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Facts about pubic lice

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Illustrasjon: FHI

Pubic lice (Pthirus pubis) are one of three types of lice that can live on humans. The other two are head lice and body lice. Pubic lice occur in Norway, but are rare. They live mainly in the coarse body hair around the genitals and under the armpits, and are transmitted by sexual intercourse or other close bodily contact. Lice suck blood and their bites itch.

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What do pubic lice look like?

Pubic lice have a broad, almost square, body and are about 2 mm long in adulthood (Figure 1). They are grey-white in colour. The abdomen is wider than long, with small growths on the sides. The front leg is thin with sharp claws. The two rear leg pairs are thick with powerful claws to cling to the hair. The eggs are 0.7 mm long and yellowish.

How do pubic lice live and develop?

Pubic lice mainly live in the hair around the genitals and anus, as well as adjacent areas such as the stomach and thighs. Armpits are also a common site. However, they can appear in any body hair, including beards, moustaches, eyebrows and eyelashes.

Pubic lice are more site-specific than body lice and head lice. They spend most of their time at the base of the hairs. With a solid grasp of two hairs and their mouth parts in the skin, they suck blood periodically. They move nearly every day, but usually only a few millimetres (very rarely 10-15 cm).

The female lays many eggs on a single human hair. The eggs are stuck very firmly with a secretion. They hatch after 7-8 days.Over the next 13 to 17 days the larvae will change skin three times before reaching adulthood. Adult lice live for just under a month. Pubic lice can only survive and reproduce on people.

How are pubic lice transmitted?

The infection usually occurs by close body contact, such as during sexual intercourse or when children share a bed with parents. The infection can also occur via towels, bedding, clothing, etc. This is less common but can occur where many people live together in cramped conditions such as sailors and soldiers. Pubic lice live for less than a day when removed from the body.

How are pubic lice identified?

Pubic lice are visible to the naked eye, and can be detected by careful inspection.

Blood sucking will eventually lead to itching caused by an allergic reaction to the bites. For the individual, the louse population is usually small, and it may take time before the itch gets so annoying that lice are discovered. There is a big difference in reaction to bites from person to person. For some, the itch is less than from head and body lice, while others have severe itching and eczema. Pubic lice bites typically cause irregular, blue spots in the skin around the bite. The spots develop a few hours after the bite and last for several days. Not all bites cause this reaction.

Statistically, there is an association between the occurrence of pubic lice and other venereal diseases like gonorrhea or syphilis.

If pubic lice are observed, the sexual partner should be informed, so they can check for infection and seek treatment. Children should also be checked if their parents are infected.

How are pubic lice treated?

Pubic lice must be treated with a lice treatment. Lotions or shampoos with malathion or a cream with permethrin are recommended medicines. Information is available from pharmacies. Treat all areas of the body with hair, except eyelashes and eyebrows. Check these for lice and eggs and remove any hair with eggs with tweezers.