The fungal infection known as ringworm can be extremely difficult to eradicate. This is because it spreads readily by means of spores that can remain viable in the environment for up to 2 years, it's highly contagious to other cats (as well as to other animals and humans) and it has a long incubation. The topical antifungal tolnaftate, developed to treat ringworm and other fungal infections in humans, may work as a feline ringworm cure, but only in cases of limited infection.
Microsporum canis is the fungus species that causes 90 percent of feline ringworm cases. Fungal organisms called dermatophytes, attached to a cat's haircoat, shed spores through the air on hairs and dust. Infectious spores in the environment--on rugs, bedding, brushes, furniture and clothes--remain viable for 15 to 24 months, according to the Feline Advisory Board.
Once attached to a cat's haircoat, spores surround hair shafts and germinate at the follicle, invading the upper layer of the cats' skin and forming colonies of dermatophytes that feed on keratin from dead skin tissue and hair. The metabolic activity of the dermatophytes causes skin irritation and hair loss that manifests as ring-shaped lesions on the cat's ears, head or tail. Lesions are often scaly and irritated and may be itchy. They may also be irregular in shape and found elsewhere on the body. Generally, lesions appear within about 10 to 14 days of a cat’s contamination by spores--but incubation can last for 3 weeks, making isolation of infected cats difficult in a multicat household.
Topical Spot Treatment
According to the Feline Advisory Board, a topical cream or ointment applied to a cat's lesion is unlikely to kill the fungus entirely. The infection will likely extend beyond the boundaries of the lesion, making complete coverage difficult. This would be true of the veterinary products miconazole (prescription required) and clotrimazole (available over the counter) as well as the human ringworm topical tolnaftate (OTC). Another drawback is that spot application will not get rid of spores that may be present elsewhere on the cat's coat.
Tolnaftate as Antifungal for Skin
Tolnaftate was developed to treat human cases of ringworm on the skin (tinia corporis) as well as athlete's foot (tinea pedis) and jock itch (tinia cruris). It's not even meant for the scalp or nails. The website of one tolnaftate product, Tinactin, clearly states that this topical "cannot penetrate through the thickness of your nail or all the way down to the roots of your hair." In her pet health care column, veterinarian Dr. Deborah Lee Pickett advises that tolnaftate is ineffective for cat ringworm cases, as it does not penetrate hair follicles where dermatophytes dwell. To kill the fungus topically, she recommends using a veterinary antifungal product instead.
Many cases of ringworm call for systemic oral medications, which penetrate hair follicles and prevent replication of fungal cells. A veterinarian will likely treat with oral meds when: a cat's infection has not resolved within 4 weeks of topical treatment, lesions are widespread, the nails are infected, cats are long-haired, or many cats in a household, shelter or cattery are involved. One highly effective oral drug is griseofulvin; however, it produces adverse gastrointestinal reactions in many cats. It can also cause birth defects if used to treat pregnant cats and, rarely, bone marrow suppression. Itraconazole is considered effective and is better tolerated. Terbinafine is another good oral treatment option.
Topical Spore Eradication
To more effectively prevent the spread of ringworm, though, you should eliminate spores from a cat's entire coat, so it does not become reinfected or spread spores to other cats (or you). An antifungal miconazole shampoo is a good option, but lime-sulphur dips, though messy and foul-smelling (like rotten eggs), are even more effective. Both are provided by veterinarians. Use such preventive measures if you're dealing with ringworm in a multicat household, a shelter or a cattery for a period of about 6 weeks. You should also thoroughly cleanse the environment by scrubbing with a 10:1 bleach solution and vacuuming every day. Eradication of all spores is key to stopping the spread of ringworm.
If you catch ringworm in your cat early, tolnaftate may help to cure it in limited cases--for example, If it has only one or two very small lesions and is healthy. After all, tolnaftate is an inexpensive, over-the-counter medication, and you might happen to have some at home, (although the veterinary antifungal, clotrimazole, is also a relatively inexpensive over-the-counter product). Beside Tinactin, brands include Absorbine Jr, Blis-To-Sol, Aftate and Ting. Be sure to rub it in about an inch beyond the margins of the visible lesion. But if the lesion persists unchanged for 2 weeks or gets larger or more inflamed, take your cat to the vet. First of all, if it has ringworm, you don't want to lose time trying an ineffective product while its infection grows and it sheds infective spores. If your vet feels reasonably sure that it is ringworm, she may prescribe a more effective antifungal to check the infection even before diagnostic test results are in. A second concern is that other skin infections can look like ringworm, so get a veterinary diagnosis to ensure effective treatment.