Ringworm (Dermatophytosis)

Microsporum canis - Colony on SGA 3 weeks old

Ringworm in a lab culture (not a diagnostic specimen, provided here for reference).

Colonies (SGA) spreading thin, woolly, strongly radiating, greyish- to tannish-white; reverse deep ochraceous-yellow.

Tinea capitis caused by Microsporum canis

Ringworm on a 7 year old person

A 7 year old male developed a crusted area on the left temporal scalp with associated hair loss. He had recently visited his Grandparents' farm and was in contact with several of the barnyard cats.
Culture grew Microsporum canis.
The patient responded to a 8 week course of oral griseofulvin.

A Fungus Among Us

It seems that a few dogs are showing up with "Ringworm." To set the record straight, please know that the name ring worm is an old fashioned misnomer based on the appearance of the ring like skin lesions. Ring worm is actually "a fungus among us."

This fungus is everywhere. Microsporum canis is in the ground and in the air. Little spores will land on susceptible skin and grow in a red circle ring like rash.

Cats can get dog ringworm and they get scaling of the skin and show local lesions that look like "cigarette ash" deposits. Infection in cats is often not noticed.

Kittens and puppies are most often affected as their immune system is not yet developed enough to resist the fungus.

Young dogs will show a few to many patches of hair loss and scaliness and redness at the out side edge (the ring). Some cats and dogs will develop infection of the nail beds. Often a thick crust will cover the lesion.

Dermazol or Selsan Blue Shampoo and itraconizole will reduce the lesions and may cure the disease. Serious cases require itraconizole therapy or diflucan therapy.

Some feel that the new ringworm vaccine may help: however, it is not widely used by the profession. The best thing to do if you suspect you or your pet has a skin disease is to see your veterinarian for some tests. A skin culture and a skin scraping generally tell the story.

Most pets and people develop an immunity to fungal diseases and don't have to worry. Have fun at the dog park and go on!

Lab Animal Diagnosis

Ringworm (Tinea corporis)

The doctor correctly diagnosed the lesion as ringworm, or dermatomycosis. It is caused by the growth of fungi known as dermatophytes, which parasitize the surface of the skin or hairs because of their ability to use keratin. In humans, ringworm is typically manifest as a small, red macule with a scaly center that spreads to an inflammatory border. There is considerable variation in the clinical appearance, ranging from single or multiple rings, and from slight inflammatory reaction to marked vesiculation, exudation, pustulation, and crusted patches 1. The lesions of zoophilic or animal-transmitted fungal infections are more inflammatory in people than those caused by fungi transmitted person-to-person 2.

The term "ringworm" comes from the erroneous belief that the lesions are caused by a worm that burrowed under the skin. Although dermatomycosis may occur anywhere on the body, in human medicine it is traditionally divided into five categories, based on the anatomical location of the infection1: tinea capitis (ringworm of the head, beard, and scalp); tinea corporis (ringworm of the body) or "jock-itch"; tinea cruris (ringworm of the groin); tinea pedis (ringworm of the foot) or "athlete’s foot"; and tinea unguium (ringworm of the nails). In veterinary medicine, the terms ringworm or dermatomycosis are used to describe the infection anywhere on the animal’s body.

Dermatomycosis can be associated with either human, animal, or soil contact 3. Some species of dermatophytes such as Trichophyton tonsurans or T. rubrum are anthrophilic or host-specific for humans and transmitted only by person-to-person contact. The most common etiological agents of ringworm are zoophilic or animal-to-human transmitted fungi and are Microsporum canis from cats and dogs 2-4, and T. mentagrophytes from various animals including rodents 2,5. Another species of dermatophyte, T. verrucosum, is also zoophilic and is associated with infection from cattle6. One species of fungus, M. gypseum is geophilic and acquired from contaminated soil 3.

