What is ringworm?
Ringworm is a common yet serious disease in cats. Because the lesions are often circular ringworm was once thought to be caused by a worm curling up in the tissue. However that is not the case. In fact ringworm is caused by a fungus. The fungus causes an infection in the dead layer of the skin hair and nails. The fungus is able to feed off of the dead tissue as a source of nutrition.

Ringworm is also known as dermatophytosis. There are four types of fungi that can cause this condition; it is most commonly caused by the organism called microsporum canis. Microsporum canis is so well adapted to cats that up to 20% of all cats are thought to be carriers for the disease.

What cats are most likely to get ringworm?
Genetic and environmental influences play an important role in feline ringworm infection. Although more research remains to be done in this area it appears that Persian cats have a higher chance of infection. In feline containment centers (catteries) ringworm can be difficult to control because of the number of animals in close contact with one another.

What are the signs and symptoms of ringworm?
The fungi (plural for fungus) live in hair follicles. As the organism invades and weakens the hair shafts hairs break off at the skin line. Once the hair follicle is invaded the organism grows downward and eventually destroys the hair follicle. The area may become inflamed with ringworm. Patches of hair loss tend to be circular; as the fungi multiply the lesions may become irregularly shaped and spread over the cats body. These patches may be associated with scaling and crusting of the skin. The lesions are sometimes itchy but that is not always the case. In fact there are times when animals are infected by show no signs at all. It must be remembered that there are no set clinical signs that are used to diagnose ringworm.

The incubation period is anywhere from 10-14 days. This means that after exposure to the fungus and infection 10-14 days will pass before any visible signs occur.

How is ringworm diagnosed?
Feline ringworm can be diagnosed by four different methods. In some cases more than one approach is utilized. Diagnosis is done by one or more of the following:

1. Identifying the typical ringworm lesions on the skin. This is the least accurate method since other skin diseases may have the same appearance and not all infected cats have visible lesions.
2. Examining the scales and hair under a microscope. Some of the fungal elements such as spores can be seen this way. A downfall with this method is that false positives commonly occur.
3. Placing the infected hairs under a fluorescent light. We recommend using a Woods Lamp Blacklight for this approach. The lamp should be warmed up for 5 minutes and the test should be conducted in darkness holding the lamp over the potentially affected area for 3-5 minutes. This screening test is useful because Microsporum canis will sometimes fluoresce as a bright green color under ultraviolet light. Failure to fluoresce however does not eliminate ringworm as a potential diagnosis. The accuracy of this tool is about 50%.
4. Culturing the hair for the fungus. After a few hairs are plucked from a lesion it is placed on a special gel and is then watched for fungal growth. Also the color of the gel will change from yellow to red as the fungus grows. These cultures are checked daily. This method is the most accurate way to diagnose feline ringworm however it can take 7-10 days to get results and in rare cases results may not be visible for 14-21 days.

How is ringworm transmitted?
Transmission occurs by direct contact between infect and non-infected individuals. It can be passed from dogs to cats and vice versa. It may also be transmitted from animals to people well as from people to animals. Adult humans are fairly resistant to infection unless there is a break in the skin or the immune system is suppressed. Children however are highly susceptible.

Transmission may also occur from an infected environment. The fungal spores can live in bedding or carpet for several months. These spores may be killed with a dilution of chlorine bleach and water (1 cup of bleach to 1 gallon water) where it is feasible to use it.

How is ringworm treated?
There are several methods to treating ringworm in cats. The specific method recommended by your veterinarian will depend on the severity of the infection the number of pets involved possible presence of children in the area and how difficult disinfecting the cats environment will be. The most commonly used treatment options include the following:

1. Griseofulvin. This prescription comes in tablet form and works deep in the hair follicles to reach the site of active fungal growth. Administered daily cats with active lesions should receive the tablets for a minimum of 30 days. Griseofulvin is the only drug approved for the oral treatment of feline ringworm. Although effective it does have some potentially significant side effects including gastrointestinal issues possible birth defects in pregnant cats and suppression of bone marrow production.
2. Miconazole Cream or Miconazole Spray are both effective topical treatments. Miconazole products contains the anti-fungal agent Miconazole Nitrate for the treatment of fungal infections such as ringworm and superficial skin infections caused by yeast. Safe for use on dogs cats and horses. Miconazole is only available with a prescription.
3. Malaseb Shampoo is also available only with a prescription. Malasebs unique formulation provides antibacterial and antifungal agents for optimal therapeutic effectiveness.
4. LimePlus Lime Sulfur Dip is another prescription product. Dips should be done twice weekly for the first two weeks and then once weekly for the next 4-6 weeks. Lime Sulfur Dip can also be applied to other pets in the household to prevent spread of infection.
5. Ringworm vaccine. This vaccine helps the cat develop immunity to the fungus. Other products are still combined with it but its use will quicken recovery time. This is especially important if other pets or children are exposed.
6. Shaving of the cats hair. Even though it can be advantageous in some situations some studies have suggested that clipping may cause microscopic nicks in the skin and serve to further inoculate ringworm into the skin. Also clipper blades can spread the fungus between cats. Clipping is most likely to be of help with long-haired cats and in households where more than one cat is infected.

Treatment will not produce immediate results; in fact the areas of hair loss may get larger before they begin to get smaller. Within 1-2 weeks the hair loss should stop and there should be no new areas of infestation. However infected pets may remain contagious for about 3 weeks.