Diagnostic tests for identifying dermatophytes

In this interview with dvm360, Domenico Santoro, DVM, MS, DrSc, PhD, DACVD, DECVD, DACVM, offers an overview of the various diagnostic tests available for dermatophytosis, a common fungal infection in cats and dogs. In the video, Santoro discusses some pros and cons of each test and explains which diagnostic technique is the best.

Below is a partial transcript, lightly edited for clarity.

Domenico Santoro, DVM, MS, DrSc, PhD, DACVD, DECVD, DACVM: One of the common fungal infections is dermatophytosis, and with dermatophytes, there are different types of tests that we can do. The simplest test is called Wood lamp, which is a very sensitive test but not very specific, followed by hair plucking and trichography.

Trichography essentially implies that the veterinarian will take [a] hair sample, look at the microscope, and look for alterations of the hair shaft. This test is very specific, but contrary [to] the wood lamp, it’s not really sensitive because it depends [on whether] we collect the affected hair or not.

Then there is a dermoscopy, which is a [relatively] new technique...in which we use a magnified lens...to magnify the visualization of the skin, and you can see specific alterations of the hair associated with dermatophytosis.

And...as I said earlier, the best diagnostic methodology is a fungal culture. A fungal culture [involves] the collection of hair, specifically the periphery of the lesion, and putting this hair or scales—or whatever material we have—in a culture medium and submitting it to the microbiology laboratory. This test is the best in terms of specificity and sensitivity, but [it] requires up to 3 weeks to specifically isolate the organism.

Once the organism has grown and is present in the culture, the culture has to be followed by a microscopic identification of the organism. So the microbiologist will specifically look at what type of morphology the organism has to identify the genus of the species of the fungus.