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Lice

When we hear the word "lousy," we rarely think of its original meaning, which is "infested with lice." In times past, indeed, lice infestation was rampant, and it still is rampant now in conditions of poverty or wartime. Lice, particularly head lice, are also common among schoolchildren of all socioeconomic groups.

Definition

Lice are wingless insects, in contrast to ticks or mites, which are arachnids related to spiders and scorpions. Human lice are uniquely adapted to living on human beings. Other animals have their own lice.

Transmission

Lice may be transmitted by direct human contact or by contact with infested clothes, bed sheets or other "fomites." (A fomite is an inanimate object, such as a brush, comb, hat, tool or garment which may carry infection.)

Types of Lice

Head lice

The head louse (Pediculus humanus var. Capitis) is probably the most common type we see at present, particularly among schoolchildren. How many of us have received notices from our children’s school that cases of head lice have been found at the school! Children touch each other far more than adults, and such conditions favor the spread of lice. Diagnosis is made either by finding the lice (which may be tricky, as they are quite adept at hiding) or, more commonly, by finding the ova (eggs) of the lice, known as "nits." A skilled examiner may be able to determine on microscopic examination whether the ova are viable (live) or whether they are empty shells.

This may be important in assessing the success of treatment.

Pubic lice

The pubic louse (Phthirus pubis) is generally spread by direct contact, often sexual contact, but may often be spread by contact with infested clothing or bed sheets. Shared sleeping bags are a common source. Perhaps surprisingly, infested people often do not realize that they have lice. They may itch, and they are usually aware that something is going on, but the lice are small and may easily be taken for smalls scabs. When one is removed and examined under the microscope, it is easy to see how they have acquired the nickname "crabs". The legs have a large claw-like appearance. The lice cling to hairs with these "claws," usually in the suprapubic area. However, it is quite common for pubic lice to be present in other hair-bearing areas of the body, including the chest, back, armpits and even eyelashes. (I have yet to see pubic lice in the scalp.) Diagnosis is made by finding the lice.

Body lice

Body lice (Pediculus humanus) are most common among conditions of squalor, including wartime conditions among troops and the civilian population, and among derelicts, such as the homeless. These lice are often most readily found in the folds of clothing, but may be found on the body. They look similar to head lice.

Prevention of transmission

Naturally, an infested individual should avoid direct contact with others until treated. The affected individual's personal items, such as combs and brushes, should not be used by others, and they should be carefully cleansed or replaced. Clothes, including hats, and bed linens should be cleansed with a hot wash or placed in dry storage for a week or two. Sleeping bags have been a frequent mode of transmission in the past and should also be cleansed or placed in dry storage. Intimate contact should be avoided until after treatment. If there has already been close or intimate contact, consideration should be given to treating those who have been in contact, even if there is not obvious evidence of infestation.

Treatment

A number of alternate treatments are currently available, mostly topical creams or lotions. I personally favor a prescription lotion called Ovide®, which contains malathion (0.5%). This medication is left on for approximately 8 to 12 hours, although recent studies indicate that such a lengthy application may not be necessary. A second treatment may be required in one week to completely eliminate the lice. As already mentioned, "fomites" such as brushes, combs, hats, clothes and bed linens should be thoroughly cleansed. Other treatments include preparations containing lindane (now banned in California), permethrin (available in 1% or 5% strengths) or pyrethrin (available over the counter). Yellow oxide of mercury in petrolatum has been used for lice of the eyelashes. Plain petrolatum, used correctly, can also be effective. Some of these treatments may be toxic or downright dangerous if not used correctly, and the appropriate treatment should be determined after consultation with your doctor.

After treatment of head lice, it is essential that all the nits (eggs) are thoroughly removed from the hair with a fine tooth comb. The nits are firmly cemented to the hairs, so such removal may be laborious, but it is the most effective (and usually the only) way of knowing whether the treatment has worked.

Resistance

We have, unfortunately, been witnessing the emergence of strains of lice resistant to traditional treatments, particularly permethrin and pyrethrin. However, before concluding that a treatment has not worked, ensure that it has been done correctly and also that reinfestation has not occurred. That said, there are indeed now strains of truly resistant lice. A simple approach to treating lice is to use petrolatum. Both the lice and the nits need oxygen to breathe and this is simply a way of smothering them. If done correctly it is enormously messy, but it works! Another option for resistant lice is the use of the oral medication, ivermectin. This is a systemic drug approved for certain parasitic infestations, but not yet for lice. It should be used only under the careful supervision of a physician.