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 what the best diagnostic technique is.

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 type 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.

So 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 of 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 new technique, relatively new, in which we use a magnified lens, essentially, to magnify the visualization of the skin and you can see specific alterations of the hair associated with dermatophytosis.

And again, as I said earlier, the best diagnostic methodology is a fungal culture. So 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 also requires up to 3 weeks to kind of 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.