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Mite Bites

by Robert A. Barish, MD, MBA, Thomas Arnold, MD

There are multiple kinds of biting mites. Chiggers are probably the most common. Chiggers are mite larvae that are ubiquitous outdoors except in arid regions; they bite, feed in the skin, then fall off. Outside the US, chiggers may carry Rickettsia tsutsugamushi (see Scrub Typhus). They do not burrow into the skin, but because they are small, they are not readily seen on the skin surface.

Common mite species that bite and burrow into the skin include Sarcoptes scabiei , which causes scabies (see Scabies), and Demodex mites, which cause a scabies-like dermatitis (sometimes referred to as mange).

Dermatitis is caused by mites that occasionally bite humans but are ordinarily ectoparasites of birds, rodents, or pets and by mites associated with plant materials or stored food or feed.

  • Bird mites may bite people who handle live poultry or pet birds or who have birds’ nests on their homes.

  • Rodent mites from cats, dogs (especially puppies), and rabbits may bite people.

  • Swine mange mites ( S. scabiei var suis ) from pig farms or pet pigs may also bite humans.

  • The straw itch mite ( Pyemotes tritici ) is often associated with seeds, straw, hay, and other plant material; it is a parasite of soft-bodied insects that are or have been present in such materials. These mites often bite people who handle the infested items. Granary workers, people who handle grass seeds or grass hay, and people who make dried plant arrangements are most at risk.

Allergic dermatitis or grocer’s itch is caused by several species of mites associated with stored grain products, cheese, and other foods. These mites do not bite but cause allergic dermatitis because people become sensitized to allergens on the mites or their waste products.

House dust mites do not bite but feed on sloughed skin cells in pillows and mattresses and on floors (especially on carpets). They are significant because many people develop pulmonary hypersensitivity to allergens in the exoskeletons and feces of house dust mites.

Symptoms and Signs

Most bites cause some version of pruritic dermatitis; pruritus due to chigger bites is especially intense.

Diagnosis

  • Clinical evaluation

Diagnosis of nonburrowing mite bites is presumptive based on the patient’s history (eg, living, working, and recreational environments) and physical examination. The mites themselves are rarely found because they fall off after biting, the skin reaction is usually delayed, and most patients seek a physician’s assistance only after several days. Lesions caused by different mites are usually indistinguishable and may superficially resemble other skin conditions (eg, other insect bites, contact dermatitis, folliculitis).

Diagnosis of burrowing mites can often be made presumptively based on history and a scabies-like pattern of skin lesions. If the diagnosis is unclear or if treatment is ineffective, the diagnosis can be confirmed by skin biopsy.

Treatment

  • Topical corticosteroids or oral antihistamines

  • Antimicrobial therapy for burrowing mites

  • For treatment of scabies, see Scabies : Treatment

Treatment of nonburrowing mite bites is symptomatic. Topical corticosteroids or oral antihistamines are used as needed to control pruritus until the hypersensitivity reaction resolves. Through discussion of possible sources, the physician can help patients avoid repeated exposure to mites. For Demodex bites, veterinary consultation is needed.

Key Points

  • Mites that bite include chiggers (too small to see) and occasionally mites that are ectoparasites of birds, rodents, or pets and mites associated with plant materials or stored food or feed.

  • Mites that bite and burrow include Sarcoptes scabiei , which causes scabies, and Demodex mites, which cause a scabies-like dermatitis.

  • Mites that bite usually cause pruritic dermatitis.

  • Diagnose patients by history and, for burrowing mites, scabies-like pattern of skin lesions.

  • Treat symptoms (eg, topical corticosteroids or oral antihistamines for itching) and treat burrowing mite bites with antimicrobial therapy.

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