What are Mites?
Mites are small, often microscopic organisms, and belong to the subclass Acarina (along with ticks) or the class Arachnida (along with spiders). They live in soil, water, fields, woods or houses. Some of them attack plants or animals or humans. Some do not attack (bite) humans, but can trigger allergic reaction resulting in an itchy rash. Many types of mites are harmless for human.
Types of Mites Affecting Humans
Common mites affecting humans are:
- House dust mites
- Scabies mites
- Itch mites
- Demodex mites
House Dust Mites
House dust mites (Dermatophagoides spp.) are microscopic organisms, living worldwide, all around the year, preferably in moist, poorly ventilated homes, especially on carpets, mattresses, bed lining, pillows, curtains, or on furniture. They do not live only in “dirty houses”, but they thrive readily in dust. They eat skin scales falling from people and animals, fungi, or pollens, but they do not live on the human skin, they do not bite, and they do not transfer diseases. They are harmful only to those, who are allergic to them.
Dust mites may cause or aggravate asthma, sneezing, wheezing, runny nose, or atopic dermatitis.
How to Prevent Exposure to House Dust Mites?
- Avoid having carpets, heavy curtains, soft toys and pets in bedrooms and places where you spend a lot of time
- Clean dust from all surfaces, vacuum clean carpets and floor under beds, and change and wash bed lining every week in a hot water (at least 129°F = 54°C).
- Stay away during cleaning or changing beds, since during this time and 2-3 hours thereafter, dust mites may float in the air.
- Shampoo wash or steam clean carpets at least once a year, preferably in spring.
- Prevent pollens to come into your house
- Cover bedding with mite resistant covers and use synthetic-filled pillows.
- Sensitive children should not sleep close to the floor.
- Use HEPA air filters
- Avoid using any chemicals for controlling mites, since they themselves may cause allergic reaction
Dust mites die when humidity falls under about 60%, so try to keep your home dry. Common household cleaners do not kill dust mites.
Human scabies (Sarcoptes scabiei var. hominis) are microscopic mites contracted by prolonged skin-to-skin contact with an infected person (1). Infestation through bed lining is possible, but not common. Anyone can be affected, regardless of hygiene. Scabies appear worldwide and easily spread in crowded communities, like student homes or prisons. Animals do not spread human scabies.
Mites burrow in surface layers of the skin and cause the following symptoms:
- Tiny, about 1 cm long, S-shaped skin-colored or grayish canals, and red bumpy rash appear between fingers or toes, on inner side of wrists, elbows, or knees, in armpits, over shoulder blades, around waist line, around nipples, on penis, under nails, under rings or watchbands, or anywhere on the body. The head, face, neck, palms, and soles may be affected in children and in those with low immunity, but not in otherwise healthy adults (2).
- Intense itch, that is due to allergic reaction to mites, may appear all over the body, especially at night. The person infected for the first time usually starts to itch only 2-6 weeks (up to 2 months) after infection but on subsequent infections, itch appears 1-4 days thereafter (2).
- Severe or advanced scabies (crusted or Norwegian scabies) may appear in old people or those with low immunity as moderately itching crusts. They are highly contagious both through skin contact and shared items (1).
- Staph infection may appear on sites where the skin was injured from scratching.
Diagnosis is made from symptoms or skin scraps investigated under the microscope (performed by dermatologist).
Treatment of Scabies
Scabicid topical medications such as Permetrhrin cream, or Crotamiton lotion or cream should be applied all over the body from the neck down (in children also to head and face), carefully into each body fold, according to instructions. Nails should be cut short and under-nail spaces cleaned with a tooth-pick. This should treat scabies in most cases. Itch may continue for several weeks despite successful treatment; in this case cream can be applied again after a week to be sure mites are eradicated.
Ivermectin pills are effective in both ’common’ and Norwegian scabies (4). No non-prescribed products have been approved to treat human scabies (4).
If itch at fingertips does not go away after treatment, soak fingers or toes in a warm water for some minutes until they get a ‘raisin’ appearance, and then scrap the affected skin containing dead mites away.
All individuals who were likely in skin contact with infected persons should be treated at the same time to prevent re-infection.
Itch is due to allergic reaction to mites. If itch persist after treating with Elimite Cream, antihistamines, or steroids by mouth can be taken until necessary.
Prevention of Scabies
To prevent scabies, avoid skin-to-skin contact with infected persons.
If you have had scabies, wash your clothes, bed lining and towels used in last three days to prevent re-infection. Clothes that cannot be washed may be sealed for at least 72 hours – all scabies mites or their eggs should die in this time. Thorough cleaning of your living place is not required, though, except in Norwegian scabies.
Chiggers (Eutrombicula spp.) are about 1 mm sized, red, hairy mites found in grass or woods. They bite human (or animal) skin and spill saliva into it and then eat dissolved skin particles (5). It is this saliva that causes itchy red welts on the areas with a thin skin, mostly around the ankles, behind the knees or elbows and around the waist line.
Chiggers bites may be prevented by using insect repellents and wearing pants and long-sleeved shirts. Even slight rubbing or washing removes chiggers.
Picture: Chigger bites
Human Demodex Mites
Human Demodex mites live mainly in oil (sebaceus) glands and hair follicles of eyebrows and eyelashes (but may be found in hair follicles elsewhere on the body). Demodex mites are often present in hair follicles of healthy people without causing any symptoms, but they may cause itchy eyes or itchy eyelids. Other symptoms may include:
- Eyelid scaling or redness
- Loss of lashes
- Dry or red eyes
- Blurred vision
Diagnosis may be made by finding mites on pulled eyelashes under the microscope. Finding Demodex mites can be a coincidence, though, since they live in the hair follicles of many healthy people.
Therapy includes (8):
- Luring eyelid margin with ether, proparacaine and 70% alcohol (in doctor’s office) weekly for three weeks
- Scrubbing eyelids with diluted baby shampoo (50% water, 50% shampoo) twice daily, and applying prescribed antibiotic ointment overnight
- Another regime includes tea tree oil and Macadamia nut oil
- Discard used eyelid/eyebrow makeup, and do not use makeup during treatment
- Clean bed sheets
- Other family members have to be checked
- Pets have to be checked (type of Demodex mites that live on dogs is rarely found in human, though)
- Who is at risk to get scabies? (cdc.gov)
- Symptoms of scabies (cdc.gov)
- Scabies treatment (cdc.gov)
- Medications for scabies (cdc.gov)
- Chiggers (ohioline.osu.edu)
- House dust mites (dermnetnz.org)
- House dust mites (lancaster.unl.edu)
- Demodex mites treatment (emedicine.medscape.com)
Article reviewed by Dr. Greg. Last updated on April 23, 2011