1. Sarcoptes scabiei

2. Taxonomic classification
Class Arachnida
Sarcoptes scabiei (sarcoptic mange mite, itch mite)

3. Host spectrum
Domestic (sheep, goats, cattle, pigs, equids, dogs , rabbits) and wild animals, humans, other primates
Each host is considered to have its own strain or variety, e.g. Sarcoptes scabiei var. equi and Sarcoptes scabiei var. hominis

4. Geographic distribution
Probably worldwide

5. Morphology
Adults - rounded body; females mm long and mm wide, males mm long, mm wide; 8 short legs, posterior 2 pairs do not extend beyond the body margin; unsegmented pedicels; mouthparts have a rounded appearance.

7. Sarcoptes scabiei, the scabies or itch mite

9. Life cycle (stages)
Female mites tunnel into the epidermis , lay 3-5 eggs per day for a total of eggs
Six-legged larvae hatch from eggs
Larvae and nymphs burrow into the stratum corneum and form pockets where they molt and feed
Adult males and females develop and mate
Life cycle requires 2-3 weeks to complete

12. Transmission: General
Highly contagious
Close contact often required
General life cycle
Females lay eggs on host or in environment
Egg hatches into larva
Larva  nymph  adult
Direct contact with susceptible host
All of the acariases are highly contagious for susceptible species. Close contact may be required if the mites are few and do not survive well in the environment (e.g. some forms of sarcoptic mange), but transmission occurs readily if large numbers of mites are present. Animals with sub-clinical infestations can also spread mites. Female mites lay their eggs either on the host or in the environment. The egg hatches into a larva, which generally passes through two nymphal stages to become an adult. All of the mites that cause acariasis are transmitted by direct contact. The importance of fomites in transmission varies with the species of mite and its survival in the environment.
Center for Food Security and Public Health, Iowa State University, 2012

14. Site of infestation
Skin (epidermis); females, eggs, larvae and nymphs in tunnels or pockets, males on the skin surface.

15. Human Scabies Severe pruritus Norwegian scabies Especially at night
Papular rash or nodules
Burrows pathognomonic
Secondary infections possible
Norwegian scabies
Severe form found in immunocompromised people
The most prominent symptom of human scabies (Sarcoptes scabiei var hominis) is severe pruritus, particularly at night. The head and neck are usually spared, except in infants and young children. There may also be a papular rash, particularly on the shoulder blades, webbed spaces of the fingers, feet, belt line, scrotum, penis, breast, or the folds of the wrist, elbow or knee. Pink, red, tan or brown nodules, ranging in size from 2-20 mm, may also be seen. Burrows (thin, slightly elevated, pinkish-white or grayish-brown, 2-5 mm long straight or curved lines) are pathognomonic. A dot at one end of the burrow indicates the presence of a mite. Complications may include secondary bacterial infections. A more severe form of scabies (Norwegian or crusted scabies) is found sometimes in immunocompromised persons, the elderly, and mentally incompetent individuals. In this form, there are large numbers of mites, discrete vesicles and extensive thick crusts on the skin, but pruritus may be slight or absent. Nail dystrophy and scalp lesions may also be seen. Secondary lesions, the result of scratching, may include scratches, generalized eczematous dermatitis, erythroderma (generalized exfoliative dermatitis) and hyperpigmentation.
[This photo shows a human hand with Sarcoptes scabiei var. hominis infestation. Source: CDC Public Health Image Library.]
Center for Food Security and Public Health, Iowa State University, 2012

16. SIGNS and SYMPTOMS scabies rash
Classical sites of scabies rash...
between fingers
wrists
auxiliary areas
female breasts (particularly the skin of the nipples)
the umbilical area
penis and scrotum
buttocks
inside of legs
ankles

17. Pathogenesis/clinical signs
Initial lesions occur on the hand, elbows, axillary or inguinal regions
Lesions are initially erythematous, then become papular; papules rupture and skin becomes crusty
Alopecia, thickening of the skin, pruritus
Secondary bacterial infection, allergic reaction, self-mutilation may occur

18. Tissue section

20. A severe case of scabies of the hand.

21. Crusted appearance on hands

22. Diagnosis
Skin scraping
ink test

23. Treatment
Lindane shampoo or dip, phosmet (ParamiteR), or Amitraz (MitabanR)
ivermectin weekly for four weeks orally or subcutaneously

24. Public health significance
Humans may be infested with the strains from animals and these infestations may be mild to intensely pruritic, but they are self-limiting.