A Tissue Digestion Protocol for Measuring Sarcoptes scabiei (Astigmata: Sarcoptidae) Density in Skin Biopsies

Abstract

Sarcoptic mange is a parasitic skin disease caused by the burrowing mite Sarcoptes scabiei that affects a diversity of mammals, including humans, worldwide. In North America, the most commonly affected wildlife includes wild canids, such as coyotes and red foxes, and more recently American black bears in the Mid-Atlantic and Northeast United States. Currently, surveillance for sarcoptic mange in wildlife is syndromic, relying on detection of clinical signs and lesions, such as alopecia and crusting of skin. When possible, skin scrapes are used to identify the causative mite. While skin scrapes are a valuable diagnostic tool to identify mites, this approach has significant limitations when used for quantification of mite burden. To further investigate mite burden in cases of sarcoptic mange, 6-mm punch biopsies were collected from affected skin of red foxes (Vulpes vulpes Linnaeus [Carnivora: Canidae]), a species historically affected by sarcoptic mange, frequently with high mite burdens and severe skin disease, and validated on skin tissue from mange-affected American black bears (Ursus americanus Pallas [Carnivora: Ursidae]) and coyotes (Canis latrans Say [Carnivora: Canidae]). Biopsies were digested by incubating the tissue in potassium hydroxide (KOH) at 55°C. The greatest tissue clearance and lowest mite degradation resulted after 12 h of tissue digestion. The purpose of this manuscript is to describe a methodology for host tissue digestion and mite quantification in cases of sarcoptic mange. This method will provide a valuable surveillance and research tool to better understand sarcoptic mange in wild and domestic animals, with applications to a diversity of other ectoparasitic diseases.

Keywords: Sarcoptes scabiei; canid; mange; tissue digestion; wildlife.

Fig. 1.

Photograph of characteristic sarcoptic mange lesions, and from which high mite burden was identified using the KOH digestion procedure described in this paper. Biopsies were removed from these lesions for use in the high mite burden timing trials, with tissue from (a) a red fox, (b) a black bear, and (c) a coyote, all with severe lesions, alopecia, and skin crusting present.

Fig. 2.

The mean number of mites identified per individual animal from all timing trials conducted on that individual. Mites were counted in each sample at the same six time points—4, 8, 12, 16, 24, and 48 h after sample incubation began in 10% KOH solution at 55ºC. Each color represents a different individual’s mean number of mites identified from all timing trials conducted on tissue from that individual. The black line indicates the overall mean from all mites identified from all high mite burden timing trials conducted, regardless of individual or species.

Fig. 3.

Photographs of Trial P, with tissue from a black bear, at the six specified time intervals used in this study while incubated in 10% KOH at 55°C for a total of 48 h. The time series shows (a) the 6-mm biopsy before the tissue digestion trial began, (b) after 4 h of tissue incubation, (c) after 8 h, (d) after 12 h, (e) after 16 h, (f) after 24 h, and (g) after 48 h of tissue incubation.