Lice

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  Head lice - on WebMD
  Head lice - on MedicineNet

Lice Overview

Lice infestation on the human body (also known as pediculosis) is very common. Cases number in the hundreds of millions worldwide. While lice can occasionally cause significant illness (typhus, relapsing fever and trench fever), a lice infestation is generally more of an itchy and embarrassing experience. Three distinct presentations of lice infection exist -- each is caused by a unique parasite. Head lice (Pediculus humanus capitis) is by far and away the most common infestation and favors no particular socioeconomic group. A genetically close "cousin," Pediculus humanus corporis, is responsible for body lice that is more commonly associated with poverty, overcrowding, and poor hygiene. Pubic lice ("crabs") is caused by Pthirus pubis and is transmitted by intimate and/or sexual contact.

Lice infestation is a uniquely human experience. Lice do not jump or fly from host to host. They cannot be transited via animals but may be transferred by person to person via direct contact and by fomites (inanimate objects -- for example, caps, combs, sheets, etc).

Three different types of lice infest people:

Head lice

The head louse is a grey-white animal about 2-3 mm in length (about the size of a sesame seed). The life span of the female louse is about one month. During this time, she will produce between seven to 10 eggs ("nits") per day and attach them firmly to the hair shaft region close to the scalp or body. These nits, which resemble dandruff, are attached with a gluelike, water-insoluble substance that makes them difficult to remove. After six to 10 days, the nits hatch as nymphs and become adults in 10 days.

Head lice are the most common form of lice infestation. The CDC reports that 6-12 million people in the United States are infested each year. Children aged 3-10 years in preschool, elementary school, and day-care centers are most likely to have lice. All socioeconomic classes are affected. Girls are more commonly infested, but hair length or personal hygiene are not predictive factors. Due to unique hair characteristics, African Americans are less commonly bothered by head lice.

Head-lice transmission is most commonly via direct head-to-head contact. Sharing pillows, caps, headphones, and combs/brushes are notorious ways to transmit head lice. Since the head louse dies due to dehydration within two days if not feeding on their human host, contact with carpeting and couches is less commonly seen as a route of transmission. Most lice infestations are asymptomatic (meaning they cause no symptoms). However, itching of the scalp, neck, and behind the ears are characteristic symptoms. Intense scratching may lead to secondary skin infections (for example, impetigo) and associated enlargement of the lymph nodes of the neck and scalp regions.

The diagnosis is made by demonstration of the louse or nits. Nits are more easily seen when examined using a Wood's light ("black light") that causes them to fluoresce as pale blue objects attached to the hair shafts near the scalp. A fine-tooth comb run through the hair will also demonstrate adult lice and nits.

Body lice

The body louse is slightly larger than the head louse but has the same general appearance. Unlike the head louse, which lives on its human host, the body louse lives in clothing (commonly in the seamed areas) and then transfers to the human host to feed. The life cycle of the head louse and the body louse are similar in character and duration. An important difference, however, is the ability of the body louse to survive for up to 30 days away from its human host.

Body-lice infestation is a prominent public-health problem in communities with large populations dealing with poverty, overcrowding, and poor personal hygiene. Reused mattresses and bed linens as well as communal beds are risk factors.

Itching is the primary symptom of body-lice infestation. Areas where seams of clothing are tightly adherent to the body are the most likely areas of involvement. Waistband lines, and axillary and bra strap regions, are examples of where excoriation (crusts, abrasions, or scabbing) from scratching is commonly noted. Red, itchy bite marks may be seen on the body.

The diagnosis of body lice involvement can be made by identifying lice or nits in clothing, bedding, or linens -- especially in the seam regions.

Bedbugs are related to lice. They hide among sheets, blankets, and in furniture and really do bite during the night when they seek a warm body for a meal. They usually leave brown or black markings on the bed linens and bite in rows, often leaving three or more linear bite marks.

Pubic lice

The pubic louse ("crab louse") is distinct morphologically (somewhat rounded with three pairs of legs on either side of the body from which it takes its descriptive name) from the head and body louse. The female lifespan is slightly shorter (three weeks), and she produces fewer eggs per day (three) than her counterparts. The eggs attach to the base of the pubic hair shaft for approximately six to eight days before hatching.

In adults, pubic lice is transmitted by direct sexual contact; children generally contact the infection via nonsexual transmission from their parents. (Sexual transmission is possible in cases of sexual abuse.) Transmission by bed linens and infested clothing is less likely and doubted by some.

Intense itching of the pubic area is characteristic. Axillary regions, eyelashes, and even the scalp may be involved. Nighttime symptoms are may be more intense. After being bitten, a bluish colored sore may develop in the involved areas. The diagnosis is established by demonstration of crab-shaped lice attached to the hair shaft. Consideration of infection by other sexually transmitted diseases (STDs) should be entertained in any adult with pubic lice. Condoms do not prevent pubic-lice infestation. Contrary to popular thinking, pubic lice are not spread by toilet seats.