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University
of Rhode Island GreenShare Factsheets
Lice
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.
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 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.
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.
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.
- 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.
- Shampoo again, leaving the lather on for 15 minutes with
a towel around the head. Read or provide interesting activity.
- 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.
- When all the hair has been combed, rinse well with tolerably
hot water. Heat will kill lice.
- Dry hair. Check for stray nits or the gray to yellow
eggs. Remove with tweezers or comb.
- 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.
- Repeat weekly, more often if necessary, for three to
four weeks. Check often.
- 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:
- 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.
- Never resort to dangerous remedies such as lindane, kerosene
or pet shampoos.
- 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.
- 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.
- 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
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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