Notes from the veterinary webinar Demodicosis veterinary CPD from The Webinar Vet

Demodicosis is a reasonably common inflammatory, parasitic disease of dogs characterised by the presence of larger than usual numbers of demodectic mites. The initial proliferation of the mites may be due to a genetic or immunological disorder. Mites can be found in young and older dogs. Most dogs have some demodex mites but in some individuals these mites multiply in their thousands to cause erythema and alopecia. The mites most commonly live in the hair follicles(Demodexcanis) although, a short stubby mite recognised as a separate species lives in the stratum corneum. The demodex mite spends all of its life in the skin and is very rarely believed to be contagious. Demodex is spread from mum to pup during lactation over the muzzle and face. Mites have been found puppy hair follicles within 16 hours. In the majority of cases these mites do not cause a problem but in some cases may develop into disease. The pathogenesis is not clearly understood. In the early part of the last century, it was believed that the demodex mite acted as a transmitter of staphylococcal infection in the dog. Another researcher reported the development of generalised demodicosis in pups receiving anti-lymphocyte serum. Danny Scott hypothesized that dogs with generalised demodicosis have a specific T-cell deficit. This allows the multiplication of the mites which then induce a serum immunosuppressive factor which causes generalised T-cell suppression. As the mites are eradicated, measurable T-cell suppression disappears. There are 2 forms of demodectic mange 1. localised 2. generalised Localised is the most common form and is seen in young dogs under a year old. It is often seen on the face or around the eyes and manifests itself as small patches of alopecia. It is usually not pruritic. If there are more than 12 areas of alopecia then it is almost certainly generalised, less than 6 and it is localised. Dogs in the middle have to evaluated on an individual basis. If a dog has localised demodex I usually do not feel that it is necessary to treat them. A small percentage of these will go on to develop generalised disease. In generalised disease, large areas of the body can be affected. There is usually a secondary pyoderma and the dog may be itchy. This pyoderma may develop into a deep infection requiring long term antibiosis. Staph pseudintermedius and the demodex mite share a symbiotic relationship and treating just the bacteria may lead to a big improvement but once stopped the condition will often flare quickly. Scale and comedones can occur. The dog is often erythematous and alopecic. Some dogs may only have mites in their feet. This is still classed as generalised disease. Skin scraping may miss the mites and the dog is misdiagnosed as having only a bacterial infection. Biopsies are sometimes necessary in these cases to rule demodex in or out.