"Bird mites" or "Tropical fowl mites" are the common names used to describe the mite Ornithonyssus bursa from the family of mites Macronyssidae; these mites are often incorrectly called bird lice, particularly within the pest control industry, and are also commonly the cause of paper mite problems (strictly speaking there are no such things as paper mites). This species of bird mite is widely distributed throughout warmer regions of the world. The mites are haematophagous (feed on blood) natural parasites of common birds including pigeons, starlings, sparrows, Indian mynahs, poultry, and some wild birds. Ornithonyssus bursa mites are small with eight legs, barely visible to the eye, oval in shape with a sparse covering of short hairs, and are extremely mobile. They are semi-transparent in colour which makes them difficult to detect on skin until blood is ingested and then digested - when they may appear reddish to blackish.

Contact with humans occurs after the birds gain entry through unprotected eaves, or to roof cavities via broken tiles to construct their nests in homes, factories, barns and other dwellings in early spring or summer. The large amounts of nesting material used by the birds provide the mites with an ideal environment in which to thrive. The unfeathered nestlings plus the adult birds occupying the nest are utilised as a ready blood source for the expanding population of mites. When the young birds are ready to fledge, some mites remain attached to the feathers of their bird hosts and feed intermittently. The mites remaining in the abandoned nest, and left without a suitable host when the birds leave or die, will roam and disperse throughout the dwelling over a 1-2 week period searching for new hosts. Most mites will die within 10 days without a blood meal from a bird host. They will bite but cannot survive on humans and do not infect/infest human skin.

Clinical Presentation

Bites from these mites are difficult to diagnose and can be sometimes mistaken for flea bites although they are typically smaller and less florid. Although the effect of a bird mite invasion is temporary, the mites can cause severe irritation, rashes and intense itching from the saliva they inject while biting, and scratching of the bites may lead to secondary infections. Also, the sensation of crawling mites on the skin will irritate some people.

Bird mites do not live underneath the skin and are not associated with any diseases. The mites will bite at random and there are no selected areas of the body that are favoured, but clothed areas of the torso, limbs and the head area are commonly involved. A great deal of discomfort is experienced by the occupants of the building until the infestation is controlled or dies. A bird mite infestation cannot be maintained on humans but will persist while the bird-related source of the mites is maintained.

Laboratory Diagnosis

Identification by high-power light microscopy, using appropriate taxonomic keys, by an expert is the only method of correctly identifying the mite. Although Ornithonyssus bursa is the most common mite associated with infestation of homes there are several other mites associated with birds within Australia that can invade and bite humans. These bird mites include Ornithonyssus sylviarum (Northern fowl mite) and Dermanyssus gallinae (Chicken mite). Also, a closely related species, Ornithonyssus bacoti (Tropical rat mite), is associated with commensal rodents (rats and mice) and their nests located in houses and other buildings; these mites are occasionally linked to attacks on humans, and Ornithonyssus bursa and Ornithonyssus bacoti are taxonomically very similar and are extremely difficult to differentiate. Correct identification is absolutely necessary if appropriate control procedures are to be recommended.

Treatment and Control

The irritation associated with bites can be alleviated with an anti-pruritic such as crotamiton (e.g. EURAX ^R) but there is no specific treatment. Severe reactions may have to be treated as for other allergic conditions with antihistamines.

Once the mite has been correctly identified, appropriate steps must be taken to remove the source of the infestation and prevent its recurrence. All nesting sites should be located, and the nesting material removed and the area cleaned to prevent other birds or inhabitants utilising the nest.

An insecticidal spray can be applied to ensure total eradication of mites, but fumigation of rooms without removal of nests in roof cavities will not stop further mites entering and the problem will continue. Broken tiles or timber allowing access to roof cavities should be repaired, and all potential entry points to the eaves and roof cavity blocked. Roosting and nesting sites on window ledges should be cleared and made unsuitable for future bird use, if possible. A pest control officer may have to be employed to undertake these control measures, especially if large areas are involved.