Three kinds of lice can infest humans - head lice (Pediculus capitis), body lice (P. humanus) and crab (or pubic) lice (Phthirus pubis). Human lice infestations, also known as "Pediculosis," affect persons of all ages, whether rich or poor, from the Arctic to the Tropics and throughout history. Blood is the only source of nourishment for lice.

Infestations can cause persistent itching and scratching on the scalp. Usually in severe situations, scarred, hardened, pigmented skin known as "Vagabond's Disease" may occur along with a rash and swollen lymph glands in the neck or under the arms.

Inspection of the hair by a hand lens or magnifying glass may reveal small, silvery louse egg cases (nits) attached to individual hairs and/or minute, grayish specks moving within the hair, usually at the back of the head and behind the ears.

Pediculosis is spread mainly by direct contact with an infested person or stray hairs containing nits, personal items such as wigs, combs, hairbrushes, hair rollers, towels, pillowcases and clothing, especially hats, sweaters, scarves, etc. Treatment should be made immediately since lice populations can spread rapidly and throughout the family, school and other close living quarters. Most lice that fall off the hair will not usually survive longer than two to three days, while nits can remain viable for up to 14 days off the human host. Human lice are not transmitted by pets such as dogs, cats, gerbils, birds, etc--these lice do not survive on domestic animals.

Identification

Human lice are small, wingless insects, flattened in shape from top to bottom with sucking mouthparts. The head is narrower than the thorax, and the legs are 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 (nits) are about 1/30-inch long or about the size of a period at the end of a typed sentence.

Life Cycle and Habits

The three human lice species are similar in development. The head or crab louse cements its eggs to human hair and the body louse cements its eggs to clothing fibers and seams. Eggs hatch in five to nine days. The louse nymphs (immatures) feed on the blood and molt three times before becoming sexually mature adults. Mated females begin depositing eggs daily for 20 to 30 days. 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 about 21 to 27 days, with the adults living up to 35 to 40 days. Both nymphs and adults feed on blood several times a day, injecting irritating saliva into the wound that causes intense itching. Scratching increases inflammation of the bites, sometimes leading to secondary bacterial infection. Lice cannot jump, hop or fly and have limited ability to crawl when away from the host.

The body louse commonly infests people living in overcrowded, unsanitary conditions where clothing is not changed regularly. People sleeping or huddling together in their clothing cause these lice to spread rapidly. Lice-infested clothing with eggs in lockers, closets or bedding are sources of infestation. This louse is a vector of human diseases such as epidemic typhus and relapsing fever. The adult body louse can survive no longer than eight to ten days off the host, and all stages, including eggs, die within 30 days away from the host.

The head louse commonly infests school children since there is close contact with each other at school and at play. Eggs are pearly white (half the diameter of a pinhead) and will not brush off like dandruff. Nits are firmly attached to the hair shaft close to the scalp behind the ears and on the back of the neck. Adult lice are spread mainly by direct contact with infested persons or by using infested articles such as hats, wigs, hairbrushes, combs, towels, scarves and hair rollers. Even using the same bed or sitting on upholstered furniture that an infested person used can spread lice. Head lice are usually not found below the neck of an individual but have been recorded in armpits and even the chest. Usually children under 12 years of age are more sensitive to lice feeding than any other age group. Head lice can survive off the host two to three days.

Crab lice are found primarily in the pubic region but can occur in the armpits, beards and eyebrows. These lice are spread during sexual intercourse and only rarely are spread by loose hairs left on bedding and toilets by infested persons. Crab lice die after 12 to 48 hours if not attached to a human.

Control Measures

Control of human lice is a medical problem that must be left to a physician, pharmacist or health department personnel. Treating the premises is seldom necessary since lice cannot live off the host for indefinite periods of time. However, when a premise treatment is required or demanded, permethrin 0.50 percent spray is labelled for bedding and furniture (not for use on humans or animals) for body lice (not necessary for head or crab lice). Some apply spray to body louse-infested clothing in lockers and closets. However, many feel that premise sprays are unnecessary. Schools, jails, hospitals, boarding houses and other crowded living quarters need a public health educational program for effective lice control.

Back-to-school is an excellent time to educate teachers, parents, children and the community about lice. Before an outbreak occurs, persons should understand the communicability of lice, how to make accurate diagnosis and how to treat children in the safest and most effective methods. (September is National Head Lice Prevention Month.) Education programs should include school systems, child care centers, drugstore chains, pharmacies, health departments, camps, hair salons, school nurses, parents, physicians, etc.

Prevention

Proper sanitation is critical in lice control. All members of the family must be checked for lice (only those who are infested should be treated). Hair should be washed frequently, bedding and undergarments machine laundered, clean clothing worn and the premises thoroughly vacuumed. Laundering (using hot water) or dry cleaning infested bedding and garments will kill all kinds of body lice. Adult lice are killed in five minutes and the eggs in ten minutes in 125 deg F water. Regular changes to properly laundered clothing will soon eliminate body lice. Hairbrushes, combs and barrettes can be soaked in hot water (140 deg F) for 20 minutes provided these items are not damaged by heat. Long hair, tightly braided and thoroughly combed each day can minimize head lice problems. Special combs with teeth set close together are used to remove nits and adult head and crab lice after insecticide treatment. Often these combs are available at pharmacies and pet shops. Thoroughly vacuum carpets, rugs, pillows, mattresses, etc. to remove fallen hairs with attached nits. Avoid close contact in unsanitary, crowded conditions when possible.