To diagnose dermatomycosis in either animals or humans, one should examine a potassium hydroxide preparation of skin scrapings microscopically for the presence of fungal spore clusters. It is also necessary to perform fungal cultures of the skin and hair. Fungal growth may be slow, and a positive result cannot be ruled out until the culture is negative for at least three weeks. Consequently, diagnosis is made most commonly by clinical appearance and microscopic examination of skin scrapings. Dermatophytes such as Microsporum spp. will fluoresce under an ultra-violet or Wood’s Lamp, and this method is commonly used to diagnose ringworm in animals 1. However, Trichophyton spp. infections will not fluoresce, and scrapings of skin lesions and hair for microscopy and culture should be taken if dermatomycosis is suspected and the animal is Wood’s Lamp-negative 1,4. Irrespective of the etiological agent of ringworm, treatment consists of the application of a topical fungicide such as miconazole, clotrimazole, econazole or tolnaftate for 4-6 weeks. If the response to treatment is unsatisfactory, or in severe cases of dermatomycosis, systemic treatment with fungicides such as griseofulvin or ketaconazole is recommended as an adjunct therapy 2.

The result of the culture came back, and the cause of the ringworm in the animal technician was identified as M. canis. Based on this, it is unlikely that the infection resulted from the rodents, since T. mentagrophytes is the dermatophyte associated with rodents. M. canis infection is more commonly associated with companion animals.

We carefully examined all cats in our facility, and, using a grooming-brush, collected hairs from all animals and performed cultures by combining hairs from three animals per plate. One culture came back positive for M. canis, and we then individually cultured these three animals. During this period, one of the suspect cats developed lesions on the head and muzzle typical of ringworm , and its culture was positive for M. canis. Until lesions became apparent, this cat did not fluoresce under ultra-violet light. We do not have an explanation as to why this cat was asymptomatic for approximately six weeks.

The cause of infection in the animal technician may have been associated with another cat from the vendor, which had been used in an experiment before we had an opportunity to culture it. The positive cat was euthanized, and we contacted the supplier to alert them to our findings. Symptomatic and inapparent forms of dermatomycosis have been reported in a focus of homeless cats, which led to a chainlike transmission from these cats to pet cats, pet dogs, and eventually family members of the animals’ owners7.

     1. Stevenson, W.J. and Hughes, K.L. Synopsis of Zoonoses (2nd edition). Ringworm. Australian
Government Publishing Services, Canberra, pp. 99-106, 1988.
     2. Radentz, W.H: Fungal skin infections associated with animal contact. American Family Physician; 43: 1253-1256, 1991.
     3. Rippon, J.W: The changing epidemiology and emerging patterns of dermatophyte species. Current Topics in Medical Mycology; 1:208-234, 1985.
     4. Katoh, T., Maruyama, R., and Nishioka, K. et al. Tinea corporis due to Microsporum canis from an asymptomatic dog. Journal of Dermatology; 18: 356-359, 1991.
     5. Vendrig, A.A. and Hendrikse, J.C. Fungus infection in a guinea-pig as a cause of human infection. Tijdschrift voor Diergeneeskunde; 103:548-541, 1978.
     6. Kielstein, P. Systematic control of dermatophtosis profunda of cattle in the former GDR. Mycoses; 33:575-579, 1990.
     7. Otcenasek, M. and Zampachova, I. Natural focus of microsporosis caused by Microsporum canis bodin. Folia Parasitologia; 27:173-182, 1980.


By Kimberly Meenen
Information Specialist
University of Illinois
College of Veterinary Medicine

Ringworm or dermatophytosis is an infection of the hair and hair follicles caused by certain types of fungi. These fungi can affect many species of animals and also humans.

"Ringworm is commonly seen in many animals including dogs, cats, and farm animals," says Dr. Kevin Byrne, a veterinarian and resident training in dermatology at the University of Illinois College of Veterinary Medicine in Urbana.

Animals can spread most types of ringworm to humans. Ringworm is the most common zoonotic disease
transferred from animals to humans. Studies show that the rate of infection is increasing.

If your pet develops a suspicious skin lesion, consult your veterinarian. Minimize your contact with the animal until the problem can be diagnosed. Good hygiene is extremely important. Wash thoroughly after handling your pet. If you develop a lesion, consult a physician immediately.

Cats and dogs infected with ringworm often experience hair loss on their heads or faces. Hair loss can also occur on other areas of their bodies. Hair that remains is usually short and coarse. Redness and itchiness may develop. Some animals with ringworm will show no apparent lesions but can transmit the infection to others.

