Ringworm In Your Dog, Cat And Other Pets

Ron Hines DVM PhD

You can look over some other causes of hair loss in pets  here
Idexx Lab’s PCR Test #3565 will verify ringworm. Results are returned to your vet in 1-3 days vs 21-28 days for the older less accurate test that grew the fungus. (ref)

What Actually Is Ringworm?

Ringworm is not a worm – it is a fungus. The medical term for these fungi are dermatophytes (the infection = a dermatophytosis). When your dog or cat has caught this infection, it often assumes a ring-shaped, scaly, reddened area(s) on your pet’s skin. There are three major fungal organisms that can cause it, Microsporum   canis, Microsporum gypseum, and Trichophyton. In dogs and cats microsporum are the most common forms.

What Animals Can Catch Ringworm?

All mammals can contract ringworm – including you and I ! Veterinarians see it most frequently in cats, but it is also commonly seen in rabbits, dogs, chinchillas and hedgehogs. You can read about the many kinds of animals ringworm affects here. All animals, unless they are immunosuppressed, eventually become immune to ringworm and do not show further signs of the disease. This recovery often takes several months. Unfortunately, some of those pets remain silent carriers of the fungus with the ability to pass it on to other pets – or their owners.

Ringworm In General

Cats – especially long haired cats – often have multiple ringworm sites on their bodies. I see it most often in their kittens – particularly those that have been stressed or housed in large colonies. It is also common in shelter kittens. Many dogs only have a single lesion. Again, it is most common in puppies and immature dogs. Cats that recover from ringworm can remain carriers of the fungus with no external signs. Because the fungus can transfer to humans, it is best to wear gloves when treating ringworm or playing with infected pets. I turn off the exam room lights and scan all new puppies and kittens for ringworm with an ultraviolet lamp on their first visit to my hospital.

What Are The Common Symptoms Of Ringworm?

The Common signs of ringworm are typically circular patches of broken hair in ring-like whorls. These areas usually heal at their centers, growing new hairs a bit darker than the rest of the pet’s normal hair. Surrounding this darkened area is a band of inflamed, reddened skin within which the hair shafts are broken off short. The most common areas for ringworm to occur are the face, ear tips, tail and paws. When these areas are examined with an ultraviolet light source the broken hair shafts often fluoresce. In the very few cases where the lesions are itchy, the skin is crusty and bumpy and infected with bacteria.

How Would My Pet Catch The  Ringworm Fungus?

Ringworm fungus does not penetrate normal skin. The fungus spores passed into a fresh scratch or scrape on the same or a different animal. That can be a scratch from another pet, from a sharp object contaminated with fungus spores or a pet scratching itself due to fleas. The usual source of the spores is a carrier pet that showed no signs of the disease. Not all pets in a household that are exposed to ringworm fungus will develop the disease. Some pets probably never become infected while others do become infected but develop no overt signs of the disease. But some of those animals go on to become silent carriers that spread the disease to others. Another common method of transmission is contaminated grooming supplies and electric hair clippers. The vast majority of dogs and cats that become infected with ringworm eventually cure themselves or become lesion-free even if left untreated. Some cases, however, are persistent and do need medical treatment. Vets treat all cases because they are a public health concern, a threat to other pets, unsightly and can take months to heal on their own. They can also occur on sensitive areas like the eyelids. Although unconfirmed, many veterinarians and public health officials also believe that treated pets are less likely to laps into silent, long-term carriers of the fungus.

How Will My Veterinarian Diagnose Ringworm In My Pet?

Some cases of ringworm are so classical that diagnosis is quite easy and does not require growing the fungus in the laboratory. Veterinarians keep a small portable ultraviolet light called a Wood’s Lamp in their offices. It is similar to the black lights you see in disco clubs and bug zappers. In a darkened room, about 70% of ringworm infections will glow under these lamps. The test is not infallible, dried skin crusts, weepy wounds and lesions caused by mange mites can also glow. But when the typical fluorescent stippling is confined to the hair shafts themselves, the problem is almost certainly ringworm. Veterinarians learn to recognize the subtle differences through experience. In cases where the hair shafts do not glow, one can sometimes see the fungal filaments when cleared individual hairs are examined under a microscope. You vet may pluck a few suspicious hairs from the area and send them off to a lab. There, those hairs are placed on a special growing material (sabouraud’s agar). On that Jello-like material, the fungus will slowly grow. These fungi grow very slowly – so it can take three to four weeks before the results are returned. More recently, laboratories have begun offering a PCR test that is much quicker. There is a link to the Idexx lab test at the top of this page.

How Can Ringworm Be Successfully Treated?

Topical Creams And Ointments

First, infected pets should be separated from those that show no evidence of the disease. I like to clip the area of the infection and then vigorously scrub it frequently with “tame” iodine (povone iodine, Povidine®, Betadine®) scrub (do not use tincture of iodine). Iodine scrub kills fungus (fungicidal) and also removes much of the infected skin flakes that spread the disease. The most common topical treatments to cure ringworm are lime sulfur, enilconazole or miconazole/chlorhexidine shampoos. They work equally well on dogs and cats. Do not apply them near your pet’s eyes. For isolated small spot, three medications, over-the-counter terbinafine (Lamisil® cream), clotrimazole (Lotrimin®) and miconazole ointments are sometimes effective. When the areas are not being pre-cleaned sufficiently with a medicinal scrub, these medications are unlikely to work as well.

Vacuum your house and scrub down kennels to remove fungal spores. Throw away the vacuum cleaner bag once you are done. Be sure to wear gloves when you treat or handle infected pets so you don’t become infected yourself or spread it to other pets. Disinfect grooming aids and pet bedding between use.

Oral Medications

Itraconazole (Sporanox®) and oral terbinafine are the most common oral medications given to pets to eliminate ringworm. An older medication. griseofulvin (Fulvicin®) tablets, will also kill ringworm. But it must be given for extended periods of time (4-8 weeks) and side effects sometimes occur. Griseofulvin must never be given to pregnant animals or people. Cats with concurrent immunodeficiency disease or feline leukemia may not tolerate it and, due to their weakened immune systems, may relapse with the fungus later. I would avoid the drug entirely since itraconazole and terbinafine are considerably more pet and household friendly. There are also an unacceptable number of treatment failures with griseofulvin. (ref) You can read the most current guideline on ringworm treatment and ringworm in general here.


A vaccine claimed to prevent or lessen the severity of ringworm is marketed by Wyeth’s Fort Dodge division. (ref) I do not believe that the vaccine is effective. But in their desperation to rid their catteries of the problem, some catteries and cattery vets administer the vaccine. Kittens least likely to have this disease are from individual litters born in a residential setting. That is, the more cats at an institutional home or facility, the more likely ringworm is to be present. The same advice goes for puppies. Do not share grooming aids, clippers, bedding, cages, etc. between pets. Catteries can cleanse themselves of this problem by doing fungal cultures or PCR tests on each cat in the cattery. This includes those cats that show no symptoms whatsoever. All positive cats should be treated with itraconazole. Long-haired cat catteries seem to me to suffer more from this disease. I do not know if that is due to their excessive hair or if purebred, long haired cats are frailer in their immune defenses than domestic short hair cat breeds. A good household anti-fungal disinfecting solution is a one in twenty solution of household bleach and water. You must not use this on your pets or introduce the animals back into the area until the smell of bleach has completely dissipated.

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