Acariasis (Mite and Tick Infestation)

What acariasis means

The word comes from Acari, the scientific group that includes mites and ticks. "Acariasis" (also spelled acarinosis) covers any disease caused by them in people or animals. In humans it mostly means skin problems, either from mites living in the skin or from mites and ticks biting it.

There are two broad patterns:

• Infestation: the mite lives and breeds in human skin. Scabies and Demodex are examples.
• Bites and dermatitis: the mite or tick bites and then leaves or dies. The skin reacts with itchy bumps. Chiggers, bird mites, rodent mites and grain or straw itch mites cause this.

House dust mites are related, but they do not bite or live on skin. They cause allergies such as asthma, eczema flares and allergic rhinitis rather than acariasis.

Types of acariasis

Symptoms

Itching is the main symptom of nearly every type. Other signs depend on the mite:

• Scabies: small red bumps and scratch marks, and fine gray or skin-colored wavy lines a few millimeters long (burrows). Itching is worst at night. In a first infestation, it begins 2 to 6 weeks after contact, because the itch is an allergic reaction to the mites and their eggs. In a repeat infestation, it starts within 1 to 4 days. Men can get very itchy nodules on the penis and scrotum. Babies may have it on the palms, soles, face and scalp.
• Chiggers: intensely itchy red bumps, sometimes with a central blister, clustered where clothing is tight. The larvae fall off after feeding, so they are not found in the skin. Itching peaks at 1 to 2 days and the bumps last 1 to 2 weeks.
• Bird or rodent mites: itchy bites that keep appearing at home, sometimes with tiny moving specks visible on skin or bedding.
• Demodex: redness, small pustules and roughness on the cheeks and nose, or crusty eyelash bases (Demodex blepharitis).
• Ticks: usually painless. You may find the tick itself, or a small red bump after it falls off.

Scratching can break the skin and let bacteria in, causing impetigo or cellulitis.

Causes and how it spreads

Scabies spreads mainly by prolonged skin-to-skin contact, such as between family members, sexual partners and in nursing homes, child care and prisons. A brief handshake rarely spreads it. Mites survive off the body for only 2 to 3 days, so bedding and clothing are a minor route, except with crusted scabies.

Chiggers, ticks and outdoor mites come from the environment: long grass, woodland, gardens, animal nests and stored grain. They do not pass from person to person.

Diagnosis

A doctor diagnoses most acariasis from the pattern of the rash and your history: who else is itching, where you have been, and whether you have pets, birds nesting nearby, or have been in long grass.

For suspected scabies, a clinician may:

• look closely at the skin with a magnifying dermatoscope to spot the mite at the end of a burrow
• gently scrape a burrow and look for mites, eggs or mite droppings under a microscope
• use the "ink test", rubbing ink over a suspicious area and wiping it off, which leaves burrows outlined

A negative scraping does not rule scabies out, so treatment is often given on clinical grounds. Rashes that look similar include atopic dermatitis, contact dermatitis, insect bites, hives and lice infestation (pediculosis).

Treatment

Scabies

• Permethrin 5% cream: applied from the neck down (including the scalp and face in young children and older adults) and washed off after 8 to 14 hours. A second application 7 days later is commonly advised.
• Oral ivermectin: tablets, usually two doses a week or more apart, often used for outbreaks, crusted scabies or when creams are impractical.
• Treat everyone at once: all household members and close contacts should be treated on the same day, even if they have no symptoms.
• Wash bedding and clothing used in the past 3 days in hot water and dry on a hot cycle, or seal items in a plastic bag for at least 72 hours.

Itching often continues for 2 to 4 weeks after successful treatment, because the skin is still reacting to dead mites. This is not a sign of failure. New burrows or new bumps after 2 to 4 weeks suggest re-infestation or treatment failure.

Chigger, bird and rodent mite bites

These mites do not stay in the skin, so no mite-killing treatment is needed for the person. Wash the skin with soap and water, and treat the itch with cool compresses, calamine lotion, an over-the-counter hydrocortisone cream and a non-drowsy antihistamine, following the label. For bird or rodent mites, the nest must be removed and the area treated, or the bites keep coming.

Demodex

Doctors use topical ivermectin or metronidazole for facial demodicosis, and tea tree oil-based eyelid cleansers or prescription eye drops for Demodex blepharitis.

Ticks

Remove an attached tick as soon as possible with fine-tipped tweezers. Grasp it close to the skin and pull upward with steady pressure, without twisting. Clean the area. Watch the site for 30 days for a spreading rash or fever, which could mean Lyme disease or another tick-borne infection.

Prevention

• Avoid prolonged skin contact and sharing bedding with someone who has scabies until they are treated.
• In grassy or wooded areas, wear long trousers tucked into socks and use a repellent containing DEET or picaridin on skin, or permethrin on clothing.
• Shower within 2 hours of coming indoors and check the whole body for ticks.
• Remove bird and rodent nests from attics, eaves and air vents.

Frequently asked questions

What is acariasis?

Acariasis is any infestation or skin disease caused by mites or ticks. Scabies, chigger bites, bird mite bites, Demodex overgrowth and tick infestation all count. The common feature is an itchy rash. Treatment depends on the type of mite.

Is acariasis contagious?

Only some forms. Scabies spreads through close skin-to-skin contact, and crusted scabies spreads very easily. Chiggers, ticks, bird mites and grain mites come from the environment and do not spread from one person to another.

How do I know if I have mites on my skin?

Suspect scabies if you have intense night-time itching with bumps between the fingers, on the wrists, waist or genitals, and others close to you are itchy too. Bites around the ankles and waistband after outdoor activity suggest chiggers. A doctor can confirm it by examining a skin scraping.

Why do I still itch after scabies treatment?

Itching can last 2 to 4 weeks after the mites are dead, because your immune system is still reacting to their remains. Moisturizers, cool compresses and antihistamines help. If new burrows or bumps appear after 2 to 4 weeks, see your doctor about re-treatment.

Are house dust mites a cause of acariasis?

No. House dust mites do not bite or live on people. They cause allergic problems such as asthma, eczema flares and allergic rhinitis. Reducing dust, using allergen-proof bedding covers and washing bedding in hot water helps.