Introduction

Ringworm in domestic dogs is probably over-diagnosed, especially when a presumptive diagnosis is made based only on observable signs. However, using one or more of several readily available in-house tests, most veterinarians will come up with an accurate assessment of the dog’s condition.

How Ringworm is Diagnosed

When presented with a dog showing symptoms of circular, patchy hair loss, a veterinarian will first take a thorough history and perform a complete physical examination. There are several more advance diagnostic tools available to confirm a diagnosis of ringworm. One of those tools is a trichogram, which involves plucking hairs from the edge of one of the patchy lesions and immersing them in oil or potassium hydroxide mixed with Indian ink to look for evidence of fungal spores. Alternatively, the area of hair loss can be examined under an instrument called a Wood’s lamp, which emits a certain wavelength of ultraviolet light that causes roughly 50% of the strains of Microsporum canis to fluoresce an apple-green color. Unfortunately, a number of other substances also fluoresce under a Wood’s lamp, which can cause false positive test results.

Fungi can also be cultured (grown in a laboratory) using specific dermatophyte (fungal) test media that change color in the presence of ringworm growth. Samples can also be examined microscopically, using special stains to identify the presence of fungal organisms.

Special Notes

Veterinary and laboratory personnel should use caution when taking and assessing samples from suspected ringworm lesions, to prevent the chance of contagion. Owners should also use extreme care if they suspect ringworm and should avoid touching circular or oval areas of patchy hair loss on their dogs without wearing rubber or latex gloves.