Phthiriasis, Version 4,15.09.10

Condition / Phthiriasis (also Pediculosis ciliaris)
Aetiology / Infestation of lid margins by the crab louse (Phthirus pubis), a blood-feeding obligate ectoparasite affecting only humans
  • (NB in Pediculosis capitis, i.e. infestation by head lice (Pediculus humanis capitus), the lashes are rarely involved)
  • crab lice infest coarsely spaced hair, predominantly pubic hair
  • lashes also provide ideal spacing
  • genital-to-eye transmission, possibly on bedding and towels
  • crab lice survive no more than two days if separated from human host
  • this insect is not a vector for other diseases
  • in severe cases, lice faeces can cause keratoconjunctivitis
/ Love the bedding and towels – just been watching programme about Bill Clinton! Will cause amusement but short on evidence! Reminds me Of the lasides in GRU clinic getting VD from toilet seats.
Predisposing factors / Most common in young adults via sexual transmission
Can be contracted within families through poor hygiene
Symptoms / Intense itching of lid margins
Red watery eye
Unilateral or bilateral
Signs /
  • madarosis (loss of lashes)
  • conjunctival hyperaemia
  • superficial punctate keratopathy (SPK)
  • bites leave red inflamed areas on lid margins
  • possible pre-auricular lymphadenopathy
  • adult lice (1.0–1.5mm long) attached to lash; almost completely transparent (high magnification (x40) required at slit lamp)
  • eggs (termed nits) in greyish white cigar-shaped shells attached near base of lashes. Empty shells remain after hatching
  • reddish brown deposits at the base of the lashes are a mixture of louse faeces and host blood following louse bites

Differential diagnosis / Blepharitis (anterior)
Demodicosis (infestation by Demodex mites)
Allergic reactions affecting lid skin
Management by Optometrist
Non-pharmacological /
  • remove lice, nits and shells (casts) at slit lamp
  • use forceps (lice have a tenacious grip on the lashes)
  • sensitive counselling required as this is a sexually transmitted disease
  • NB possibility of sexual abuse of children
  • advise on any symptoms of pubic infestation
  • effective treatments (e.g. malathion, permathrin) available without prescription from pharmacies
  • these treatments are not suitable for use on the eyelid margins
  • sexual partners or family members at risk should have their eyes examined
  • bed linen, towels and clothes should be washed at 60°C for at least 5 min

Pharmacological /
  • Application of Simple Eye ointment to the lid margins will suffocate lice (unmedicated ointment, applied twice daily for at least 2 weeks)
  • Pilocarpine gel (see evidence base)
  • NB: insecticides can be toxic to the cornea

Referral
(Category) / Referral via GP for management of non-ocular aspects, including tracing and screening close contacts; also screening for other sexually-transmitted diseases
B2: Alleviation / palliation: normally no referral to ophthalmologist, unless heavy infestation present or does not respond to treatment
Possible management by Ophthalmologist
Heavy infestation can be reduced by Argon laser photo ablation or cryotherapy (freezing)
Evidence base
Clinical Effectiveness Group (British Association of Sexual Health and HIV)
United Kingdom National Guideline on the Management of Phthirus pubis infestation (2007)
Case report citing use of cholinergic agent:
Kumar N, Dong B, Jenkins C.Pubic lice effectively treated with Pilogel. Eye (2003);17:538–539
(Centre for Evidence-based Medicine Level of Evidence = 4)