Dr. Byrne explains that three types of ringworm are most commonly seen in dogs and cats. Microsporum canis (M. canis) is the usual cause of ringworm in cats. A few cats can be symptomatic carriers of M. canis. These carrier cats can transmit the spores to other cats or to other animals and humans. Microsporum gypseum (M. gypseum) can exist in the soil. Dogs and cats can become infected with M. gypseum by digging in the soil. Trichophyton mentagrophytes (T. mentagrophytes) typically comes from rodents and often affects dogs and farm animals. Often, it is very difficult to identify the source of infection.

Veterinarians can use a number of methods to diagnose ringworm. The most reliable test is a fungal culture. This involves culturing hairs or scales from the infected animal and observing the culture for a color change. Other means may include using a fluorescent light (Wood's Lamp) to detect certain strains of M. canis or examining hair specimens under a microscope.

If your pet has ringworm, your veterinarian will develop a treatment program depending on the extent of the infection and number of animals involved. Recommended treatment may include oral and/or topical antifungal medications. Trimming around the lesions may also be helpful. Scratching can cause further trauma to the lesion and spread spores. Isolate an infected cat from other cats as grooming may also spread fungal spores.

Dr. Byrne notes that for years ringworm treatment for cats included clipping the entire hair coat. Current findings from the University of Wisconsin show that in some cases clipping the entire cat actually helps spread ringworm across the body. However, clipping the entire coat may be needed for severe generalized infections and may help limit the spread to other animals or people.

It's also important to clean up the contaminated environment (i.e., floors, walls, behind the refrigerator). Use a disinfectant solution made of bleach. If possible, dispose of all pet bedding. If this is not possible, wash with a recommended disinfectant detergent.

When purchasing a new cat or dog, Dr. Byrne advises to check the animal's hair carefully. If hair is missing or short, these are clues that ringworm could be present. The patches should be cultured for ringworm before bringing the cat home.

Successful treatment can take several months. If the environment is contaminated it can be a long-term problem. Although a normal healthy cat can clear up an infection on its own in 3 to 4 months, the threat of reinfection will always exist, says Dr. Byrne. "It's better to initiate an aggressive treatment plan to rid a cat or dog of ringworm. Owners can stop treating for ringworm when fungal cultures generate negative results," he concludes.

A vaccine for ringworm is now being marketed. However, tests at the University of Wisconsin show that the vaccine does not offer full protection against infection. Although the vaccine may decrease redness or other symptoms of ringworm, other therapy would probably be needed to clear the infection.


An occasional cause of skin conditions in pets is caused by Ringworm. The scientific name for this disease is Dermatophytosis. It is caused by a fungus not a worm, and the lesion is not always in the shape of a ring. Since fungi are everywhere in our environment, it is difficult to determine which pets will develop the problem. The fungus that causes Ringworm can be cultured from the hair coats of normal dogs and cats. These pets might be carriers of the disease to other pets along with people. We tend to see the problem more in young animals.

People will sometimes pick up a case of Ringworm from their pet, but just because a pet has Ringworm does not necessarily mean that the people that interact with that pet will develop the problem. A dog or cat can transmit Ringworm to a person without showing any symptoms at all.


There are 3 specific fungi of significance in this disease.

Microsporum canis
The source of this species of Ringworm is almost always a cat.

Microsporum gypseum
This species of Ringworm is usually from dogs and cats that dig into contaminated soil.

Trichophyton mentagrophytes
This species infects dogs and cats when they are exposed to rodents or the burrows they live in.

In cats, almost all cases of Ringworm are caused by Microsporum canis. In dogs the majority of cases are caused by Microsporum canis. Which of these 3 main dermatophytes causes the Ringworm in dogs depends on geographic location.


The skin lesions that appear with Ringworm are variable, and do not necessarily form a ring. There will be hair loss, usually in small patches at first. As time goes on the patches may disappear or appear at other locations on the skin. There might be scratching due to itchiness. If the hair loss occurs on the face or feet there is a chance it is due to digging habits or exposure to rodents.

