Itch Mites

Sarcoptes scabiei

Scabies is caused by a parasitic arthropod, the itch mite (sarcoptes scabiei). Itch mites belong to the class of arachnids with 8 legs. Similar to lice, scabies spreads primarily where many people live closely together. Therefore, retirement and nursing homes, but also kindergartens, schools and even hospitals are most frequently affected. Scabies is spread from humans to humans through close skin-to-skin contact. The incubation period for scabies is about 3-6 weeks. With an intact immune system and with good hygienic conditions, the immune reaction of the body keeps the number of mites at a relatively low level. After infestation, the 0.3 to 0.5 mm long females burrow just beneath the surface of the skin and deposit their eggs in the so-called burrows. Males remain on the surface of the skin to find a female. The lifespan of a female mite living in the skin is about 60 days. Off a person, itch mites usually no not survive more than 48 hours, as they feed on human skin cells and lymphatic fluids.

Clinic

Itch mites prefer skin areas with a higher body temperature. Therefore, they most commonly occur between fingers, on wrists, genitals, armpits and belly buttons. In small children or in case of a serious clinical picture, the scabies norvegica, mites may also burrow into the neck and/or head. In the first weeks, the infestation may be asymptomatic and may lead to strong itching at night due to an immune reaction against mite products (decayed mite components, eggs, faeces).

Diagnosis with the help of dermatoscopy

Very important for the diagnosis are the anamnesis (especially nocturnal itching, possible infestation of close roommates or colleagues) and the examination of the typical preferred localisations such as between fingers and on genitals. Scratching will show little red bumps or sometimes even red burrow lines, which look like long-stretched tracks. In former days, a biopsy was necessary in order to diagnose in infestation.

Further developments in dermatoscopy (e.g. improved image sharpness and magnification) have made the diagnosis of scabies a lot easier. In a diagnosis with the help of a dermatoscope the itch mites can be found and seen a lot easier and a long search is not necessary anymore. Usually, they can be found on the edge of a bump or a burrow. The head and the breast of the mite appear typically as dark triangle-shaped areal. The abdomen is transparent and therefore hardly visible. 

Therapy

Permethrin is used to treat scabies in adults and children for external application. Alternatively benzyl benzoate can be used. Oral ivermectin is also used occasionally. Usually, a short term after treatment with a mild steroid cream is recommended.

During the treatment, all objects that are also used by other persons should be cleaned and disinfected in order to prevent transmission of scabies. Clothes and bed linen should be washed at a temperature of at least 60° C. Alternatively, place the clothes in a hermetically sealed plastic bag and freeze it for a few days.

For further information please use the Scabies Diagnostic information.

Sources

Videodermoscopy compared to reflectance confocal microscopy for the diagnosis of scabies. Cinotti E, Labeille B, Cambazard F, Biron AC, Chol C, Leclerq A, Jaffelin C, Perrot JL. See comment in PubMed Commons belowJ Eur Acad Dermatol Venereol. 2016 Sep;30(9):1573-7. doi: 10.1111/jdv.13676. Epub 2016 May 11

Diagnosis of trombiculosis by videodermatoscopy. Nasca MR, Lacarrubba F, Micali G. Emerg Infect Dis. 2014 Jun;20(6):1059-60. doi: 10.3201/eid2006.130767.

Dermoscopy aids the diagnosis of crusted scabies in an erythrodermic patient. Bollea Garlatti LA, Torre AC, Bollea Garlatti ML, Galimberti RL, Argenziano G. J Am Acad Dermatol. 2015 Sep;73(3):e93-5. doi: 10.1016/j.jaad.2015.04.061