11.19 Pediculosis (Lice, crabs)
Patients arrive with emotions ranging from annoyance to
sheer disgust at the discovery of an infestation with lice
or crabs and request acute medical care. There may be
extreme pruritis and the patient may bring in a sample of
the creature to show you. The adult forms of head lice
(pediculosis) can be very difficult to find but their oval,
light gray eggs (nits) can be readily found firmly attached
to the hairs above the ears and toward the occiput.
Secondary impetigo and furunculosis can occur. The adult
forms of pubic lice (pthirus or crab lice) are more easily
found, but their light yellow gray color still makes them
difficult to see. Small black dots present in infested areas
represent either ingested blood in adult lice or their
What to do:
- Instruct the patient and other close contacts on the use of
pyrethrins with piperonyl butoxide (RID), an over-the-
counter louse remedy which should be applied undiluted to
the hair until the affected area is entirely wet. After 10
minutes the infested area should be shampooed and
thoroughly rinsed with warm water. This treatment may be
repeated if necessary, but it should not be used more than
twice within a 24 hr period and it is advisable to wait a
week before repeating treatment should reinfestation occur.
- Alternatively, try one application of permethrin 1% cream rinse.
- Families should also be instructed to disinfect sheets and
clothing by machine washing in hot water, machine drying on
the hot cycle for 20 minutes, ironing, dry cleaning, or
storage in plastic bags for two weeks. Combs and brushes
should be soaked in 2% Lysol or heated in water to about
65 degrees C for 10 minutes.
- Application of a 1:1 solution of white vinegar and water
may help to loosen nits prior to removal with a fine-
What not to do:
- Do not have the family use commercial sprays (R&C Spray or
Li-Ban Spray) to control lice on inanimate objects. Their
use is no more effective than vacuuming.
- Do not let patients use lindane (Kwell) shampoo on mucous
membranes, around the eyes, on acutely inflamed areas, and
do not prescribe it for pregnant women and infants. It is
absorbed and can be toxic to the central nervous system.
Head and pubic lice are obligatory bloodsucking
ectoparasites whose eggs are firmly attached to the hair
shafts near the skin, and incubate for about a week before
hatching. Nits located more than one-half inch from the
scalp are no longer viable.
A common alternate treatment for lice is lindane
shampoo which is only available by prescription. One ounce
is worked into the affected area for four minutes and then
thoroughly rinsed out. Because of the very toxic nature of
lindane, its use should be reserved for those cases that
fail to respond to pyrethrins (RID). Treatment with either
substance may not be ovicidal and therefore re-treatment
after 7 to 10 days is often recommended.
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