Ectoparasites

Pubic lice | Genital scabies | Crabs | Mites |

Overview

  • The most common genital and pubic ectoparasites infestations are scabies and pubic lice (Pediculosis pubis or crabs).
  • Scabies is associated with crowded living/sleeping conditions and institutional outbreaks have been reported.
  • Pubic lice is found typically in sexually active young people.

Cause

  • Pubic lice is caused by Pthirus pubis
  • Scabies is caused by Sarcoptes scabiei var hominis.

Clinical presentation

Symptoms

Pubic or genital itch (especially at night with scabies) &/or rash

Scabies: genital papulonodule
Crabs: debris in underwear
Complications
Scabies:Complications uncommon and mostly in crusted scabies (institutionalised)
  • Fever (children)
  • Pain on movement
  • Sleep disturbance
  • Secondary infection
Pubic lice: fever, lethargy, irritability (more common in the young and frail)

See STI Atlas for more images.

Scabies:

scabies

Pubic lice:

pubic lice

Special considerations

Scabies:

  • Clinical signs are due to allergy to bites (?blood feeds) by the mite
  • Close, prolonged (15-20min) skin contact, person-person transmission
  • Fomite transmission possible
  • May survive >3 days off host in tropics but <36hrs usually.

Pubic lice:

  • Transmitted by close body contact
  • Survive less than 24 hours off host
  • Fomite transmission plays little role
  • Not a vector for other diseases.

Diagnosis

TestSite/Specimen

Crabs: direct visualisation +/- magnification of crab or nits (egg)

Adult lice infest strong hairs (pubic hair, eyebrows and eyelashes).

Eggs (nits) are strongly attached to the hairs.

Scabies: usually a clinical diagnosis.

Multiple methods requiring moderate degree of skill and equipment. Not usually practical in General Practice.

Characteristic nodule and silvery skin burrows sometimes seen e.g. nodule on glans penis and scrotum concurrently, labial fold nodule, burrows (inter-digital folds, wrists and elbows, around breast nipples in women).

Investigations

Crabs:

  • Usually a clinical diagnosis with or without the aid of a magnifying glass. Mite or egg attached to a hair can be removed from the patient and attached to glass slide with cellotape and viewed under a light microscope.

Scabies: 

  • Not generally available in general practice, seek specialist advice. 

Specimen collection 

Scabies:

  • Skin scrapings taken from burrows with a fine needle to reveal the mite after examination under light microscopy.

Management

Principal Treatment Options
SituationRecommendedAlternative
Scabies

Apply permethrin cream 5% topically to dry skin from the neck down, paying particular attention to hands and genitalia, and under the nails with a nailbrush. Leave on the skin for a minimum of 8 hours (usually overnight) and reapply to hands if they are washed.

The time may be increased to 24 hours if there has been a treatment failure. Repeat treatment in 1 week to improve success rate.

Apply benzyl benzoate 25% emulsion topically to dry skin from the neck down, paying particular attention to hands and genitalia, and under the nails with a nailbrush. Leave on for 24 hours and reapply to hands if they are washed.

Repeat treatment in 7 days.
Pubic lice

Apply permethrin 1% cream rinse to pubic and other hair infested with lice and wash off after 10 minutes.

Repeat treatment in 1 week

 Bioallethrin with piperonyl butoxide.

Crusted scabies (formerly called Norwegian scabies) occurs when the mite population is very high due to poor host immune response, such as people with HIV infection, and also in remote Indigenous communities. Seek specialist advice for treatment.

Treatment advice

Scabies:

  • Avoid close body contact
  • Patient and recent partner/s should complete treatment
  • Apply cream at night, including finger webs and do not wash hands after applying cream
  • Isolate clothes, towels and bed linen from previous 3 days and launder as usual the day after first treatment. Or simply isolate these items for >1 week while mites die
  • Avoid more than 2 applications of treatment to prevent persistent irritation
  • Symptoms/signs may not clear for 2 weeks
  • Anti-pruritic treatments (antihistamine oral medication; calamine lotion and topical steroid creams e.g. hydrocortisone 1% can be helpful).

Pubic lice:

  • Isolate clothes, towels and bed linen from previous 3 days and launder as usual the day after first treatment.
  • Shaving pubic hair and/or removal of eggs is not required.
  • Compared with head ice, resistance to permethrin treatment of pubic lice has not been demonstrated.

Other immediate management

  • Advise no sexual contact for 7 days after treatment is administered
  • Contact tracing
  • Provide patient with factsheet (Scabies, Pubic Lice).

Special treatment situations

Special considerations

Consider seeking specialist advice before treating any complicated or persisting presentation.

SituationRecommended
Complicated or disseminated infection

For less severe crusted scabies, use ivermectin 200mcg/kg PO, on day 1, and second dose between day 8-14.

An additional dose maybe required for moderate–severe scabies, but seek specialist advice.

If secondary bacterial infection (impetigo) is severe, pre-treat with antibiotics to cover S. aureus and/or S. pyogenes before administering anti-scabetic treatment.
Persistent infection

Ivermectin 200mcg/kg PO, on days 1 and 8-14, not before 4 weeks after failure of both topical Permethrin and Benzyl Benzoate.
Pregnant women 
 pregnancy		 Permethrin is safe in pregnancy and during breast feeding.
Allergy to principal treatment choice

Seek specialist advice.
Regional/Remote

No special differences. Scabies may affect entire small remote communities where a whole community treatment regimen may be required. Seek local advice.
Eye lash infestation Permethrin 1% lotion keeping the eyes closed during the 10 min application.
Ophthalmic-grade petrolatum ointment bd 10 days (prescription needed and compounding pharmacist to make).

Contact tracing

Scabies:

  • Simultaneous treatment of sexual contacts/all household members of the past month.

Pubic lice:

  • Simultaneous treatment of recent sexual contacts/all household members.

Follow up

Review in 1 week provides an opportunity to:

  • Confirm patient adherence with treatment and assess for symptom resolution
  • Confirm contact tracing procedures have been undertaken or offer more contact tracing support
  • Provide further sexual health education and prevention counselling.

Test of Cure (TOC)

Not required.

Retesting

Not required but provides an opportunity to consider testing for other STIs, if not undertaken at first presentation, or retesting post the window period.

Special considerations

If itch and rash persist, reassurance and anti-pruritics (as above) may be helpful.

Auditable outcomes

  • 100% of diagnoses of pubic lice and scabies are treated with permethrin 1% and 5% as first line therapy, respectively.
  • 100% of patients diagnosed with pubic lice and scabies have STI and HIV testing.
Last Updated: Wednesday, 11 July 2018

Useful links and resources

Taking a sexual history & contact tracing

Patient fact sheets