Team tips from CVC: Tricks to help uncover feline dermatophytosis
Identifying dermatophytosis in cats starts with a high degree of suspicion, as it can mimic most other skin diseases, says Karen Moriello, DVM, DACVD, speaking at CVC San Diego. Dr. Moriello offered tips for technicians and veterinarians to help detect primary fungal pathogens such as Microsporum canis.
Select hairs that glow apple-green under a warmed-up Wood's lamp for direct microscopic examination. You can also hold the Wood's lamp to the side of the microscope stage to help locate the infected hairs on the slide.
Potassium hydroxide isn't required, you can use mineral oil to examine the slide, and infected hairs can be easily identified through the 4X or 10X objective.
Finding infected hairs allows initiation of immediate aggressive therapy, but fungal culture is still recommended to confirm a diagnosis.
To collect samples for fungal culture, use a new toothbrush and swipe areas of suspect lesions 20 times. Hairs should be present in the brush. Place the brush head-first into a plastic sandwich bag to contain any spores-- don't carry the toothbrush in the open. When you take the toothbrush out of the bag, hold it over a Clorox wipe.
Also hold the culture plate upside down over a Clorox wipe while you inoculate the medium with the toothbrush sample. Gently stab the bristles into the medium, starting in the center and working outward.
Label the plates, and if you incubate them in-house, place each plate medium-side up in a small sandwich bag and keep the plates in a clear plastic shoe box with a lid. The box doesn't have to be kept in the dark, but the temperature should be maintained between 75 F and 80 F.
Examine the plates daily and record details of the gross findings. Pale, nonpigmented colonies that turn dermatophyte test medium red are suspect, but are not diagnostic, for dermatophytosis. Obtain a sample of a suspect colony with Scotch tape and use microscopic examination to definitively identify the organism.