Microbiology Case Study: 92-year-old with Itchy Rash

A 92 year old female nursing home resident presented to her primary care physician with an itchy rash between her fingers and at her waist. A skin scrape revealed the following:

Sarcoptes scabiei  (the itch mite) from skin scraping.
Sarcoptes scabiei (the itch mite) from skin scraping.

Laboratory identification:

It is critical that an appropriate specimen is collected for identification of the organism. A fresh unopened papule on the skin should be selected for skin scraping. A scalpel coated in mineral oil should be used to vigorously scrape the papule and transfer the scrapings to a glass slide. A well collected skin scraping draws blood.

Female mites are 330-450 microns long; males are slightly smaller at 200-240. The eggs are thin shelled and approximately 150 x 100 microns in size. It is also possible to see fecal pellets in scrape specimens.


Sarcoptes scabiei is transmitted by direct contact. The gravid female mite burrows into the epidermis leaving behind a trail of up to 40 eggs. The burrowing process is enhanced by the presence of suckers and specialized cutting surfaces on the organism. The larvae hatch in 3-4 days, leave the burrow, and reach adulthood in hair follicles. The typical patient presentation is intense pruritis, often in folds of skin, with possible secondary bacterial infection due to itching and excoriation.

Scabies is treated with aqueous solutions of malathion or permethrin.

-Lauren Pearson, D.O. is a 2nd year anatomic and clinical pathology resident at the University of Vermont Medical Center.


-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.

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