Ringworm on a Dog     Ringworm on a person
This patch is typical of the lesion seen in Ringworm. (dog - left; person - right) A diagnosis of this disease can not be made based just on the appearance of this lesion because other skin conditions (Demodex for example) can show similar lesions.


There are several different ways to diagnose Ringworm. All require some type of test because it is impossible to make the diagnosis just by looking at the skin. This concept holds true for all skin conditions; making a diagnosis of a skin disease requires all of the aspects of the diagnostic process.

If a person in a household has been positively identified with Ringworm by their physician it is possible they obtained it from their pet, even if their pet has no symptoms of the disease. This is especially important in multiple cat households. We will culture these pets using the culture technique we describe below, but in this case, we might run a new toothbrush over the hair coat to obtain a sample for culture.

One of the simplest ways to diagnose Ringworm is with the Woods lamp, which is an ultraviolet lamp, also know as a black light. 50% of the Microsporum canis species will fluoresce when the Woods lamp is placed near the area of hair loss.

The blacklight, er, Wood's Lamp
The lamp emits a purple/blue glow from the tube, and when there is fluorescence on the skin, it has a greenish appearance. Other material on the skin (dander, medication, etc.) can also fluoresce, so interpretation is important.

Since only 50% of a certain species of Ringworm fluoresces under the glow of the Woods lamp, a culture is used to verify the diagnosis:

Ringworm on a dog - Diagnosis by Hair Plucking for Culture
The first step in the culture process is to gently remove hair follicles in the area of the lesion

These hairs are cultured in a special media that inhibits bacterial growth and enhances fungal growth. This culture can be done in house. Since a fungus is a slow growing organism it can take up to several weeks to determine if there is growth or not.

This positive culture demonstrates two findings that are needed for a positive diagnosis. The first is the cottonish fungal growth, and the second is the reddish color of the culture media. This color change must occur at the same time the fungal growth appears.

 Ringworm Positive Culture at 10 days
Positive fungal growth after 10 days of incubation at room temperature.

Topical shampoo therapy is used in almost every case, especially in longer haired pets. It is common to clip some or all of the hair in some pets to make it more effective. These baths will also remove infected hairs that can be the source of an infection to people or other animals.

Specific anti fungal cremes are also used when a pet is infected in an area that already has sparse hair growth, or there are small, discrete lesions.

Oral anti fungal medications are also used in select cases. They have the potential to cause side effects, so their use is confined to specific situations.

In some pets the disease may resolve by itself.


Since fungi are everywhere it is almost impossible to prevent exposure. Pets that chase rodents, especially into burrows, might be at an increased risk.

Dermatophytosis aka "Ringworm"

Ringworm is a common kitten problem.

First of all, ringworm has nothing to do with worms! It is a fungal infection of hair follicles leading to loss of hair in the affected areas. It may or may notform a scaly or crusty ring. I see it most often on the face or ears of kittens or cats, but it can infect any part of the body that is furred.

Ringworm is normally a self-limiting infection which means that a cat will eventually get rid of the infection even without treatment, if the cat has a normal immune system.

So why treat the infection? We generally treat ringworm to limit the spread of of infection to other fur bearing animals and people. Children are especially vulnerable. The infection is spread by infected hairs or spores in soil.

Your veterinarian will usually do an initial screening for ringworm with a Wood's lamp (a "black" UV light). Hairs infected with one type of ringworm fungus, microsporum canis, will often fluoresce bright green under ultraviolet light. Other strains will not fluoresce so the Woods lamp test is only positive about 50% of the time.

There are other more accurate tests your veterinarian may use. I do a fungal culture by plucking a few hairs from a suspicious looking area and placing it in a special medium that will change color within 14 days if the fungus that causes ringworm is present and starts to grow.

Treatment consists of:

If you suspect you or a family member might have ringworm, please check with your family physician. If your cat has any areas of hair loss or crusting, please take him to your veterinarian for a checkup. Ringworm is just one possibility.

