeted/fabric surfaces if possible. Bleach all surfaces (A freshly prepared solution of 1:10 bleach is recommended and should be applied multiple times). High temperature steam may also be effective. This is not the normal steam cleaning offered by your local furniture and carpet cleaner… you need HIGH TEMPERATURE steam. And vacuum, vacuum, vacuum, discarding the bag each time and spraying down the vacuum with 1:10 bleach after each use. Buy a true HEPA filtered vacuum. Blow torching metal cages is an excellent apporoach if you have the resources to do so.

The ringworm vaccine is worthless as a preventative, but may help individual cats clear their lesions faster. It is no longer marketed in the United States. Not all ringworm can be visualized with a Wood’s Lamp (“black light”). Do not rely on this as a diagnostic tool.

Other diseases CAN mimic ringworm, most notably body mites. If treatment with antifungal drugs is not working, treat with ivermectin twice, two weeks apart, and see if there is improvement. Not all ringworm looks the same. Ringworm can be completely asymptomatic or exhibit itself as a mild case of “dandruff”, skin discoloration, subcutaneous “tumors”, or large weeping lesions. Some cats are more susceptible to ringworm than others and this susceptibility can be inherited. Ringworm outbreaks can be a symptom that a cat has a weakened immune system.

How long do you treat? This is the question I get asked most often. There is only one answer: AS LONG AS IT TAKES TO ACHIEVE MYCOLOGICAL CLEARANCE. There is no “magic time” after which your cats will be cured. You can only determine whether your cats are cleared of the infection through CULTURING. The Mackensie brush technique is used to screen for ringworm. A new, sterile toothbrush is combed through the entire coat of the cat and then pressed into culture medium. Multiple cats can be cultured on one culture “slant” to help keep costs down when screening an entire cattery. Isolate cats that still culture positive from cats that culture negative. Keep treating and culturing until two cultures of the entire cattery come back negative, done at least a week or two apart. DO NOT assume a cat is “cured” simply because the lesions are gone. Cats with no lesions whatsoever can be your most potent carriers and sources of reinfection. Isolate cats as they culture negative for ringworm.

To prevent infection in the first place, culture all incoming cats before and after their quarantine period. Isolate all show cats and bath them upon returning from a cat show. But despite your best efforts, reinfection *is* common.

Ringworm has been described as “an extremely well evolved parasite of feline keratin”. It isn’t easy to avoid. The most successful warriors in this battle are the most aggressive and the most determined. DO NOT GIVE UP. Good luck!

–Lorraine Shelton