Current Advice on Parasite Control:
Ectoparasites - Sarcoptic Mite
Sarcoptes scabiei (canine mange mite, itch mite)
Different varieties of Sarcoptes scabiei infest a wide range of mammalian hosts, including dogs and other canids, human beings, horses, and cattle; cats are rarely infested with this mite. In all hosts, mites tunnel in the epidermis and produce an intensely pruritic dermatitis with hyperkeratosis and alopecia. Infestations between hosts occur, but the mites tend not to survive for long on hosts other than those to which they are adapted; thus, they are considered host-adapted strains of a single species rather than distinct species.
Overview of Life Cycle
- o Mites live in burrows in the skin where the female glues her eggs to the tunnel walls. Eggs hatch to produce six-legged larvae that molt to become first- and second-stage nymphs before becoming adults.
- Eggs are large (about 230 μm long) and ellipsoid.
- Adults are approximately 300-500 μm long. The first two pairs of legs of the eight-legged adult females end in long and unsegmented stalks (pedicels) that end in a wineglass-shaped caruncle; the third and fourth pairs of legs end in long setae. Male mites have setae only on the third pair of legs, with pedicels and caruncles on the other legs. Males also have marked thickening of the cuticle between the various plates on the ventral surface that appear dark, compared with the rest of the body. The dorsal surface of both the male and female mites is covered with large triangular spines (most conspicuous in the female).
- Infestations typically produce hyperkeratosis and alopecia.
- Lesions become highly pruritic and are often the cause of self mutilation. Lesions may become bloody from the scratching of the affected dog.
- Mites typically are found on the margins of the ears, lateral elbows, and lateral hocksof affected animals, although lesions are also common on the flanks and ventrum, especially in more severe cases.
- Sarcoptic mange is among the most commonly diagnosed skin diseases in dogs examined in teaching hospitals.
- Severe skin disease may be present even though repeated skin scrapings recover no mites.
- Infestations appear to occur throughout the range of the dog and are present in both cool and tropical climates.
Host Associations and Transmission Between Hosts
- This mite appears to be restricted to the dog but can be spread between canids rather freely. Sarcoptes scabiei is a serious parasite of red fox (Vulpes vulpes) and coyotes (Canis latrans), which could perhaps be considered reservoir hosts in some areas.
Prepatent Period and Environmental Factors
- Mites develop from eggs to egg-producing adults in approximately 3 weeks.
- Sarcoptes scabiei does not survive in the environment off the host; infestations are dependent upon direct contact between animals or fairly immediate fomite transmission, such as by clipper blades.
Site of Infection and Pathogenesis
- Mites are found in burrows in the skin.
- Lesions typically are noted on the margins of the ears, lateral elbows, lateral hocks of infested animals. Occasionally pododermatitis also develops.
- Infestations initially produce dry, crusted lesions that become pruritic and on excoriation often develop a serous exudate. Alopecia is usually present as well.
- Some dogs develop a severe form of sarcoptic mange referred to as “crusted scabies” in which large mite populations are present within profound hyperkeratosis.
- Skin scrapings for sarcoptic mange mites should be deep enough to examine the full thickness of the epidermis and produce a sample that is tinged with blood.
- Often it is helpful to dip the scraping scalpel in mineral oil and tease apart the scrapings on the microscope slide with needles, especially when significant hyperakeratosis is present.
- Mites and their eggs will be clearly visible at the lowest power of the compound microscope.
- If no mites are seen but lesions strongly suggest sarcoptic mange, response to treatment may be used to reach a clinical diagnosis.
- Selamectin is labeled for treatment of sarcoptic mange in dogs. Topical moxidectin is labeled for treatment of S. scabiei in dogs in Europe but not in the United States.
- Fipronil and flumethrin/imidacloprid collars are labeled as “aids in control of sarcoptic mange” and “aids in the treatment and control of sarcoptic mange” respectively. Off-label, high dose ivermectin has also been used historically but may cause toxicity in dogs with the MDR1 mutation and failures have been reported.
Control and Prevention
- Routine use of fipronil, topical moxidectin, or selamectin likely will prevent infestations with Sarcoptes scabiei in dogs.
Public Health Considerations
- People can develop a self-limiting infestation with S. scabiei from dogs. The lesions that are produced will be highly pruritic but usually clear without the need for specific treatment for the mite infestation. If lesions persist or are particularly uncomfortable, a dermatologist should be consulted.
- People also develop infestations with Sarcoptes scabieie var. hominis following contact with other infested people. Dogs are not always the source of human scabies, particularly when institutional outbreaks occur.
- Human scabies is considered a sexually transmitted disease although any close contact between individuals may facilitate transfer of mites and establishment of a new infestation.
- Currier RW, et al., 2011. Scabies in animals and humans: history, evolutionary perspectives, and modern clinical management. Ann NY Acad Sci. 1230:E50-60.