What are Mites?

Mites are small, often microscopic organisms, belong to the subclass Acarina (along with ticks) and the class Arachnida (along with spiders). They may live in soil, water, fields, woods, or in houses. Some of them attack plants, some animals, some humans, some don’t attack humans, but can trigger allergic reaction, and many of them are harmless for human.

Types of Mites Affecting Humans

Common mites affecting humans are:

  • House dust mites
  • Scabies mites
  • Chiggers
  • 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 don’t 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 don’t live on the human skin, they don’t bite, and they don’t 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 54°C).
  • During cleaning, or changing beds, and 2-3 hours thereafter, dust mites may float in the air, so all sensitive persons should stay away during this time.
  • 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 may cause allergy to sensitive persons

Dust mites dye when humidity falls under about 60%, so try to keep home dry. Common household cleaners do not kill dust mites.

Diagnosis of allergy to house dust mites is made by allergist.

Scabies Mites

Human scabies (Sarcoptes scabiei var.hominis) are microscopic mites contracted by prolonged skin-to-skin contact with 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 (student homes, prisons, etc.) 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 who was infected for the first time usually start to itch only 2-6 weeks (up to 2 months) after infection but on subsequent infections, itch appears 1-4 days after (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 via skin contact and shared items (1).
  • Staph infection may appear on the sites where skin was injured from scratching.

Diagnosis is made from symptoms, or, if necessary, scraps from affected skin may be investigated under the microscope for mites.

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. Since itching continues for several weeks despite successful treatment, cream can be applied again after a week to be sure mites are eradicated.

Ivermectin pills are effective in “common”, and Norwegian scabies (4). No non-prescribed products have been approved to treat human scabies (4).

If itching at fingertips doesn’t go away after treatment, fingers (or toes) may be soaked in a warm water for some minutes until they get a “raisin” appearance, then affected skin with dead mites can be scrapped away.

All persons who were likely in skin contact with infected persons should be treated at the same time to prevent re-infection.

Itching is due to allergic reaction to mites. If itching persist after treating with Elimite Cream, antihistamines, or steroids by mouth can be taken until necessary.

Prevention of Scabies

Someone who don’t want contract scabies, should avoid skin-to-skin contact with infected person.

Someone who has had scabies, should wash clothes, bed lining, and towels, used in last three days to prevent re-infection. Clothes that can’t be washed may be sealed for at least 72 hours – all scabies mites or their eggs should dye in this time. Thorough cleaning of a living place is not needed, except in Norwegian scabies.

Chiggers

Chiggers (Eutrombicula spp.) are about 1 millimeter 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 mass (5). It is this saliva that causes itchy red welts on the areas with thin skin, mostly around ankles, behind knees or elbows, and around 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 is with checking an eyelash under the microscope – organisms may be seen.

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

Prevention:

  • Eyelid/eyebrow makeup has to be discarded, and makeup not used during treatment
  • Bed sheets have to be cleaned
  • 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)

Further Reading:

Itchy Rash

References:

  1. Who is at risk to get scabies? (cdc.gov/scabies/risk)
  2. Symptoms of scabies (cdc.gov/scabies/symptoms)
  3. Scabies treatment (cdc.gov/scabies/treatment)
  4. Medications for scabies (cdc.gov/scabies/hcp/meds)
  5. Chiggers (ohioline.osu.edu)
  6. House dust mites (dermnetnz.org)
  7. House dust mites (lancaster.unl.edu)
  8. Demodex mites treatment (emedicine.medscape.com)