Pediculosis - louse, lice diagnosis
Diagnosis is made by observing eggs, nits (empty egg shells), nymphs or mature lice on the patient's head but only people with live lice or live embryos in eggs attached to hair shafts have active pediculosis. Detecting live lice is difficult because nymphs and mature lice can move rapidly through dry hair even though they are unable to jump or hop.
Head lice eggs need body warmth to incubate and therefore attach to hair shafts just above scalp level. Human head hair grows at approximately 0.37 millimetres per day, which makes it possible to estimate the infestation's duration by measuring the distance of the eggs from the scalp. Anything identified several millimetres from the scalp will be a non-viable nit, suggesting chronic infestation. Illumination with a Wood lamp reveals live eggs as fluorescent white and nits as fluorescent grey
It is also important to differentiate between eggs, nits and other debris, such as hair casts — the remains of the hair follicle's inner root sheath — which move freely along the length of the hair, dandruff, dried hairspray or hair gel, hair shaft abnormalities, fungal infections (piedra), folliculitis, scabies, and insect bites.
Using a magnifying glass can assist diagnosis, as can sticking adhesive tape onto an area suspected of being infested and observing whether any lice attach to it, but the most reliable method is to dampen the hair and use a specially-designed head lice detection comb.
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