Those darn dermatophytes!

Is this a dermatophyte lesion? Don't judge by sight alone. (Getty Images)

Your clients know dermatophytosis as ringworm and fear that telltale sign on themselves or their pets because of its zoonotic nature. Veterinary dermatologist Dr. Rudayna Ghubash from the Animal Dermatology Clinic in Marina Del Ray, California, has a few pointers for helping your affected veterinary patients and protecting others in the household from a similar irritating fate.

Don't overdiagnose, but don't underdiagnose

If you go by clinical signs alone, Ghubash says you'll likely overdiagnose dermatophytosis. The classic clinical sign is folliculitis-specifically, circular areas of hair loss with scale. But two other dermatologic conditions can cause the same sign-demodicosis and Staphylococcus species infection.

Ghubash says dermatophytosis can also be underdiagnosed because some affected pets don't display the classic sign. If you don't see folliculitis, you probably won't perform fungal testing. Ghubash says dermatophytosis can instead cause signs that might lead you down the wrong diagnostic path-papular eruptions with scale and crusting, miliary dermatitis and varying degrees of pruritus, from the not itchy at all to the intensely itchy.

Speciate, please

Three species of fungi most commonly cause dermatophytosis: Microsporum canis, Microsporum gypseum and Trichophyton mentagrophytes. It's not enough to determine that a patient has a dermatophyte infection. You must determine the species infecting that patient. Why? In order to provide appropriate environmental treatment, you need to know the likely source of the problem in the first place, says Ghubash. The reservoir is cats for M. canis, soil for M. gypseum and most commonly rodents for T. mentagrophytes. To determine which form of fungi you are dealing with, perform a dermatophyte culture (click here for a how-to).

Fight the long-lived M. canis

This particular species can live off the reservoir-that's the cat-in the environment for 18 months. So just treating the cat won't solve your clients' problem. Advise them that a thorough environmental treatment, consisting of vacuuming, disinfection, steam cleaning and discarding of infected bedding, is a must, says Ghubash.