Symptoms of Head Lice and Treatment

Human lice are wingless bloodsucking insects that have been feeding on humans for thousands of years.

Head, crab, and body lice are still a problem in modern times, with hundreds of millions of cases of pediculosis reported each year.

Head lice are the most common of the three pediculosis types and are a constant annoyance. They can be found in people of any age, gender, race, or socioeconomic status.

Schoolchildren aged 3 to 11, particularly girls with long hair and a proclivity to share hair care tools and accessories, are most vulnerable.

Head Lice Infestation

African-American children are less likely to be affected, possibly as a result of the shape or texture of their hair creating an environment that is less conducive to lice survival and reproduction.

Crab (pubic) lice are primarily transmitted through sexual contact, with men aged 15 to 40 having the highest incidence.

Body lice tarnish the reputation of all lice. They not only contribute to poor hygiene, but they also serve as disease vectors for epidemic typhus, relapsing fever, trench fever, and bacillary angiomatosis or endocarditis.

The three different types of lice are all obligate human parasites that only feed on human blood and can't last very long without their human host. They differ in size, shape, and preferred body area location.

1. Head Louse

As the name implies, the head louse, Pediculosis capitis, prefers scalp hair. It is light tan to medium brown in color and roughly the size of a sesame seed. Although it cannot jump or fly, it moves very quickly and can be difficult to see. The female louse lives for approximately 30 days and lays 5 to 10 eggs per day. For warmth, oval egg capsules or nits are cemented to hair shafts near the scalp.
Direct contact or fomites such as combs, brushes, hats, helmets, and headphones are used to transmit lice; however, static electricity and blow dryers have been shown to launch lice into the air, creating another possible mode of transmission. Keep reading to know the difference between a head louse and body louse.

The body louse, Pediculosis corporis, is slightly larger than the head louse, measuring 2 to 4 mm in length, but otherwise looks similar.
It is distinct from head lice and crab lice in that, while it feeds on humans, it does not live on them; instead, it lives in clothing and lays its eggs along the seams.

Crab lice, Phthirus pubis, are smaller and wider than head lice and have the appearance of tiny crabs. Although crab lice are commonly referred to as pubic lice, this is a misnomer because crab lice have evolved to ambulate across the entire body surface.
In addition to pubic hair, the infestation can affect the scalp, brows, eyelashes, mustache, beard, axillae, and perianal area.

A patient with lice will typically present with intense itching in the area of infestation and a history consistent with exposure.

Nonspecific clinical findings include erythema, papules, wheals, excoriations, hemorrhagic crusts, and, on rare occasions, scale. Head lice most commonly infest the occipital scalp, posterior ears, and neck; crab lice infest the lower abdomen, pubic area, and thighs; and body lice infest the back, neck, shoulders, and waist. Pyoderma and regional lymphadenopathy are possible.
Macula cerulea, or small blue dots, can be found at the site of lice and flea bites. In cases of body lice, nits may be seen on proximal hair shafts or on clothing seams. Identifying a live louse is the only way to make a definitive diagnosis of active infection, but because lice avoid light and move quickly, this is difficult. It has been demonstrated that wet-combing detangled and lubricated hair with a specially designed nitcomb is a sensitive method of harvesting and identifying live lice.

The presence of lice or nits on hair, skin, or clothing seams is a key diagnostic feature of pediculosis.

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Body lice are typically treated successfully by bathing the patient and bagging and disposing of infested clothing and bed linen. If clothing cannot be discarded, it can be washed for 30 minutes in hot water (at least 149°F), dry cleaned, or hot ironed (especially in seams).
If nits are found on body hair, a single 8- to 10-hour application of 5% permethrin cream to the entire body, similar to scabies treatment, is the best treatment option.

Topically, crab lice can be treated with 1% and 5% permethrin cream or 1% lindane shampoo. The most effective and safest topical treatment is 5% permethrin cream applied overnight to all hair-bearing areas, washed off in the morning, and repeated 1 week later.
Topical pediculicides cannot be applied to the eyelashes, making treatment difficult. If at all possible, nits and lice can be physically removed with fingernails or a nitcomb, or ophthalmic-grade petrolatum ointment (only available with a prescription) can be applied to the eyelid margins 2 to 4 times per day for 10 days.
Regular petrolatum jelly (Vaseline) should not be used in this area because it can cause eye irritation.
Although not FDA-approved for crab lice, oral ivermectin has been recommended for patients with perianal or eyelid involvement or when topical treatment fails. The recommended dose is 200 mcg/kg, followed by a week off. Individuals with crab lice should be tested for sexually transmitted diseases, which frequently occur concurrently.