Rat mites, most commonly the tropical rat mite (Ornithonyssus bacoti), are external parasites that prefer wild or pet rodents. Infestations in human living spaces are accidental, occurring when the mites’ primary host, the rat, has died or been removed. These tiny, blood-feeding arachnids are barely visible. They seek a new host for a blood meal, often turning to humans or pets for sustenance.
Mite Survival and Host Preference
Rat mites are obligate parasites, requiring a blood meal to progress through their life cycle. They are not obligate parasites of humans and cannot establish a permanent, reproducing population on a human host. Mites will bite humans to feed, but their survival on the human body is extremely limited, typically lasting only hours after a blood meal. The human environment is fundamentally unsuitable for them.
The true concern is their survival off the host, within the home environment. Rat mites are resilient, capable of surviving for an extended period without feeding in dark, protected areas near the former host’s nest. The common estimate for persistence without a host is two to three weeks, though some reports suggest up to six weeks.
Identifying Symptoms of Infestation on Humans
The primary reaction to a rat mite bite is rat mite dermatitis. This dermatological response is caused by the mite’s saliva injected during feeding and is characterized by intensely itchy, small, red bumps. The bites often appear as papules, typically measuring 1 to 2 millimeters in diameter, sometimes resembling mosquito or chigger bites.
These skin lesions are frequently found on areas where clothing is tight or constricted, such as the waistline, ankles, or wrists. Mites tend to crawl until they meet a barrier. The intense irritation can persist for up to a week, and visible bite marks may last for three weeks. Constant scratching can lead to secondary bacterial infections.
Environmental Persistence and Source Elimination
The appearance of rat mites seeking a blood meal signals an underlying problem with a recently disrupted rodent population. Mites are driven out of their nests, often in wall voids, attics, or crawl spaces, when the primary rat host dies or abandons the area. They then migrate into the human living space, sometimes traveling several hundred feet to find a new food source.
The mites’ ability to survive for several weeks in the environment, hiding in cracks, crevices, and furniture, means that bites can continue long after the rats are gone. Eradication requires a two-pronged approach addressing both the original source and the remaining mite population. First, the rodent population must be located, removed, and entry points sealed to prevent reinfestation. Second, the environment must be treated to eliminate the thousands of mites and eggs left behind.
Treatment and Remediation
Treating the bites on the human body typically involves managing the symptoms of dermatitis. Over-the-counter anti-itch medications, such as topical corticosteroids or antihistamines, are generally used to relieve the pruritus and inflammatory reaction. For more severe reactions, a physician may prescribe stronger anti-parasitic creams or oral medications.
Eradicating the mites from the home requires professional pest control intervention. The process should include thorough vacuuming of all affected areas, especially carpets and upholstered furniture, followed by steam cleaning to kill mites and eggs. Insecticide application, often residual sprays targeted at baseboards, cracks, and crevices where mites hide, is also necessary. All bedding, clothing, and washable fabrics exposed to mites should be laundered in hot water.