Demodex

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. They have four pairs of stumpy legs on the anterior portion of the body.These species are prostigmata, with their breathing apparatus on the anterior portion of their bodies. This distinctive long and narrow appearance allows them to burrow into and remain inside hair follicles.

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. 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. Transmission between hosts occurs by close contact usually these will be commensals of the host from a young age due to maternal transfer to the neonate during suckling. Their life cycle takes 3 weeks to complete.
Eggs

• 20-24 laid at a time into hair follicles.

Larvae

• Hexapod
• 3 larval stages before becoming adult

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 hair loss in Hamsters.

• Demodex bovis

Causes pea shaped nodules in cattle.