Ringworm is not a worm, but a fungus. It tends to be more of a problem in catteries where there are large numbers of cats. In cats, ringworm usually appears as a dry, gray scaly patch on the skin. In people, ringworm appears as a round, red, raised itchy lesion with a ring of scale around the edge.
Cats may come in contact with infectious fungal spores in the indoor or outdoor environment. Contaminated soil is a common source of infection, as are other cats infected with ringworm. Not all cats that are exposed to fungal spores develop a fungal infection, however, a cat may not show clinical signs of the disease but can serve as carrier.
Infected cats continually drop fungal spores from their skin and fur. These spores can remain capable of causing infection for many months, and are difficult to eradicate from your household. Children and the elderly, as well as those with suppressed immune systems, are particularly at risk of infection.
Because ringworm is infectious, cats with the disease should be quarantined within your home until it is cured. All cats within the household should receive topical therapy, which may include clipping down the hair and applying an antifungal ointment to the skin or shampooing and dipping the entire cat in medicated products. The examining veterinarian will recommend the best approach depending on the location of the lesions. Topical treatment should be continued until a negative fungal culture is obtained.
Cats that do not appear to respond to topical treatment within two to four weeks may be given supplemental oral drug treatment in order to eradicate the infection more quickly. The most commonly used oral antifungal medication is griseofulvin, which is used to treat cats that do not respond to topical treatment. However, some cats cannot tolerate griseofulvin and may develop a serious side effect of fatal bone marrow suppression. Therefore, complete blood count tests are performed on cats taking this drug to watch out for evidence of bone marrow problems. Ketoconazole and itraconazole, two drugs that are not currently licensed for the treatment of ringworm in the United States, are used effectively as an alternative to griseofulvin for cats that cannot tolerate this medication.
A vaccination against Microsporum canis has been developed for cats, but the safety and efficacy of this vaccination still needs to be researched. The use of the vaccine may be recommended in frustrating cases of ringworm infection.
Infections can be very difficult to eradicate in multiple cat households or breeding facilities and often require consultation of a veterinary dermatologist. Humans should wear gloves while treating the infected cat and follow the recommended protocol for avoiding infection, including a thorough disinfection of the indoor environment. If human infection does occur, prompt medical attention is advised.
We recently saw a very persistent case of ringworm in a multiple cat household. The elderly owner purchased a new Persian kitten from a reputable cattery and added it to her other four Persians. Within a few weeks, the other cats were exhibiting symptoms, as was the owner. After a very frustrating eight months of consultations with veterinary dermatologists and the re-infection of the cats and owner, the problem was finally eradicated. It is always a good idea to isolate new arrivals in your home for a few weeks and have them examined before adding to the rest of your cat population.
Sharon E. Anderson, DVM
