HUMAN LICE

Human lice historically have been associated with social upheavals, substandard and crowded living conditions, poverty, wars and lack of personal hygiene. Ironically, during the current period of the highest living standards in history, the incidence of louse infestations, particularly head lice, appears to be increasing in the United States. Some authorities have attributed this increase to currently popular longer hair styles, communal living and uncleanliness. Head lice spread easily, however, and infestations often occur at all social and economic levels, especially among school children who are in close, daily contact.

In addition to the head louse (Pediculus humanus capital), the body louse (Pediculus humanus humanus) and the crab louse (Pthirus pubis) occur on humans. All three are bloodsuckers and cause considerable skin irritation and itching when they feed or crawl on the body. Although not currently a problem in Texas or the United States, typhus and relapsing fever are readily transmitted by body lice. Human lice, which can establish and maintain themselves only on humans, are rarely contracted from or passed on to pets or other animals. A louse cannot hop or jump. They are usually transmitted through close personal contact. They are less frequently transmitted through the sharing of personal articles. For head lice, this includes combs, brushes and other grooming aids; hats, headbands, caps, wigs, curlers, or other headgear; or storing these items in shared lockers.

Figure 1. Body louse and head louse.

Head lice and body lice, which are different forms (subspecies) of Pediculus humanus, are similar in appearance. Their habits are distinctly different, however. About 2 or 3 mm. long when mature, lice are wingless insects whose legs have claws that are adapted for clinging, giving the insect a strong grip on hair shafts. Their abdomens are distinctly longer than wide. Their color, which varies from dirty-white to grayish-black, usually approaches the hair color of the host. Head lice almost always occur on the head where they attach their eggs (nits) to the hair; body lice prefer to live in the seams and linings of clothing, blankets and sheets from which they periodically crawl onto the skin to feed. Although body lice usually deposit their nits on clothing fibers, they are sometimes found on body hair as well.

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.

Figure 2. Crab louse.

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 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. 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.

Body lice females may deposit 200 or more eggs, usually attaching them to clothing fibers. The development period is similar to that of head lice. The life history of crab lice is also similar except that the young require 2 to 2 1/2 weeks to mature and the adults normally live about a month.

Human lice cannot survive for long when separated from their host. Head and body lice leave the host or clothing voluntarily only when the host has died or become hot with fever, or when they try to avoid strong light or to transfer to another host in close contact. Human lice are completely dependent upon human blood for sustenance. Lice feed frequently, usually every 3 to 6 hours, and do not usually survive more than 48 hours away from the human body.

Crab lice usually die within 24 hours after separating from the host. This short survival and their sluggish movement inhibit the spread of crab lice, except through intimate personal contact or in crowded living and sleeping conditions under which they can spread readily. Crab lice may be (but rarely are) spread by nits on loose hairs left on bedding and toilets by infested persons.

Head lice attach each nit (egg) 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 (1mm. long) are shaped like an elongated football with a cap at one end to admit air and allow the young insect to escape.

Figure 3. a. Head louse nit attached to hair. b. Body louse nit attached to clothing f ibers. c. Crab louse nit attached to hair.

The presence of nits does not always mean that a person has a current infestation. The nits may be left from a past infestation that has been adequately treated. To determine whether a person is currently infested with head lice, there must be a louse present or there must be nits on the hair shaft 1/4 inch or less from the scalp.

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.

Itching is the most common symptom, but most persons with very light infestations experience no symptoms at all. Therefore, you cannot rely on itching as the only way to detect head lice. A thorough examination of the hair and scalp is necessary to detect head lice or nits. Persons infested with pubic lice should be examined for accompanying venereal diseases, because there is a strong possibility that one is present with the other. Persons who think they are infested with lice should seek assistance from a physician, the health department or the school nurse and follow their instructions. These instructions will usually include a schedule of a specially medicated shampoo; the laundering of bedding, clothing and towels in hot water; and the washing of combs and brushes. The entire family and school contacts should be inspected and undergo simultaneous treatment if necessary.

CONTROL

Safe and effective over-the-counter medications (shampoos and lotions) are available at most pharmacies. The most widely accepted are those based on natural compounds called pyrethrins, A-200 Pyrinate) and RID, which are fast, effective killers of pests such as lice. Others containing differ ent medications include Cuprex and Bornate. Prescription treatments include Topocide, Kwell Shampoo, Kwell Lotion and Kwell Cream. The Kwell products contian lindane (gamma benzene hexachloride).

R&C Spray and LI-BAN Spray, containing phenothrin, may be used to help prevent reinfestation and transmission of lice to other household members. These products should be used only on garments, bedding, furniture and other inanimate objects that cannot be either laundered or drycleaned.

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.

For more information on pest control and pesticide products, see Extension publication B- 1373 House and Landscape Pests.

Insecticide label clearances are subject to change and changes may have occurred since this publication was printed. The USER is always responsible for the effects of pesticide residues on plants or household goods, as well as problems that could arise from contamination of neighboring property and plants.Always read and follow carefully the instructions on the container label.