Human Lice

Material used in this chapter was adapted from extension publications from the following states:

Human lice infestations can be detected by the feel of something crawling over the skin or by using a hand lens or reading glass to see the minute grayish louse. Infestations can cause intense itching and scratching and, in severe situations, result in scarred, hardened, pigmented skin known as "hobos disease." Inspection of the hair may reveal louse eggs (nits). Outbreaks seem to be associated with crowded conditions with limited facilities for bathing and laundering.

Human lice are small, wingless insects with sucking mouthparts, head narrower than the thorax and legs designed for grasping hairs or fibers. The body louse (about 1/8 inch long) is similar to the head louse (about 1/6 inch long). Both have grayish-white bodies; the head louse has dark areas along the abdominal side. The crab louse is broadly oval, somewhat crab-shaped with large claws on the middle and hind legs, about 1/16 inch long and dirty white to pink. Lice eggs are 1/16 inch long.

LIFE CYCLE

The three species of lice are similar in development. Egg are cemeted to hairs, by the head or crab louse, and to clothing fibers and seams by the body louse. Eggs hatch in eight to 10 days at 80 F to 85 F. Eggs do not hatch when temperatures are below 70 F for seven to nine days. The louse nymphs (immatures) feed on blood meals and molt three times before becoming sexually mature adults. Mated females deposit eggs daily over a 20- to 30-day period. Body lice deposit 275 to 300 eggs, head lice 50 to 100 eggs and crab lice about 30 eggs per female. The entire life cycle requires 18 to 27 days, with the adults living up to 35 to 40 days.

Body Louse Pediculus humanus humanus L.

Female lice lay 6-7 eggs per day and may lay a total of 50-300 eggs during their lives. Under normal conditions the eggs will hatch in 5-10 days, averaging seven days. The young lice that escape from the egg must feed within 24 hours or they will die. The nymphs and adults all have piercing-sucking mouthparts, which pierce the skin for a blood meal. Adults may survive 3-5 days without a blood meal. The adult body louse can survive no longer than 10 days off its host. All stages, including eggs, die within 30 days away from the host. Normally a young louse will mature to an adult in 3-5 weeks.

The body louse lives on clothing in close contact with the skin. This louse is most common in overcrowded, unsanitary conditions often when clothing is not changed regularly. People sleeping or huddled together in their clothing aid the spread of lice. Lice infested clothing in lockers, closets or bedding are sources of infestation. This louse is a vector of several diseases, such as epidemic typhus and relapsing fever.

Head Louse Pediculus humanus capitis DeG.

Female head lice produce from 50 to 150 eggs which they usually attach to hair behind the ears, on the nape and occasionally to other body hairs. Nits (egg) are attached to the hair shaft at the scalp with a waterproof cement-like substance. Although lice and nits are most commonly found at the nape of the neck and behind the ears, they can be found anywhere on the scalp. The greyish white nits (1 mm. long) are shaped like an elongated football with a cap at one end to admit air and allow the young insect to escape. The eggs hatch in 5 to 10 days, and the young, which resemble the adults except for size, mature in 8 to 10 days during which they undergo three skin molts to allow for body growth. Adults normally live about 3 weeks or more, depending upon conditions.

The head louse commonly infests school children, in addition to adults. These lice are spread by direct contact with infested persons, or by using infested articles, such as hats, wigs, hairbrushes, combs, towels, scarves and hair rollers. Nits may also be found in headgear, a common means of spreading. The incidence of infestation is greater among persons with long or dense hair, particularly when regular and thorough grooming is neglected. Lice may also be spread among the population by using the bed or other furniture of an infested person. Head lice are usually not found below the neck of an individual, but were recorded in armpits and even the chest.

Crab or Pubic Louse Pthirus pubis (L.)

Crab lice live on the hairy portions of the body. Their legs are adapted to grasp hairs which are rather widely spaced, and for this reason, these lice prefer the pubic and perianal regions.

Female lice produce about 25 eggs and glue them to coarse hairs. The eggs hatch in one week into nymphs which mature to adults in 15-20 days. Adult lice suck blood periodically, injecting a saliva into the wound which causes pale blue spots from 0.125-1.0 inch in diameter.

Crab lice are found primarily in the pubic region, but may occur in the armpits, beards and eyebrows. These lice may be spread during sexual intercourse and only rarely are spread by loose hairs left on bedding and toilets by infested persons. Crab lice die after 24 hours if not attached to a human.

FREQUENTLY ASKED QUESTIONS ABOUT LICE

LICE CONTROL

Control of human lice is a medical problem that must be left to a physician, pharmacist or health department personnel. Chemical treatment of these premises is seldom necessary because lice cannot live off the host for indefinite periods of tune. Schools, jails, hospitals, boarding houses and other crowded living quarters need a public educational program for effective lice control.

