WHERE WOULD MY PET PICK UP THIS INFECTION?
The spores of dermatophyte fungi are extremely hardy in the environment; they can live for years. All it takes is skin contact with a spore to cause infection; however, the skin must be abraded as the fungus cannot infect healthy intact skin. This means that freshly shaved, scraped, or scratched skin is especially vulnerable.
Infected animals are continuously dropping spore-covered hairs as infected hairs break off into the environment. Some animals are carriers, who never show signs of skin irritation themselves but can infect others readily. A carrier might be "subclinically" infected, which means their skin is infected but shows no visible lesions. Ringworm patients undergoing treatment commonly fit in this category towards the end of their care; the skin is still dropping spores but the visible signs of infection have cleared up. A carrier can also carry the spores on their fur without being infected, much as an inanimate object might have spores on its surface incidentally. In this situation, the spores can be easily washed away. There is no obvious way to distinguish between these two types of carrier state.
There are several species of dermatophyte fungi. Different species of fungi come from different kinds of animals or even from soil thus determining the ringworm species can help determine the source of the fungal infection.
HOW DOES THE DOCTOR KNOW THIS IS REALLY RINGWORM?
In some cases, we know for sure that dermatophyte fungi are present while in other cases we are only highly suspicious. Lesions on animal skin are rarely the classic ring-shaped as in people (in fact, in animals, lesions are often not even itchy) thus some testing is usually necessary as we will describe.
Commitment is the key to success especially if you have more than one pet. Infected animals are constantly shedding spores into the environment (your house) thus disinfection is just as important as treatment of the affected pet. The infected pet will require isolation while the environment is disinfected and should not be allowed back into the "clean" area until a culture is negative. Ideally all pets should be cultured and isolated until they have been deemed clear of infection at which point they can be allowed back into the "clean" area.
Infected pets generally require oral medication which may be supplemented with topical treatment (dipping, lotion, or both). Very localized lesions might get away with topical treatment only.
ORAL MEDICATION FOR INFECTED PETS
There are primarily two medications being used to treat ringworm: Griseofulvin and Itraconazole. Both medications are relatively expensive, must be given with food, and have significant potential to cause birth defects in pregnant pets.
Treatment with either medication typically is continued for 1-2 months and should not be discontinued until the pet cultures negative. Stopping when the pet simply looks well visually frequently leads to recurrence of the disease.
This medication must be given with a fatty meal in order for an effective dose to be absorbed by the pet. Persian cats and young kittens are felt to be sensitive to its side effects which usually are limited to nausea but can include liver disease and serious white blood cell changes. Cats infected with the Feline Immunodeficiency Virus commonly develop life-threatening blood cell changes and should never be exposed to this medication. Despite the side effects, which can be severe for some individuals, Griseofulvin is still the traditional medication for the treatment of ringworm and is usually somewhat less expensive than itraconazole.
For more information on Griseofulvin, click here.
This medication is highly effective in the treatment of ringworm but is available in capsules far too large to be useful to most small animals. This means that a special company called a compounding pharmacy must custom make the medication into a more useful size. Nausea is a potential side effect for this medication but probably the main reason it is passed by in favor of griseofulvin is expense. On the average, cats treated with itraconazole and nothing else were able to achieve cure two weeks sooner than cats treated with Griseofulvin.
For more information on Itraconazole, click here.
TERBINAFINE - Worth Mentioning
This is a newer antifungal on the scene and seems to be effective against ringworm fungi. It is, however, expensive relative to the other medications and likely does not offer an advantage.
For more information about Terbinafine click here.
LUFENURON (Program®) -Worth Mentioning
Lufenuron is a flea control product which is given to the pet orally or by injection. The flea drinks the lufenuron in the pet's blood and then becomes unable to make chitin, the material composing the insect's exoskeleton. This is not a problem for the flea as it already has its exoskeleton but it is a problem for any eggs laid by the flea as the larvae inside will not have the chitin egg-tooth they need to break out of the shell. Further, larvae that consume flea dirt containing lufenuron will not be able to pupate. The flea life cycle becomes highly compromised by introducing lufenuron into the system and since mammals do not make or need chitin, there is no effect on the pet.
It turns out that many fungi, including dermatophytes, have chitin in their cell walls. This led to a great deal of research as to whether lufenuron could prevent ringworm or might facilitate recovery from ringworm. Doses far greater than those used for flea control are needed and some studies have published good efficacy while others have shown no effect. This treatment remains controversial as to whether or not it actually works but it certainly is not harmful.
Lufenuron is the flea-sterilizing ingredient in both Program® and Sentinel®.
For more information about Lufenuron, click here.
TOPICAL TREATMENT FOR INFECTED PETS
Both the above medications work by inhibiting fungal reproduction rather than by directly killing the fungus. This is fine from the pet's perspective as either medication should be able to clear the fungus without further therapy; however, we also would like to reduce contamination of the environment. This means actually killing the fungus on the pet so that the hairs dropped will not be infectious. Killing the fungus on the pet means Topical Therapy. For many years cats with ringworm lesions were shaved to allow for easier topical treatment. We now know that shaving may be spreading the fungus, thus shaving is not always recommended (depending on the number of cats present in the home and the length of the hair).
Miconazole (an antifungal) and chlorhexidine (a disinfectant) synergize each other when combatting ringworm. They are available as a combination rinse as well as shampoo. The rinse, which is allowed to dry on the pet, is effective in killing ringworm spores though in the field lime sulfur seemed associated with faster cure.
The problem with decontaminating the environment is that very few products are effective. Bleach diluted 1:10 will kill 80% of fungal spores with one application and any surface that can be bleached, should be bleached. Vigorous vacuuming and steam cleaning of carpets will help remove spores and, of course, vacuum bags should be discarded. To reduce environmental contamination, infected cats should be confined to one room until they have cultured negative. The rest of the house can be disinfected during this confinement period. Cultures of the pet are done monthly during the course of treatment.
Once a cat cultures negative and is removed from the contaminated room, decontamination should be achieved in 1 to 3 cleanings.
The ringworm fungus can remain infective in the environment up to 18 months, maybe longer.
When there is a pet with ringworm in the home, all other pets should be tested. A carrier of ringworm is one that is infected but not showing lesions (usually this will be the pet that has been on treatment for a while and appears visually to be cured but in fact is still infected) or one that is simply carrying the fungus on its fur in the same way an inanimate object might have fungal spores on its surface. Both types of "carriers" must be identified as they are both capable of spreading the infection.
The MacKenzie Toothbrush Test is the best approach to the pet with no obvious lesions. Here the pet is combed with a clean toothbrush and the hair that comes off is cultured for ringworm. This allows sampling of the whole cat when no lesions are visible either with the naked eye or with the Wood's lamp.
WILL RINGWORM GO AWAY BY ITSELF?
There have been several studies that showed that this fungal infection should eventually resolve on its own. Typically, this takes 4 months, a long time in a home environment for contamination to be occurring continuously. We recommend treatment for this infection rather than waiting for it to go away.
WHAT TO CHANGE IF THE OUTBREAK SEEMS TO GO ON FOREVER (LIKE OVER 100 DAYS)
After a couple of months of medication and dipping, the outbreak is generally over. If the outbreak is still going strong, then it is time to look for corners that may have been cut and holes in the program that need patching:
If you yourself become infected, contact your doctor to receive treatment. Veterinarian are not able to make recommendations for human disease or infection, even if the infection came from a pet.
Page last updated: 2/5/2012