Feline Ringworm (Dermatophytosis)

Feline Dermatophytosis (FD) is a common infection of the superficial layers of cat skin by a fungus. The incidence is extremely variable depending on geography and individual environment and may approach 20-30 % of all cats in some areas. Most FD is caused by Microsporum canis. Microsporum gypsum and Trichophyton mentagrophytes are uncommon causes of FD. M. canis also caries the potential to infect humans. The incidence of FD is probably increasing as the popularity of cats increases in our fast paced society.

The disease represents an infection of the top layer of dead skin including hair shafts and nails. The organism multiplies in the dead tissue producing numerous spores that shed into the environment for future infection. Spores are extremely resistant. M. canis is probably an opportunist with specific requirements for infection. Infection is dependent on the health of the animal, stress factors, numbers of spores available to infect, and possibly genetic predisposition. Specifically, harboring the organism in the skin of a cat does not always produce disease. Unapparent carriers occur with frequency and therefore the potential for human exposure is exists. Cats showing obvious signs of FD are shedding the organism and present the greatest threat of infection to other cats and people. cats that are asymptomatic are probably just moving the organism around as a carrier and pose only a small risk that could be managed with good hygiene.

FD is often confused with many other causes of dermatitis. Signs of the disease vary and FD is always a consideration in any feline skin problem. Common leisons affect the head and extremities most often. Signs include hair loss with redness and scaling skin. FD can be associated with an itch but many cases are with out irritation. Some cats will only show an area where hair shafts are broken and no other signs. About half of FD that is caused by M. canis will fluoresce. The diagnosis is made by clinical signs(which may include fluorescence) and a positive fungal culture. Occasionally, the veterinarian using microscopic examination will confirm spores of FD along the hair shafts. A fungal culture is the gold standard for a diagnosis.

Treatment for FD consists of topical, systemic and environmental control. FD is often self limiting by the cat¹s immune system. However, shortening the duration diminishes the spread of the disease to other individuals. Probably all modes of therapy should be used together to shorten the course of the disease. Although environmental control is an important part of treating FD outbreaks it remains the most frustrating because of a lack of good products. There are very few products that will actually kill M. canis. They include bleach and formaldehyde. Both are impractical for most households but may have a role in some catteries. Currently, the best environmental control is by good cleaning to pick up the spores and dispose of them carefully. These are old methods of steam cleaning, vacuuming, washing clothes and bedding in bleach and mopping floors.

Topical therapy serves more to limit environmental contamination than effecting a cure. It is an important aspect of decreasing contamination in the environment and infecting other individuals. Clipping cats prior to topical treatments has been suggested but is controversial. Great care is required not to contaminate the environment with the spores shed from the clipping and therefore, any grooming should be done in an isolated area. Also, clipping should be coarse to minimize the spread of the spores over the patient. Topical treatment consists of  either shampoos or creams. These products contain disinfectants such as lime sulfur, povidone iodine, chlorhexidine or imidazole agents that are specifically antifungal.

Systemic therapy is very effective. Two groups of drugs exist. In addition, a vaccine has been released for treating FD due to M. canis infection. The first drug used, Griseofulvin has been used for 50 years with good success. The oral imidazoles are newer, more expensive and, have more short term side effects such gastrointestinal upset. The drugs are administered orally with a fatty meal to reduce the GI side effects. Use of griseofulvin in pregnant cats, immunsuppressed animals, or current breeding cats, male or female, is contraindicated. The imidazoles have also been shown to cause birth defects in pregnant queens. Currently Griseofulvin appears to be the most effective drug available however, with newer experimental imidazoles this may change. Generally, treatment lasts approximately 8-10 weeks or specifically 2 weeks beyond the resolution of signs. It may be best to treat far beyond signs, such as 4-6 weeks. Other protocols suggests 2 weeks beyond 2 negative cultures.

Most recently, a killed vaccine is being used to treat difficult cases of FD in addition to current drugs. Results have been good and, the vaccine may have some prophylaxis potential. The vaccine is currently being marketed and is available through veterinarians.

It is important to recognize that although FD is relatively easy to treat it presents a significant challenge to remove from the environment. Therefore, it is advisable for multiple cat households or catteries to consider testing all new cats prior to their admission to the group. Multiple samples should be collected from the individual for culture. Many veterinarians will use a new (packaged) toothbrush to brush over the cat and obtain many samples to embed into the culture media.