Demodicosis

Small Animal Parasitology

Vol.18, No. 4

April 1996

Continuing Education Article

Canine Demodicosis
FOCAL POINT 5 Amitraz is the only approved
treatment for demodicosis, but daily administration of milbemycin oxime or ivermectin has recently shown promising results in amitraz-resistant cases. Louisiana State University

Stephen L. Lemarie, DVM, MS

C

anine demodicosis is thesixth most common skin disease of dogs in North America and is particularly common in the southeastern and southwestern United States.1 This article summarizes the pathogenesis and clinical features of the condition and current recommendations for diagnosis and treatment.

KEY FACTS
s Localized demodicosis usually resolves spontaneously and often requires no treatment. s Any dog with severegeneralized squamous or pustular demodicosis should be treated. s The end point for treatment of demodicosis is two consecutive negative skin scrapings. s Dogs with demodicosis and their relatives should not be bred. s Treatment should not be undertaken unless the owner agrees that the dog will be castrated or spayed when its condition improves.

MITE SPECIES Demodex mites are a specialized group ofparasitic mites that live in the hair follicles and sebaceous glands of various mammals. Although clinical dermatologic disease associated with Demodex mites has reportedly occurred in other domestic mammals, severe skin disease associated with these mites seems to be most common in dogs. The Demodex canis mite is a normal inhabitant of the skin of most dogs.2 The parasites are elongated; adultmales are 40 × 250 microns, and adult females are 40 × 300 microns.2 In addition to the adult forms, fusiform eggs, sixlegged larvae, and eight-legged nymphs are visible in skin scrapings. The entire life cycle is spent on the host and is completed in 18 to 35 days.2 A second, short-bodied species of Demodex mite reportedly occurs on dogs3 (Figure 1). The mite has been found on dogs with D. canisinfection and is believed to inhabit the superficial layers of the epidermis. This short-bodied mite resembles the short-bodied Demodex mite of cats. Transmission Demodex mites are transmitted from the bitch to nursing neonates during the first few days of life.4 In utero transmission has not been demonstrated.4 Although experimental transfer of D. canis mites to healthy dogs has been demonstrated,generalized disease does not occur and any lesions that do occur resolve spontaneously.5 Demodex canis mites desiccate rapidly outside of the hair follicle at 20˚C (68˚F) and 40% relative humidity.6 Demodicosis is not considered to be contagious between healthy adult animals. Transmission of D. canis mites to humans has not been reported. Breed Predisposition Numerous breeds have been reported tobe at increased risk of demodicosis. One study reported that shar-peis, West Highland white terriers, Scottish terriers, English bulldogs, Boston terriers, Great Danes, weimaraners, Airedale terriers, Alaskan malamutes, and Afghan hounds were the 10 breeds with the

The Compendium April 1996

Small Animal

highest statistical risk of es in dogs with generalized generalized demodicosis.7 Ademodicosis, with or withrecent retrospective study out concurrent pyoderma, found that shar-peis, Lhasa have been evaluated. ImApsos, and rottweilers were mune-complex levels in dogs overrepresented in a group with demodicosis alone of dogs with juvenile-onset were like those in control generalized demodicosis. dogs, but dogs with generalWest Highland white terriized demodicosis and pyoers,English bulldogs, Shih derma had significantly Tzus, and miniature poodles higher levels of circulating were overrepresented in a immune complexes.17 Serum IgE levels in dogs group of dogs with adultonset generalized demodico- Figure 1—Unnamed short-bodied Demodex mite that lives with generalized demodicoin the stratum corneum of dogs. sis seem to be no different sis.8 Although certain breeds from...