Pubic lice and scabies

The infection

Two distinct parasites are grouped here because both pass through close bodily contact, including sex. Pubic lice are insects adapted to the coarse hair of the pubis, armpits, beard and occasionally eyelashes. Scabies is caused by a microscopic mite, Sarcoptes scabiei, which tunnels through the superficial layer of the skin where the female lays her eggs. Neither has anything to do with poor hygiene.

Key facts

How it is transmitted

Pubic lice pass through direct prolonged contact, usually sexual, and much more rarely through bedding or towels: the louse survives poorly away from its host. Scabies passes through prolonged skin-to-skin contact: a handshake is not enough, but sharing a bed or having sex certainly is. In heavy infestations, transmission through linen and bedding becomes genuinely possible.

Symptoms

Pubic lice cause itching of the pubic area, sometimes bluish marks on the skin and dark specks in underwear; lice and their eggs are visible to the naked eye or with a magnifier. Scabies causes intense itching, characteristically worse at night, concentrated between the fingers, on the wrists, in the armpits, around the navel and on the genitals and buttocks, sometimes with fine visible burrows. The face is usually spared in adults.

Testing

Diagnosis is clinical in both cases. For pubic lice, seeing lice or eggs attached to the base of hairs is enough. For scabies, the combination of night-time itching, the characteristic distribution and a cluster of cases in the household is strongly suggestive. A skin scraping or dermoscopy can confirm it where there is doubt. Both infestations warrant a full check for other sexually transmitted infections.

Treatment

Pubic lice are treated with a topical insecticide, generally in two applications a week apart to kill lice hatching from eggs; shaving is not necessary. Scabies is treated with permethrin applied once and repeated after a week, or with oral ivermectin in two doses. In both cases, clothing and bedding should be washed at 60 °C or sealed in a bag for several days.

If left untreated

Complications come mainly from scratching: bacterial superinfection, eczema, extensive excoriation. Crusted scabies occurs in immunosuppressed or elderly people: it is extremely contagious and requires reinforced measures. Itching can persist for two to four weeks after successful treatment, which does not mean failure.

Prevention

• Treat all partners and everyone in the household at the same time, even without symptoms.
• Wash linen at 60 °C, or seal it in a plastic bag for at least three days.
• Do not share towels, sheets or clothing during the episode.
• Use the consultation as an opportunity for a full sexual health screen.

After a diagnosis

• Treat the household on the same day: staggered treatment leads straight to reinfestation.
• Continue symptomatic treatment for itching, which often outlasts the cure.
• Go back if itching lasts more than two weeks after the end of treatment or if new lesions appear.
• Inform any institution involved: scabies spreads quickly in shared settings.

A little history

The pubic louse has accompanied humanity for a very long time: genetic studies show it descends from the gorilla louse, which crossed to our ancestors around three million years ago. Scabies, for its part, holds a special place in the history of medicine: in 1687, in Livorno, Giovanni Cosimo Bonomo and Diacinto Cestoni described the mite they had extracted from the burrows in the skin and stated that it was the cause of the disease — the first time a human disease was attributed to a living organism visible under the microscope. Their discovery was forgotten, and it took until 1834 for a Corsican student, Simon-François Renucci, to show at the Saint-Louis hospital in Paris how to extract the parasite with a needle.

Treatments were long sulphur ointments and petroleum; benzyl benzoate appeared in 1937, lindane in 1948 — banned in the European Union in 2008 for its toxicity — permethrin in the 1980s and oral ivermectin in the 1990s, which makes it possible to treat a whole care home or school at once.

Unusually for an STI, pubic lice are in retreat: Australian and British clinics noted from 2006 the near-disappearance of cases, attributed to the spread of full-body hair removal — the parasite has nowhere left to cling to.

How this differs between countries

Two ordinary parasites whose management differs mainly through the availability of ivermectin and who pays.

• Oral ivermectin. Very practical for treating a whole household, it is not licensed for this indication everywhere, which leaves topical treatment as the only option in some countries.
• Reimbursement. Topical treatments are covered in some countries and entirely self-funded in others, which matters when an entire household must be treated.
• Mass drug administration. Where scabies is hyperendemic, notably in the Pacific and parts of Africa, whole-population treatment campaigns have sharply reduced prevalence.
• Institutional outbreaks. Management protocols in care settings vary considerably, although the logic is the same everywhere: treat everyone on the same day.
• Notification. Some countries require reporting of outbreaks in institutions; others do not.

Further reading

• CDC — Sexually Transmitted Infections — detailed clinical and prevention guidance

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