Demodex

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Demodex spp.
Kingdom Animalia
Phylum Arthropoda
Class Arachnida
Sub-class Acari
Super-order Acariformes
Sub-order Prostigmata
Super-family Cheyletoidea
Family Demodecidae
Genus Demodex
Species D. canis, D. aurati, D. criceti, D. bovis

Introduction

Demodex canis - Joel Mills, Wikimedia Commons

Demodex spp. are found on all domestic mammals as well as in humans and are usually a commensal organism. It is a burrowing mite as opposed to a surface mite meaning that it penetrates into the host's tissue. Each host has a specific species of the Demodex mite. A clinical infection of Demodex spp. is termed demodicosis.

Identification

The Demodex species have a distinctive cigar shaped appearance under microscopic examination. Adults and nymphs have four pairs of stumpy legs on the anterior portion of the body, compared to larvae which only possess three pairs of legs. These species are Prostigmata, with their breathing apparatus on the anterior portion of their bodies. Prostigmata is a suborder of the class Acari containing mites with anterior breathing apparatus. This distinctive long and narrow appearance allows them to burrow into and remain inside hair follicles. The eggs are also laid into the hair follicles and look relatively long and spindle shaped.

Detection

Detecting Demodex species on animals requires the use of either a deep skin scrape or a hair pluck. These samples can then be prepared in liquid paraffin and analysed under a microscope. Adult mites, larvae and eggs may be demonstrable. Detection of a single mite is not diagnostic as they are common commensals, instead the observation of concurrent clinical signs should be used to diagnose demodicosis.

Life cycle

Demodex species complete their entire life cycle within the hair follicles and sebaceous glands of a single host. Their life cycle takes 3 weeks to complete. The female lays 20-24 eggs at a time into hair follicles. Larvae are hexapod and are the same in appearance as the adult mites during their 3 larval stages.

Transmission between hosts occurs by close contact. Usually these mites will be commensals of the host from a young age due to maternal transfer to the neonate during suckling.

Important Species

Demodex canis

This is by far the most commonly seen species of Demodex causing clinical problems. Its host species is the dog and demodicosis is usually a secondary opportunistic pathogen due to other underlying conditions.

Demodex criceti & Demodex aurati

Cause hairloss in hamsters.

Demodex bovis

Causes pea shaped nodules in cattle.

Demodex merioni

Causes hairloss in gerbils.


Demodex Learning Resources
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Cytology Q&A 18
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Literature Search
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Demodex publications


References

Forsythe, P (2007) Collection and interpretation of clinical samples for dermatological analysis In Practice 2007 29: 158-16

Henfrey, J I (1990) Canine Demodecosis In Practice 1990 12: 187-19




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