Mite Bites: Scabies, Bird Mites, and Rodent Mites

The CDC describes the most common symptoms of scabies as intense itching, especially at night, and a pimple-like skin rash. The rash typically affects the skin between the fingers and the folds at the wrists, elbows, knees and armpits, along with the penis, nipples, waist, buttocks and shoulder blades. In infants it appears on the head, face, neck, palms and soles.

Tiny burrows may be visible where the female mite tunnels just beneath the surface of the skin. University of Kentucky entomology describes the mark as a small solid bump with a red tunnel roughly 2 to 3 cm long, and puts the mite at less than 0.25 mm — smaller than a grain of sand.

The CDC notes that fewer than 10 to 15 mites may be present on an infested person who is otherwise healthy, which is why the mite is so rarely seen by the person who has it.

The CDC says that when a person is infested with scabies mites for the first time, symptoms typically take 4 to 8 weeks to develop — and that transmission can occur even before symptoms appear. Scabies spreads mainly through direct skin-to-skin contact, and less commonly through shared clothing, towels or bedding.

The CDC also describes crusted scabies as a severe form that is very contagious, and notes that delayed diagnosis and treatment of crusted scabies can often cause outbreaks.

Treatment is not a shelf purchase. The CDC states that all scabicides require a doctor's prescription and that no non-prescription products have been tested and approved to treat scabies. University of Kentucky entomology adds that severe itching can persist up to a month after treatment, so continuing itch does not automatically mean the treatment failed — that is a judgement for the clinician who prescribed it.

These are the mites behind a sudden, unexplained wave of bites indoors. University of Kentucky entomology gives the sizes: the northern fowl mite is about 0.2 mm, as small as the period at the end of a sentence; the tropical rat mite is about the thickness of a credit card, 0.03 inch; chicken or poultry mites look like a speck of black pepper at about 0.04 inch.

Bird mites get in from abandoned bird nests, pet birds or backyard poultry, and cause localised rashes and itching. Rat mites enter homes when rodent eradication displaces mites looking for new hosts, and their bites can cause irritation and sometimes painful dermatitis lasting 2 to 3 days. Poultry mites bite painfully, primarily at night, leaving small red lesions.

Control is aimed at the source: seal bird entry points and remove nests, exclude and eliminate rodents, and treat structurally rather than treating skin.

Four questions narrow it quickly.

• Is the itch worst at night, in the finger webs, wrists and skin folds, with a rash that looks like pimples? That pattern is the one the CDC associates with scabies, and it is a matter for a clinician
• Did the bites follow a clothing edge, with hard welts itching within 24 hours? See chigger bites
• Are there dark, slow-moving specks on light surfaces after a bird nest was removed or rodents were cleared? Bird and rodent mites fit
• Is the itching on the lower legs in clusters? See flea bites

University of Kentucky entomology notes that bird mites have not been found to transmit any diseases to people, and that they cannot reproduce on human blood — without a bird blood meal they die.

Mites are the usual suspect when nothing can be seen, and that is exactly when caution is needed. University of Kentucky entomology's guide to mystery bites lists environmental causes — fibres from paper, fabric, insulation and cardboard, static electricity, volatile indoor pollutants — and medical ones including pregnancy, diabetes, liver, kidney and thyroid disorders, shingles, food allergies, medications and stress. Its deciding question is whether anyone has actually seen or captured any bugs, and it advises against treating without confirmed pest presence.

Penn State Extension says the same: describe symptoms to a physician or dermatologist, try to capture a sample, and do not apply insecticides or repellents to household items, pets or yourself before you know what is going on.

If you do catch something, photograph it on a pale surface and the app identifies it. If you do not, the next step is a clinician. Nothing here is a diagnosis.