Pediculosis and Pthiriasis

Eyelid infestation by Pediculus humanus.

Phthirus pubis, also known as pubic or crab louse, attached to a lid.

Pediculus is an organism 2-4 mm long that typically infests the hair of the patient. Infestation of the cilia is rare and only occurs in the worst cases. Pthirus is 2mm long with a broad-shaped, crab-like body. Its thick, clawed legs make it less mobile than the pediculus species and lend it to infesting areas where the adjacent hairs are within its grasp (eyelashes, beard, chest, axillary region, pubic region). Rarely does Pthirus infest the scalp. Both organisms suck the blood of the host, and Pediculus humanus may serve as a vector of diseases such as typhus and trench fever.

Ocular signs and symptoms include visible organisms within the scalp, hair, eyelashes or beard; visible blue skin lesions (louse bites), reddish brown deposits (louse feces), secondary blepharitis with preauricular adenopathy, follicular conjunctivitis and, in severe cases, marginal keratitis. The patient often presents with bilateral ocular itching and irritation. Superinfection of bites can lead to preauricular gland swelling.

Pathophysiology: Pediculus and Pthirus look alike and interbreed freely. Both types of lice lay eggs on the hair shafts, remaining firmly adherent, resisting both mechanical and chemical removal. Pediculus possesses good mobility and can pass from person to person by either close contact with an infested individual or by contact with contaminated bedding. Conversely, Pthirus are slow-moving organisms that cannot typically pass unless cilia is brought into close proximity with infested cilia. Both species are associated with crowding or poor personal hygiene.

Management: Management begins with forceps removal of all visible organisms and nits (eggs). Place the removed debris into an alcohol wipe and discard. Instruct the patient to obtain and use a pediculocidic medicated shampoo. These include, but are not limited to lindane 1%; permethrin 1% (marketed as Nix cream rinse by Warner-Lambert; Alimite cream by Allergan; or Acticin cream by Bertek); A-200 Pyrinate (pyrethrins, piperonyl butoxide and kerosene ); and Kwell or Rid, which are safe, effective, nonprescription pediculosides.

If it's not possible to physically remove the organisms, then topical ocular therapy is indicated. This may include smothering the lice and nits with petroleum jelly or other bland ointments tid; 1% yellow mercuric oxide, 20% fluorescein or 3% ammoniated mercuric oxide bid; or cholinesterase inhibitors such as physostigmine. Typically, the nits will survive a single application of these agents.

Clinical pearls:

• Daily follow up is required for 7-10 days, as nits hatch within that period.
• Instruct patients to thoroughly wash all clothing and linens that may have been exposed. Have them disinfect clothing, linen and personal items with heat of 50 degrees C (125 degrees F) for 30 minutes.
• Educate patients about how the organisms are transmitted, and advise that they should refrain from contact with others until the disease is 100% resolved. Finally, counsel patients to educate exposed partners to report for examination and evaluation.
• Due to ocular toxicity, pediculocide shampoos cannot be used to remove organisms from the eyelid.

Other reports in this section

• Molluscum Contagiosum
• Canaliculitis
• Verruca and Papilloma
• Pediculosis and Pthiriasis