The position of nits on the hair shaft can distinguish between current and past infestation because female lice attach their eggs to the hair shaft at the scalp. In 1 week, the time it takes for a louse egg to hatch, human hair grows about 1/4 inch, carrying the egg with it. Therefore, nits more than 1/4 inch from the scalp either have already hatched or will never hatch. They may remain attached to the hair shaft for months, but play no role in the transmission of head lice. Removing these dead or empty nits with a fine tooth comb is for grooming purposes only.

Elimination and Prevention

Proper sanitation is critical in lice control. Hair should be washed frequently, bedding and undergarments laundered, clean clothing worn and premises thoroughly cleaned with hot water and a strong cleaning agent, such as disinfectant. Laundering or dry cleaning infested bedding and garments will kill body lice. Adult lice are killed within five minutes and the eggs within 10 minutes in 125 F water. Regular changes to properly laundered clothing will soon eliminate body lice. Long hair tightly braided and thoroughly combed each day ean minimize head lice problems. Special combs with teeth set close together are used to remove nits and adult head and crab lice. These combs, available at pharmacies and pet shops, can also be ordered from Cereal Soaps, Division Johanson Manufacturing Corp., Box 329 Boonton, NJ 07005.

Insecticides

Chemicals are available as prescription or nonprescription drugs to manage lice. These drugs are available as creams, lotions, or shampoos. Shampoos are preferred for management of head lice. The application of these insecticidal drugs will kill nymphs, adults and some eggs. Because some eggs may survive, it may be necessary to treat once per week for three weeks to insure complete management. Even though the nits may be killed, the unsightly eggs may remain glued to the hair. These eggs may be removed by combing with a fine-toothed comb or nit picking.

Prescription and nonprescription medications are highly effective in killing lice, but some eggs may survive. Retreatment in 7 to 10 days is necessary to kill any newly hatched lice. This second treatment is very effective in killing the newly hatched lice before they have a chance to lay eggs and continue the infestation. Failure to do a second treatment in 7 to 10 days may lead to the continuation of the lice infestation. The newly hatched lice do not play a role in transmission. School children with head lice may return to class as soon as they have received their first treatment with an effective medication.

Nits found on hair within 1/4 inch of the scalp in a person who has not been treated should be considered evidence of an active infestation which requires treatment. Children found to have nits within 1/4 inch of the scalp should be treated for their infestation and may return to school immediately after the first treatment. They should still receive a second treatment 7 to 10 days later. Nits found on hair over 1/4 inch away from the scalp either have hatched or are dead. They play no role in the transmission of head lice to others. Therefore, children with nits over 1/4 inch away from the scalp should not be excluded from school.

A home or school should not be sprayed, dusted or otherwise treated with insecticides when an inhabitant has lice. Lice do not hide in wall crevices and floor cracks like cockroaches and other household pests. Treatment of homes, schools, or other dwellings with insecticides would, therefore, be wasted and possibly harmful. Cleaning carpets, upholstered furniture, etc. should be limited to simple vacuuming.

Soap and water will kill lice in bedding if the water is hot enough ( 130 degrees F). All clothing and bedding used during the 2-day period prior to treatment should be laundered. Such high temperatures are suitable for laundering purposes but not for shampooing the head or for bathing. Dry heat, steam, or pressing with a hot iron will destroy lice because they can live only a few minutes at 130 degrees F. Most home water heaters supply water at sufficient temperatures to kill lice and their nits. Washing in cold or lukewarm water will not kill lice, so sufficient time between loads of laundry should be allowed for the water to reheat. For those items of clothing which cannot be washed, dry cleaning will also kill lice and their nits. An alternative method is to seal clothing in a plastic bag for 2 weeks. This will kill all lice and their nits.

Combs, brushes and similar items can be treated by soaking for 1 hour in one of the special medicated shampoos or by soaking them for 5 to 10 minutes in a pan of water heated on the stove to 130 degrees F.

To avoid becoming infested with head lice, family members should be inspected and undergo treatment if necessary and be taught not to share other people's combs, brushes, scarves, etc. At school, children's clothing and other personal articles should be kept separate from those of other students (for example, on pegs, in separate storage areas or on the backs of chairs). A school screening program can help keep head lice from becoming an epidemic.

CONTRIBUTING AUTHORS

Human Lice. Harry Williams and Jaimes Yanes, Jr. University of Tennessee Agricultural Extension Service Publication SP341S.

Human Lice. University of Florida, Institute of Food and Agricultural Sciences.

Management of Head Lice. Mike Potter, University of Kentucky, Department of Entomology.

Human Lice. Philip J. Hamman and J.K. Olson, Texas Agricultural Extension Service Publication L-1315.

Controlling Head Lice. Gene R. Strother, Alabama Cooperative Extension Service, Auburn University, Circular ANR-798