Ringworm
by Melissa Rotella, DVM

Alden is a one year old male cat from a local animal shelter that presented to Route 516 Animal Hospital for an upper respiratory infection. While treating the infection, the staff noticed an area of hair loss on his left front foot. The lesion was grey with some scaling and crusting where the hair was missing. Based on the appearance and fungal culture results, Alden was diagnosed with ringworm and treatment started immediately.

Despite the name, ringworm is not an actual worm or parasite. In fact, ringworm is a fungal disease known as dermatophytosis. There are several species of dermatophyte fungi. Microsporum canis is the most common species of ringworm and dogs and cats are the normal host. Microsporum gypseum, which is found in the soil and trichophyton mentagrophytes which has a rodent host are the two other species of ringworm. The fungus lives on skin and feeds on dead cells in the skin, nails, and hair leading to skin infections in mammals, including humans. The term “ringworm” is derived from the way the lesion appears on the skin of humans. The classic appearance in people is a red, irritated area of skin with a ring of scaling around the edge of the lesion.

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Ringworm can be seen in all our household pets, but tends to be more common in young cats and kittens. There are even some pets that can be a carrier of ringworm. A carrier animal does not show lesions but is still infected and able to pass the disease to other animals and people. Carrier animals, along with the fact that ringworm can survive in the environment (soil) for up to 18 months, make treatment and resolution difficult at times.

A diagnosis of ringworm starts with a physical exam and a suspicion by the doctor. The appearance of lesions can vary between animals but a typical lesion is a circular path of hair loss with inflammation, scaling, and crusting. Some owners will notice their pets scratching or chewing at the lesions, but the pet may not always be itchy. One species of the fungus will fluoresce an apple green color when the lesion is placed under a black light in approximately 50% of cases. A fungal culture is usually needed to confirm a diagnosis of ringworm. It takes at least 10 days for the fungus to grow and therefore many times topical treatment will be initiated prior to confirmation to prevent further spread of the fungus.

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Medial management and disinfection of the home environment are the two main approaches of treatment. The affected hair should be clipped and topical anti fungal creams applied daily. In addition, oral antifungal medications and antibiotics (to treat secondary infections) are added to the treatment plan. Oral antifungal medications can be relatively expensive and have the potential for side effects. It is important that any pet started on oral antifungal be closely monitored for side effects. In the home, affected animals should be confined to one room, away from other pets. Prognosis for most animals is good; however treatment may need to be continued for several weeks to months.

Alden was started on clavamox (an antibiotic) and itraconozle (an antifungal) along with topical medication and weekly bathing. After a month of treatment, Alden was found to be free of ringworm and adopted to a new loving home. His new owners report that he is doing wonderful!