Canine mange, part 1: causes and diagnosis

There are five common causes of mange in domestic dogs and these can be subdivided into surface-dwelling mites (Otodectes cynotis, Cheyletiella spp. and Neotrombicula autumnalis) and subsurface mites (Demodex spp. and Sarcoptes scabiei var canis). The historical and clinical features of the diseases that each of these mites cause, plus the best methods for their detection and diagnosis, will be considered in turn.

Otodectes cynotis (known colloquially as the ‘ear mite’) is the cause of otoacariosis or otodectic mange. This mite belongs to the family Psoroptidae and is an obligate parasite that inhabits the vertical and horizontal ear canals of dogs and cats, although other species such as ferrets can become infested. It is non-burrowing and lives on the surface of the ear canal lining. Dogs infested with Otodectes most commonly develop bilateral otitis externa, characterised by vertical and horizontal canal erythema and a dark brown, ceruminous otic exudate.

In addition to otitis externa, ectopic infestations of the head, neck, tail head and, in rare cases, the trunk can occur when mites escape the ear canals. Juvenile animals appear to be most susceptible to otoacariosis, and it is thought that older animals may acquire immunity to the mite (Powell et al, 1980).