Chemical Control

Once lice have been identified, prompt treatment is the key to effective control. Medicated shampoos, lotions and gels are available both over-the-counter (nonprescription) and from physicians (prescription). Several nonprescription products contain pyrethrins (Rid, A-200, Pronto Conc., Inno Gel Plus, Pediculicide Liquid II, R & C shampoo, R & C Lice Treatment Kit, and permethrin (Nix). A lice shampoo is applied to the hair for 10 minutes, washed or rinsed out followed by a special lice removal comb to remove dead lice and their eggs. A commercial liquid solution of Clear Lice-Egg Remover is marketed to loosen the attached nits from the hair strands so that removal by comb is much easier. Some lice treatment kits contain a 5X magnifier to easily see the lice and nits to avoid misdiagnosis of dandruff and hair spray drops. Since lice eggs are not always killed, retreatment may be made in seven to ten days to kill any newly emerging lice. Pyrethrins (Rid) will not kill the eggs or nits. Permethrin (Nix) is labelled as a creme rinse to kill both eggs and lice, providing 14 days protection from reinfestation.

The only prescription product is lindane (Kwell) cream, lotion or shampoo. However, it is not recommended since lice control failures have occurred; it is more toxic to humans than the recommended alternatives. Other labelled Pediculicides include ammonium phenate bromide complex (Microban), amorphous silica gel (Drione, Tri-Die), resmethrin (Vectrin)and sumithrin (Steri-Fab).

Unfortunately, head lice are often very difficult to control. There are many, many reports of treatment failures for allcurrent, commercially available Pediculicides both nonprescription and prescription. (There are no known answers, at this time, to the present serious problem of lice resistance to pesticides.)

It is reported that Cas-Tile soap will effectively kill lice. Also, snipping or cutting out individual hair strands containing nits is often very helpful.

Here is a nontoxic head lice control plan described in "Common-Sense Pest Control," an entomology textbook.

1. Shampoo with coconut-oil or olive-oil shampoo, such as Condition 3 in 1, Rave, St. Ives Swiss, or V05. Coconut and olive oils will kill lice. Rinse with water only as hot as the child can tolerate.
2. Shampoo again, leaving the lather on for 15 minutes with a towel around the head. Read or provide interesting activity.
3. Comb to get out snarls and suds. Then, with a nit comb under good lighting, comb one inch-wide sections of hair, starting at the scalp where eggs are laid. Keep hair wet, clipping finished sections aside. Clean the comb often with tissue, placing soiled tissues in a bowl of soapy water to dispose of in the toilet. Nit combs are available at most pharmacies.
4. When all the hair has been combed, rinse well with tolerably hot water. Heat will kill lice.
5. Dry hair. Check for stray nits or the gray to yellow eggs. Remove with tweezers or comb.
6. Soak comb 15 minutes in 2 cups of hot soapy water with one teaspoon of ammonia or boil metal comb for 15 minutes. Clean with floss or old toothbrush.
7. Repeat weekly, more often if necessary, for three to four weeks. Check often.
8. Wash clothes and bedding in hot water or place in a hot dryer for 30 minutes. BY SHAMPOOING AND CHECKING HEADS OFTEN AND BY TEACHING CHILDREN NOT TO SHARE HATS AND COMBS, YOU CAN HELP PREVENT HEAD LICE.

Persons with concerns or questions about head lice management can be referred to the National Pediculosis Association (NPA), a nonprofit health organization, dealing specifically with this problem. To contact NPA or to become a member and receive educational material (books, screening tools, handouts, mailers, and audio visuals) for a small fee, write to the following: P.O. Box 610189, Newton, MA 02161-0189 or telephone 614-449-NITS.

Some suggestions for head lice treatment failure recently reported in an Iowa newsletter from NPA are as follows:

1. Discontinue use at the earliest sign of treatment failure. Switch to a different product. Do not continue using the same product in hope of killing the lice. Remember lice treatment products are pesticides. Repeated use or increasing the dose could pose health risks.
2. Never resort to dangerous remedies such as lindane, kerosene or pet shampoos.
3. Never use lice spray or flea and tick sprays. The household sprays marketed for treating bedding, cars, rugs, garments and furniture are unnecessary. Vacuuming is a safe and effective alternative to spraying. Parents need not exhaust their physical and emotional selves by obsessive housecleaning and treatment.
4. Manual removal (physical control) is crucial when lice treatment products have failed. Use safety scissors to snip out individual hairs with attached nits. Nit combing doesn't always remove nits, but it can work to comb out lice. Head lice move quickly throughout the head and it is helpful to have at least two people checking an infested person at the same time. Methods to help remove lice include tweezers, fingernails and double-sided tape. Manual removal is tedious and is not considered to be the total solution. It is, however, the only alternative available at this time and serves as a stopgap measure.
5. Continue to check your children for lice often. Early detection and screening for lice and nits are the best ways to manage an infestation.

Adapted from William F. Lyon, Ohio State University Extension, 2001