Deep skin scrapings are necessary to find the deep follicular dwellers Demodex canis and D. cati mites.
The skin should be squeezed before and/or during the scraping.
A new (or clean dulled) scalpel blade dipped in mineral oil is scraped in the direction of hair growth until slight dermal bleeding is observed.
At least 3 sites should be sampled if multiple areas are affected.
Droplets of blood should be seen microscopically if the scrapings are of adequate depth however they should be smeared thin enough to examine.
An additional way to look for Demodex is with a trichogram. In KMnO4, however, the mites can digest and also if transportation is too long to a cytologist they can even disappear in liquid paraffin!
Nymphs are smaller but most are adults with 8 legs and segmented and about. In the canine Demodex species, the length of adult mites ranges from 180 to 210 µm for D. canis, 330 to 370 µm for D. injai, and 90 to 140 µm for the unnamed species. In the feline Demodex species, the length of adult mites ranges from 181 to 219 µm for D. cati and 81 to 115 µm for Demodex gatoi.
Finding Demodex species on scrape should always be regarded as suspicious especially if more than one is harvested even though low numbers are present in the skin as commensal parasites.
First published: Wed, Jan 12 2011